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DC-DC charger (B2B) options and general discussion

..and do you have to have a VSR as a middleman between the alternator (indirect the starter battery) and the DC-DC to protect the starter battery from draining? Or am I getting something wrong?

So, alternator - starter battery - VSR - DCDC - LFP ?

Sorry for being noob, still trying to figure this out..

Some DC-DC chargers have an alternator sense that lets it know that the alternator is operating and it's OK to draw from the input source.
 
Some DC-DC chargers have an alternator sense that lets it know that the alternator is operating and it's OK to draw from the input source.
I already bought an VSR before I even knew I had to protect my alternator from my LFP, so I might as well use it... If the DC-DC charger that hasn't got the sense also is cheaper I might go for that! Any tips on model/brand for 12v system? I have an old car, so a DC-DC that doesnt pull too many amps if preferable
 
New thought! Could I just buy an Victron converter instead, like this one, "Victron Orion-Tr DC-DC converter" and then put the VSR between the alternator and the converter and then get the same function as a DC-DC charger? No?
 
'It is really important to understand that a VSR is “NOT” a battery charger. It is simply a switch that allows you to connect two batteries in parallel based on a pre-set voltage range. '

 
Just a very simple one. Using only this will cause problem by letting the LFP battery drain amps to fast and overheat the alternator, by the things I have read and understood. So. Putting a converter into the game as I write above.. What do you think?
 
Based on what I've heard of certain Victron DC-DC chargers, they have a built-in VSR. The Victron may be programmable which would allow you to cut off/begin charging at a higher threshold than 13.3v if you wanted to.
 
Just a very simple one. Using only this will cause problem by letting the LFP battery drain amps to fast and overheat the alternator, by the things I have read and understood. So. Putting a converter into the game as I write above.. What do you think?
The problem with that VSR is you shouldn't mix LFP and FLA batteries using it. It's fine if all batteries are the same type.
 
Is it OK to ask about an application that may become very common soon? Hybrid electric vehicles use 12 V for most purposes (other than traction and aircon), and they generally come with a 12 V ‘auxiliary’ battery (lead-acid, about 45 Ah) charged from the vehicle DC-DC converter. For some owners, it would make more sense to use LFP chemistry for the auxiliary battery (which does not crank an engine). The vehicle that I have tested (a 2019 rav4 hybrid) does seem to sense and send appropriate voltage to a 50 Ah LFP battery (14.2 V bulk stage, dropping to 13.6 V once the battery is charged). But at low SOC, an unregulated LFP battery can draw too much current for either the battery (1C) or the vehicle circuitry (~100 A). There is a single cable to deliver charge to and from the battery. Interposing a DC-DC charger would limit current to the battery, but these are generally unidirectional, so the battery can no longer provide power as needed. Bidirectional DC-DC converters exist, but currently they seem to be very expensive. Is it as simple as adding something like a Schottky power diode back from the battery to the vehicle circuit? Is there a better solution?
RavFuses.jpg
 
I just converted my RV to a Renogy 40A DCDC charger from a isolation solenoid. My only concern with the renogy is that it starts as soon as ignition is in on/run. I still have the intellitec voltage sensitive delay relay from the isolation solenoid setup, has anyone used this to control the 12v ignition signal to a renovy, seems likes a decent way to delay the start of charging to allow altenator to come up first (waits for 12 seconds of voltage being greater than 13.3v or something like that)
 
I just converted my RV to a Renogy 40A DCDC charger from a isolation solenoid. My only concern with the renogy is that it starts as soon as ignition is in on/run. I still have the intellitec voltage sensitive delay relay from the isolation solenoid setup, has anyone used this to control the 12v ignition signal to a renovy, seems likes a decent way to delay the start of charging to allow altenator to come up first (waits for 12 seconds of voltage being greater than 13.3v or something like that)
I did it and it works great, any one interested in a voltage sensitive relay with a time delay look at the intellitec 00-00629-120 isolator delay relay/e. They also make a 24v version, I think new they are like $43 on Amazon. Basically give some of the advantage of sterling or victron to the renogys only con is you still have to run the wire from ignition.
 
I did it and it works great, any one interested in a voltage sensitive relay with a time delay look at the intellitec 00-00629-120 isolator delay relay/e. They also make a 24v version, I think new they are like $43 on Amazon. Basically give some of the advantage of sterling or victron to the renogys only con is you still have to run the wire from ignition.
I'm looking at just adding a push button on the dash to manually activate the charger once I'm driving - run that also through an accessories line so that it only runs when the car does. Of course I still need to remember to turn it off, but it's cheaper and gives me more control.
 
I'm looking at just adding a push button on the dash to manually activate the charger once I'm driving - run that also through an accessories line so that it only runs when the car does. Of course I still need to remember to turn it off, but it's cheaper and gives me more control.
That's becoming nearly analogous with my "on-demand" Trailer Mod, Although a single-unit van has no need to boost the charge Voltage as far as I do. (I boost all the way to 36V, to reduce current through the 7-pin Bargman cable to the Trailer. In the Travel Trailer, I receive power into an MPPT controller which also runs regular panels "while camping", or whenever the Tow Vehicle high Voltage conversion has not been enabled.) In Vans, you guys can simply use a heavier wire all the way from the battery - but I LIKE and I DID do exactly as you have just described to enable all of the power consumption only on demand, with the habit of only switching it on while cruising.

Here is my dashboard, the switch becomes disabled when the (1) the ignition is not turned on; AND the secondary "Voltage Switcher Power Relay" only becomes active when the switch is enabled and flipped up. Completely on-the-fly, I can also turn it off while waiting at traffic lights and crawling through slow traffic in towns along the way.https://diysolarforum.com/threads/r...charge-solar-in-the-trailer.20730/post-242550
 
Reading another thread about a response from Kisae regarding their chargers, I came across this:
For the DMT1250: Up to 500W (600W allowable) for 12V and up to 750W (800W allowable) for 24V nominal panel arrays.
As I understand it, the DMT1250 has a 30A solar input. That means it will still output 50A at 12V (600W), provided the current from the solar panels is less equal to or than 30A and voltage is greater than or equal to 20V (600W), right?

Compared to the Renogy DCC50S which has a measly PV input of 25V, the 50V max on the Kisae means I can use these nominally 40V panels in parallel, right? For let's say, 390W+390W = 780W at 40V and 20A. Because I am overrating here, and providing more PV input than the charger can output, I should effectively be getting 600W for longer in the day with this setup than the 600W I'd receive from the DCC50S since that system would be at 17V nominally and it can only be overrated to 660W as I understand from their manual.

My question is; how much more efficient is the Kisae at 40V nominally than the Renogy DCC50S at 17V if they are both outputting 600W but being fed 780W and 660W respectively? What are some rough numbers for watts-per-day that I could glean from either of these systems, considering the 40V should charge off-peak longer than the 17V panels?
 
Reading another thread about a response from Kisae regarding their chargers, I came across this:

As I understand it, the DMT1250 has a 30A solar input. That means it will still output 50A at 12V (600W), provided the current from the solar panels is less equal to or than 30A and voltage is greater than or equal to 20V (600W), right?

Compared to the Renogy DCC50S which has a measly PV input of 25V, the 50V max on the Kisae means I can use these nominally 40V panels in parallel, right? For let's say, 390W+390W = 780W at 40V and 20A. Because I am overrating here, and providing more PV input than the charger can output, I should effectively be getting 600W for longer in the day with this setup than the 600W I'd receive from the DCC50S since that system would be at 17V nominally and it can only be overrated to 660W as I understand from their manual.

My question is; how much more efficient is the Kisae at 40V nominally than the Renogy DCC50S at 17V if they are both outputting 600W but being fed 780W and 660W respectively? What are some rough numbers for watts-per-day that I could glean from either of these systems, considering the 40V should charge off-peak longer than the 17V panels?
The higher voltage is always more efficient simply due to less VD on the PV circuit. So essentially it should produce more watts.

I have looked but never found a Kisae in a step up 12v DC to 24v DC. I'd be interested if they did and would like the ability to add portable panels to the PV input.
 
The higher voltage is always more efficient simply due to less VD on the PV circuit. So essentially it should produce more watts.

I have looked but never found a Kisae in a step up 12v DC to 24v DC. I'd be interested if they did and would like the ability to add portable panels to the PV input.
Gotcha' makes sense. Thanks. So I'm correct in understanding that the Kisae will output 50A at 12V so long as it gets fed 600W by whatever combination of voltage and current (below the 30A maximum) results in an incoming 600W to the controller? The 30A maxmium for the PV input in the manual is what had confused me.
 
Gotcha' makes sense. Thanks. So I'm correct in understanding that the Kisae will output 50A at 12V so long as it gets fed 600W by whatever combination of voltage and current (below the 30A maximum) results in an incoming 600W to the controller? The 30A maxmium for the PV input in the manual is what had confused me.
Start on this page, a member had asked Kisae for more information. Note the limits on amps, so they only choice is higher V.
 
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