Renogy DCC50S or Kisae DMT1250?

[steven1955]

I've seen too many FDLFBR (Friends don't let friends by Renogy) comments.

The application is the updating of our 1975 FMC 2900R motorhome to lithium with (hopefully) near term future solar. 270-ish Ah of cooked AGM batteries are being replaced with 400 Ah of LiFePO4 batteries.

On paper the Renogy DCC50S wins due to automatic voltage sensing, an ability to top off the starter battery when the house batteries are fully charged, and Bluetooth communication via their BT-2 Bluetooth module.

The Kisae DMT1250 has a higher solar input voltage and, for those FDLFBR commenters, it's not a Renogy.

What would you buy?

Stirling also has a DC to DC charger with MPPT solar capability, but it's pretty pricey and limited to 30 amps. Victron is also limited to 30 amps and would require two boxes as they don't currently offer a combined DC to DC/MPPT solar charger.

 

[fratermus]

Full disclosure: I have no dog in the fight. I own no Renogy products and do my charging with standalone solar charge controller and VSR.

I've seen too many FDLFBR (Friends don't let friends by Renogy) comments.

FDLFBR is an indicator of fixated thinking, counterproductive IMO on a forum dedicated to DIY projects and experimentation. It is often repeated by people who cannot correctly copy the word Renogy when it is right in front of them, veering off into Renolgy, Renology, Renergy, or some other string of letters. It's a shibboleth that outs the inattentive.

/rant mode off

On paper the Renogy DCC50S wins due to automatic voltage sensing,

The Kisae manual suggests alternator charging starts when chassis voltage ≥13.2v. This can start lower if overridden or if D+ is provided on the controller terminal. Am I misreading this? Can anyone with the unit please confirm one way or another?

The other two points are fair.

The Kisae DMT1250 has a higher solar input voltage

The Kisae's higher PV input limit is a serious benefit to folks who want to run panels higher than nominal 12v, or "12v" panels that are on the high end of that range. My understanding is it also will deliver the full rated power from alternator by default, even with solar available.

Of the two I have only had hands on the Renogy DCC50. It worked as advertised. I think I would use whichever I preferred, or whichever I could source with least expense. Do let us know what you pick and report back how it works. FDLFBRers be damned.

 

[tim0shel]

I am still concidering one of these two myself for backup charging my portable setup. Would be great to even mount it in my Aux battery build to my main solar generator. At the same time I think having one of these just mounted in the car with the car's solar running through would be better way to go. Then have my portable panel setup running through the SCC in the solar generator. Either way it would be great piece of equipment to have. Look forward to hearing others that have used either of these devices.

 

[steven1955]

Can you update the software in Renogy devices yourself? You cannot update software in the Kisae devices except by sending back to Kisae North America. (This is per Ricardo of Kisae NA, and he says they normally send you a refurbished unit with the newest software for a fee. You really gotta need that new software to go through this.)

So, yes, I spoke to with Ricardo of Kisea NA and got a few details of their DMT1250.

1. Unlike the Renogy DCC50S the DMT1250 can only charge batteries from either the alternator or solar, never both at the same time, and if there is alternator power it will charge from the alternator preferentially over solar.

1a. The above might be an advantage for the Kisae because the Renogy with today's software will reduce alternator charging from 50 to 25 amps if any solar is available. If only, say, 10 amps of solar is available you would be charging at 35 amps, 25 amps alternator plus 10 amps solar.

1b. This is why I asked about field reprogramming of Renogy devices. I could see where the Renogy software, if updated, could vary the alternator contribution to complement the solar to always give you 50 amps total.

1c. This would not be possible on the Kisae DMT1250 as it only has one DC to DC converter that is switched between alternator and solar inputs. But you'll always have 50 amps if you have a running alternator.

1d. There is no way to force solar preferentially over alternator charging on either except to disconnect the heavy gauge alternator input.

2. The Kisae DMT1250 is voltage sensing like the Renogy DCC50S to start charging from the alternator. It also has, like the Renogy, a connection to force start alternator charging if the input voltage is too low, like a smart alternator.

3. No Bluetooth monitoring of the Kisae, only the built in screen or a wired remote version of the built in screen. The Renogy can have either Bluetooth monitoring or a remote wired display.

4. No starter battery trickle charging function on the Kisae.

Still deciding.... Still deciding.....

 

[tim0shel]

Can you update the software in Renogy devices yourself? You cannot update software in the Kisae devices except by sending back to Kisae North America. (This is per Ricardo of Kisae NA, and he says they normally send you a refurbished unit with the newest software for a fee. You really gotta need that new software to go through this.)

So, yes, I spoke to with Ricardo of Kisea NA and got a few details of their DMT1250.

1. Unlike the Renogy DCC50S the DMT1250 can only charge batteries from either the alternator or solar, never both at the same time, and if there is alternator power it will charge from the alternator preferentially over solar.

1a. The above might be an advantage for the Kisae because the Renogy with today's software will reduce alternator charging from 50 to 25 amps if any solar is available. If only, say, 10 amps of solar is available you would be charging at 35 amps, 25 amps alternator plus 10 amps solar.

1b. This is why I asked about field reprogramming of Renogy devices. I could see where the Renogy software, if updated, could vary the alternator contribution to complement the solar to always give you 50 amps total.

1c. This would not be possible on the Kisae DMT1250 as it only has one DC to DC converter that is switched between alternator and solar inputs. But you'll always have 50 amps if you have a running alternator.

1d. There is no way to force solar preferentially over alternator charging on either except to disconnect the heavy gauge alternator input.

2. The Kisae DMT1250 is voltage sensing like the Renogy DCC50S to start charging from the alternator. It also has, like the Renogy, a connection to force start alternator charging if the input voltage is too low, like a smart alternator.

3. No Bluetooth monitoring of the Kisae, only the built in screen or a wired remote version of the built in screen. The Renogy can have either Bluetooth monitoring or a remote wired display.

4. No starter battery trickle charging function on the Kisae.

Still deciding.... Still deciding.....

Yet you make it still dificult to decide lol

 

[fratermus]

Can you update the software in Renogy devices yourself?

I don't know of any DC-DC/MPPT combo units that are field upgradable. If anyone knows otherwise please chime in.

 

[steven1955]

I am choosing the Renogy DCC50S over the Kisae DMT1250. The reasons are:

1. The Renogy will charge the starter battery when the house batteries are fully charged.
2. The Renogy has bluetooth communication vs the wired remote of the Kisae.
3. Amazon has a sale offering the DCC50S for $208.16 today. That's instead of the more normal $265, and who knows how long this sale will last.

I am concerned that I may get burned with this purchase, but I am thinking that the failures are few. In addition to the vocal folks with failed units, there seem to be a lot of folks happy with their install.

 

[bedpan]

I am choosing the Renogy DCC50S over the Kisae DMT1250. The reasons are:

1. The Renogy will charge the starter battery when the house batteries are fully charged.
2. The Renogy has bluetooth communication vs the wired remote of the Kisae.
3. Amazon has a sale offering the DCC50S for $208.16 today. That's instead of the more normal $265, and who knows how long this sale will last.

I am concerned that I may get burned with this purchase, but I am thinking that the failures are few. In addition to the vocal folks with failed units, there seem to be a lot of folks happy with their install.

For what its worth.. Ordering direct from Renogy you can usually get 10% off with a coupon code. Will has (had?) one, if not ask away here I am sure someone will share.

Further In Canada anyways its free shipping and no tax. In Canada Renogy is almost always cheaper.

 

[Sparks99]

I am choosing the Renogy DCC50S over the Kisae DMT1250. The reasons are:

1. The Renogy will charge the starter battery when the house batteries are fully charged.
2. The Renogy has bluetooth communication vs the wired remote of the Kisae.
3. Amazon has a sale offering the DCC50S for $208.16 today. That's instead of the more normal $265, and who knows how long this sale will last.

I am concerned that I may get burned with this purchase, but I am thinking that the failures are few. In addition to the vocal folks with failed units, there seem to be a lot of folks happy with their install.

I have the Kisae Abso DMT1250 and it's pretty good all around, it would be nice if there was a remote on/off pin for the alternator input rather than the current functionality which just drops the threshold voltages but you can always add an external breaker as others have suggested. Generally the Abso unit has performed well, I have only a couple of issues with it, if you turn it off via the rocker switch it forgets its user-set battery max charging current value and defaults to max (50A) on powering up again, this is a problem for small batteries (<= 100AH) or for small/heavily loaded alternators.
The other issue is more relevent to dark/wet climates like ours, the unit draws its power from the leisure battery and under very low solar inputs it drains more from the battery than it produces from the panel. The panel input low-voltage-cutoff should be higher. It's an issue if you are trying to claw every solar watt out of constantly overcast/wet skies.
Other than that it performs very well, I have a 34v nominal panel (40v max) and the DMT1250 handles it with ease.

The DCDC charger works well, when it's active the unit disables the solar input but that makes for a better charge since the solar panel illumination can vary constantly whilst driving leading to erratic charging currents, with alternator charging the bulk and absorbtion current is at the max setting all the time, even at idle. You have to be a bit careful not to cook your alternator though (as with any DCDC charging) especially with big batteries.

I still can't find an alternative to the DMT1250 unit which takes the same high panel voltage and provides good DCDC charging, I'm surprised Victron haven't figured it out, they have both MPPT solar and DCDC chargers but not a combined unit and whenever you combine victron gear you always waste a lot of (expensive) functionality in duplication.

The Abso unit has been very reliable so far, I've run it for a couple of years, the internal build quality is quite satisfactory as far as I'm concerned. The remote display isn't really needed, nor is bluetooth, after glancing in the display panel a few times it's a fit-forget device and the battery monitor sounds the alarm anyway, if needed. It's still the most convenient and best value solar/DCDC charger I can find.

It also works in power-supply mode, some chargers refuse to do that but this one keeps the solar input active even when the battery is floating and if there's sufficient sun then the unit supplies all the load current up to it's max. output current. This is handy as it reduces the cyclic load on the battery.

The passive cooling is usually enough since the main part of the unit is extruded aluminium but if it charges at max current in a hot environment (it only gets warm at ambient 25 degrees C) then the internal fan starts up and it's not a screamer so it's not a problem.

 

[RV8R]

I have the Kisae Abso DMT1250 and it's pretty good all around, it would be nice if there was a remote on/off pin for the alternator input rather than the current functionality which just drops the threshold voltages but you can always add an external breaker as others have suggested. Generally the Abso unit has performed well, I have only a couple of issues with it, if you turn it off via the rocker switch it forgets its user-set battery max charging current value and defaults to max (50A) on powering up again, this is a problem for small batteries (<= 100AH) or for small/heavily loaded alternators.
The other issue is more relevent to dark/wet climates like ours, the unit draws its power from the leisure battery and under very low solar inputs it drains more from the battery than it produces from the panel. The panel input low-voltage-cutoff should be higher. It's an issue if you are trying to claw every solar watt out of constantly overcast/wet skies.
Other than that it performs very well, I have a 34v nominal panel (40v max) and the DMT1250 handles it with ease.

The DCDC charger works well, when it's active the unit disables the solar input but that makes for a better charge since the solar panel illumination can vary constantly whilst driving leading to erratic charging currents, with alternator charging the bulk and absorbtion current is at the max setting all the time, even at idle. You have to be a bit careful not to cook your alternator though (as with any DCDC charging) especially with big batteries.

I still can't find an alternative to the DMT1250 unit which takes the same high panel voltage and provides good DCDC charging, I'm surprised Victron haven't figured it out, they have both MPPT solar and DCDC chargers but not a combined unit and whenever you combine victron gear you always waste a lot of (expensive) functionality in duplication.

The Abso unit has been very reliable so far, I've run it for a couple of years, the internal build quality is quite satisfactory as far as I'm concerned. The remote display isn't really needed, nor is bluetooth, after glancing in the display panel a few times it's a fit-forget device and the battery monitor sounds the alarm anyway, if needed. It's still the most convenient and best value solar/DCDC charger I can find.

It also works in power-supply mode, some chargers refuse to do that but this one keeps the solar input active even when the battery is floating and if there's sufficient sun then the unit supplies all the load current up to it's max. output current. This is handy as it reduces the cyclic load on the battery.

The passive cooling is usually enough since the main part of the unit is extruded aluminium but if it charges at max current in a hot environment (it only gets warm at ambient 25 degrees C) then the internal fan starts up and it's not a screamer so it's not a problem.

There is a way for a remote signal “switch” on/off

 

[fratermus]

it would be nice if there was a remote on/off pin for the alternator input

See this thread on another forum; per Kisae you can shut down charging by inducing a fake E07 condition. This could be useful for manual intervention, low-temp protection, etc.

 

[RV8R]

I have the Kisae Abso DMT1250 and it's pretty good all around, it would be nice if there was a remote on/off pin for the alternator input rather than the current functionality which just drops the threshold voltages but you can always add an external breaker as others have suggested. Generally the Abso unit has performed well, I have only a couple of issues with it, if you turn it off via the rocker switch it forgets its user-set battery max charging current value and defaults to max (50A) on powering up again, this is a problem for small batteries (<= 100AH) or for small/heavily loaded alternators.
The other issue is more relevent to dark/wet climates like ours, the unit draws its power from the leisure battery and under very low solar inputs it drains more from the battery than it produces from the panel. The panel input low-voltage-cutoff should be higher. It's an issue if you are trying to claw every solar watt out of constantly overcast/wet skies.
Other than that it performs very well, I have a 34v nominal panel (40v max) and the DMT1250 handles it with ease.

The DCDC charger works well, when it's active the unit disables the solar input but that makes for a better charge since the solar panel illumination can vary constantly whilst driving leading to erratic charging currents, with alternator charging the bulk and absorbtion current is at the max setting all the time, even at idle. You have to be a bit careful not to cook your alternator though (as with any DCDC charging) especially with big batteries.

I still can't find an alternative to the DMT1250 unit which takes the same high panel voltage and provides good DCDC charging, I'm surprised Victron haven't figured it out, they have both MPPT solar and DCDC chargers but not a combined unit and whenever you combine victron gear you always waste a lot of (expensive) functionality in duplication.

The Abso unit has been very reliable so far, I've run it for a couple of years, the internal build quality is quite satisfactory as far as I'm concerned. The remote display isn't really needed, nor is bluetooth, after glancing in the display panel a few times it's a fit-forget device and the battery monitor sounds the alarm anyway, if needed. It's still the most convenient and best value solar/DCDC charger I can find.

It also works in power-supply mode, some chargers refuse to do that but this one keeps the solar input active even when the battery is floating and if there's sufficient sun then the unit supplies all the load current up to it's max. output current. This is handy as it reduces the cyclic load on the battery.

The passive cooling is usually enough since the main part of the unit is extruded aluminium but if it charges at max current in a hot environment (it only gets warm at ambient 25 degrees C) then the internal fan starts up and it's not a screamer so it's not a problem.

Great Write Up @Sparks99 ?

I recently installed the Kisae 1250 in my van & custom programmed it for the 50 amp max, so would not know if I had a lower max current if the custom resorts back to the 50 amp max default if I use the toggle ( I don’t use the toggle anyway ).

I also do not use the solar charger side of the Kisae as I do not have solar on my van ,,, maybe someday a probable Boondocking panel will be kept under the bed.

The thermal forced error shutoff will turn the entire unit off I believe. So if that works for your purpose great ?. Another method would to place a solenoid between the starter positive & the Kisae. Then this solenoid could be “cockpit” controlled by the driver & would not effect the solar side.

I have 4 way Blue Sea switches on both positive wires between Kisae & House Battery then another one Starter Battery & Kisae. I posted about this method I designed for my van ( Promaster ) here;

The Big Red (4 Way) Switch 😁

www.fordtransitusaforum.com

My Kisae 1250 Install starts on this post;

RV8Rs New Build - TETRIS

www.promasterforum.com

 

[Sparks99]

Nice idea but no, I wouldn't want to shut down the entire unit, I'd want the solar to be active all the time and if my alternator was maxed out or running hot or I wanted to let the cold engine warm up before adding the extra loading I'd want to disable the alternator input only. Although I could lash one up I'm considering just buying the Victron 65A battery isolator for that purpose, the standby current is low and the dropout voltage should be minimal. It's unidirectional but if I need to charge the van battery from the solar in an emergency I'll lash up a temporary connection anyway.
Ideally there would be an analogue input to the DMT1250 which would derate the alternator input current draw in proportion to the applied voltage which would allow implementation of alternator load sensing/derating. Also tying it to 0v would disable the alternator input entirely giving you the "remote switch" functionality.

I also have a cheap mains-charging option for the DMT1250 which works well, rather than the Victron solution of "have 2 chargers already? Just buy another one!" I use the one charger (the DMT1250) and via a mains-powered double-pole changeover relay feed 43V DC into the solar input from a cheap chinese 48V SMPSU, I think it was £26 on fleabay. That way when shore power is connected the DMT1250 automatically switches from solar to mains power and its MPPT algorithm works fine with a low impedance source and draws maximum current from the power supply without any messing around.
The SMPSU has an output adjustment trimmer which lets you take it well below the DMT1250 maximum solar input voltage so it's safe to use, ok you lose a little bit of power since the SMPSU is current limited rather than power limited but the battery max. charge current limit is the limiting factor anyway.
It beats having 2 chargers connected to the same battery both fighting each other for abs/float and it's cheaper too. The SMPSU fan is small and therefore noisy but you can easily replace it with an external larger, quieter PC fan and the fan only comes on when the SMPSU is sourcing over a certain current anyway. The SMPSU only gets warm at max output anyway so the fan is hardly needed, surprising for a cheap chinese thing, it hasn't blown up to date either, bonus!
I figure that the solar input capacitance will be fairly low so sudden switching from the 43V PSU to (say) dark solar cells shouldn't cause it stress, if you imagine driving under a low bridge on a Summer's day the solar input sees 0-100% step changes anyway. It's been fine in practice.

 

[Sparks99]

Great Write Up @Sparks99 ?

I recently installed the Kisae 1250 in my van & custom programmed it for the 50 amp max, so would not know if I had a lower max current if the custom resorts back to the 50 amp max default if I use the toggle ( I don’t use the toggle anyway ).

I also do not use the solar charger side of the Kisae as I do not have solar on my van ,,, maybe someday a probable Boondocking panel will be kept under the bed.

The thermal forced error shutoff will turn the entire unit off I believe. So if that works for your purpose great ?. Another method would to place a solenoid between the starter positive & the Kisae. Then this solenoid could be “cockpit” controlled by the driver & would not effect the solar side.

I have 4 way Blue Sea switches on both positive wires between Kisae & House Battery then another one Starter Battery & Kisae. I posted about this method I designed for my van ( Promaster ) here;

The Big Red (4 Way) Switch 😁

www.fordtransitusaforum.com

View attachment 183735






My Kisae 1250 Install starts on this post;

RV8Rs New Build - TETRIS

www.promasterforum.com

Ok, my only concern is in switching over the house battery to/from the power centre, the "dead time" will have to absolutely minimal because the DMT1250 draws its operating current from the house battery and the moment you disconnect it the unit powers down, it won't draw its internal electronics current from the vehicle battery in that situation (for obvious reasons). If your changeover causes enough input voltage sag then you risk the DMT browning out if the inputs are inactive or possibly over-volting if either input is active, either case is very undesirable. If you were going to operate the switch it would probably be best to shut down the DMT at the rocker switch first, unless the switch travel is pretty much instant. You wouldn't want a make-before-break action either (to counter this issue) since that would briefly short the power centre and house battery together. A large input capacitor might be enough to coast the DMT safely through the transition.

*********************

I just checked that switch online, it definitely has an "off" position, the DMT1250 requires a permanent connection to the house battery, it's certainly not intended to run with it open circuit. That big rotary switch will have long gaps between changeovers anyway, I really think you should reconsider your setup or at the least make sure you power down the DMT1250 before switching house batteries. The manual says that the house battery should be connected first and disconnected last so if you open the "starter" isolator (and solar isolator if you fit it) and then the house battery changeover switch you should be ok.

Also I didn't know what the Parallax 8355 unit was, I assumed it was some sort of portable battery/powerstation, I looked it up and it's a mains charger/12v supply and distribution unit, ok. The battery charger in the 8355 says it's a 3 stage type, for the sake of your expensive AGMs let's hope so but you will certainly want to buy and fit the remote temperature monitor kit for it : Parallax 8300 series user manual

However the way you have shown it wired in the above diagram, if the terminal you marked "L" is the output terminal on the BlueSea switch (Blue Sea e-series) then in the 1 position the AGMs are connected to the 8355 and the DMT1250 is isolated, that's fine (IF the DMT1250 is shut down) but in 1+2 position the AGMs, 8355 AND DMT1250 are all connected together at once which isn't fine since you have 2 chargers fighting each other. Worst still in the 2 position the AGMs are disconnected and the 8355 and DMT1250 are connected together! Definitely not.

The AGMs should be on the Output ("L") pin, the 8355 should be on Input 2 and the DMT1250 should be on Input 1, that way when the Alternator rotary switch is also in position 1 the alternator is connected to the DMT1250. You should isolate the alternator input before switching the batteries over to the 8355 so the DMT1250 isn't running with nothing connected to the house battery output.

Since you never want to combine the 8355 and DMT1250 I suggest that the 3 position switch is a better choice than the 4 position one, that gives you the choice of DMT1250, Off (battery isolated) or 8355 shore charger. (Blue Sea m-series 3 posn)

 

[RV8R]

Ok, my only concern is in switching over the house battery to/from the power centre, the "dead time" will have to absolutely minimal because the DMT1250 draws its operating current from the house battery and the moment you disconnect it the unit powers down, it won't draw its internal electronics current from the vehicle battery in that situation (for obvious reasons). If your changeover causes enough input voltage sag then you risk the DMT browning out if the inputs are inactive or possibly over-volting if either input is active, either case is very undesirable. If you were going to operate the switch it would probably be best to shut down the DMT at the rocker switch first, unless the switch travel is pretty much instant. You wouldn't want a make-before-break action either (to counter this issue) since that would briefly short the power centre and house battery together. A large input capacitor might be enough to coast the DMT safely through the transition.

*********************

I just checked that switch online, it definitely has an "off" position, the DMT1250 requires a permanent connection to the house battery, it's certainly not intended to run with it open circuit. That big rotary switch will have long gaps between changeovers anyway, I really think you should reconsider your setup or at the least make sure you power down the DMT1250 before switching house batteries. The manual says that the house battery should be connected first and disconnected last so if you open the "starter" isolator (and solar isolator if you fit it) and then the house battery changeover switch you should be ok.

Also I didn't know what the Parallax 8355 unit was, I assumed it was some sort of portable battery/powerstation, I looked it up and it's a mains charger/12v supply and distribution unit, ok. The battery charger in the 8355 says it's a 3 stage type, for the sake of your expensive AGMs let's hope so but you will certainly want to buy and fit the remote temperature monitor kit for it : Parallax 8300 series user manual

However the way you have shown it wired in the above diagram, if the terminal you marked "L" is the output terminal on the BlueSea switch (Blue Sea e-series) then in the 1 position the AGMs are connected to the 8355 and the DMT1250 is isolated, that's fine (IF the DMT1250 is shut down) but in 1+2 position the AGMs, 8355 AND DMT1250 are all connected together at once which isn't fine since you have 2 chargers fighting each other. Worst still in the 2 position the AGMs are disconnected and the 8355 and DMT1250 are connected together! Definitely not.

The AGMs should be on the Output ("L") pin, the 8355 should be on Input 2 and the DMT1250 should be on Input 1, that way when the Alternator rotary switch is also in position 1 the alternator is connected to the DMT1250. You should isolate the alternator input before switching the batteries over to the 8355 so the DMT1250 isn't running with nothing connected to the house battery output.

Since you never want to combine the 8355 and DMT1250 I suggest that the 3 position switch is a better choice than the 4 position one, that gives you the choice of DMT1250, Off (battery isolated) or 8355 shore charger. (Blue Sea m-series 3 posn)

I like the way you think @Sparks99 ? ,,, & thanks for the heads up !!

To begin, everything I did to hook up my Kisae 1250 I vetted & got sanctioned by Kisae’s tech “Ricardo”. I will research your concern a little more, as things can get missed.


The Blue Sea 4 way switch; procedure is always from off to #1 (house battery) to 1&2 both batteries ,,, #2 is never used & the shut down is the opposite process. I think off to one is the only open circuit & 1 to 1&2 does not break “open” the circuit. Caveat, I have not talked to Blue Sea about this assumption, but the way it acts I do not detect an open circuit condition.

I fully understand “chargers fighting” & that inboard converter & 120vac is rarely rarely used. If I build another van ( this is my second one ) I do not think I would install 120vac at all. The 120vac & van engine are never used together. That converter/charger is only when on Shore Power.

The Alternator switch is kept off unless the house battery is connected to the Kisae 1st.

 

[RV8R]

Ok, my only concern is in switching over the house battery to/from the power centre, the "dead time" will have to absolutely minimal because the DMT1250 draws its operating current from the house battery and the moment you disconnect it the unit powers down, it won't draw its internal electronics current from the vehicle battery in that situation (for obvious reasons). If your changeover causes enough input voltage sag then you risk the DMT browning out if the inputs are inactive or possibly over-volting if either input is active, either case is very undesirable. If you were going to operate the switch it would probably be best to shut down the DMT at the rocker switch first, unless the switch travel is pretty much instant. You wouldn't want a make-before-break action either (to counter this issue) since that would briefly short the power centre and house battery together. A large input capacitor might be enough to coast the DMT safely through the transition.

*********************

I just checked that switch online, it definitely has an "off" position, the DMT1250 requires a permanent connection to the house battery, it's certainly not intended to run with it open circuit. That big rotary switch will have long gaps between changeovers anyway, I really think you should reconsider your setup or at the least make sure you power down the DMT1250 before switching house batteries. The manual says that the house battery should be connected first and disconnected last so if you open the "starter" isolator (and solar isolator if you fit it) and then the house battery changeover switch you should be ok.

Also I didn't know what the Parallax 8355 unit was, I assumed it was some sort of portable battery/powerstation, I looked it up and it's a mains charger/12v supply and distribution unit, ok. The battery charger in the 8355 says it's a 3 stage type, for the sake of your expensive AGMs let's hope so but you will certainly want to buy and fit the remote temperature monitor kit for it : Parallax 8300 series user manual

However the way you have shown it wired in the above diagram, if the terminal you marked "L" is the output terminal on the BlueSea switch (Blue Sea e-series) then in the 1 position the AGMs are connected to the 8355 and the DMT1250 is isolated, that's fine (IF the DMT1250 is shut down) but in 1+2 position the AGMs, 8355 AND DMT1250 are all connected together at once which isn't fine since you have 2 chargers fighting each other. Worst still in the 2 position the AGMs are disconnected and the 8355 and DMT1250 are connected together! Definitely not.

The AGMs should be on the Output ("L") pin, the 8355 should be on Input 2 and the DMT1250 should be on Input 1, that way when the Alternator rotary switch is also in position 1 the alternator is connected to the DMT1250. You should isolate the alternator input before switching the batteries over to the 8355 so the DMT1250 isn't running with nothing connected to the house battery output.

Since you never want to combine the 8355 and DMT1250 I suggest that the 3 position switch is a better choice than the 4 position one, that gives you the choice of DMT1250, Off (battery isolated) or 8355 shore charger. (Blue Sea m-series 3 posn)

Hi @Sparks99

I recently receive back an email from Kisae & they have indicated my design should not create any damage to the Kisae 1250.

Here is a schematic;