I'm converting my house batteries in a motorhome to LifePO4 and considering staying with a 12v bank for now since that is the way the current inverter is setup. I would like to be able to gently maintain charge on the FLA chassis batteries when parked and be able to charge LifePO4 house batteries from alternator when driving at night (ignoring solar at this point). Is there a single device that will charge both ways, or do I need to just buy 2 DC to DC chargers? If two chargers, is there an easy way to turn each charger on and off? I'm guessing the alternator charging one could be switched from the ignition and the other just the inverse (i.e. on whoever ignition is off)?
DC to DC 2-Way Charger?
- Thread starter tonkamog
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Ranger Rick
Here comes the sun
Renogy DCC50S 12V 50A DC-DC (Deleted)
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downhiller
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Are you sure Ranger Rick, I don't see anything on Renogy's product page on their website that indicates it'll charge the chassis battery as well, neither from the solar or the house batteries?:
uk.renogy.com
DCC50S 12V 50A DC-DC On-Board Battery Charger with MPPT(New Version)
Renogy DCC50S DC to DC charger with solar input is used for charging a solar battery. The solar power battery charger charges the leisure battery w/ solar power.
uk.renogy.com
I appreciate the input so far. I'm likely going to call Renogy. I don't see anything on their website that indicates this will charge multiple independent battery banks. It will handle multiple charge input sources. I'll report back here if I get an answer from them.
Ranger Rick
Here comes the sun
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Ranger Rick
Here comes the sun
Google “will a vehicle battery drain an rv battery”
I do see that the Renogy unit has an isolator, so it won’t allow Rv to mv reverse charging. Cheapest way would be a small solar charger.
I do see that the Renogy unit has an isolator, so it won’t allow Rv to mv reverse charging. Cheapest way would be a small solar charger.
Ranger Rick
Here comes the sun
Correct as its specs state, “Renogy DC-DC On-Board Battery Charger has multiple intelligent protections includes (sic) battery isolation … .”
downhiller
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It seems surprising to me that there isn't a "one box does all". Connect your solar to it, your house battery, your starter battery and all of your dc loads to it. A nice remote panel and bluetooth connectivity to configure it however you want.
If I'm right in that no-one makes that yet, I can only assume we'll see such a product in a year or two.
If I'm right in that no-one makes that yet, I can only assume we'll see such a product in a year or two.
downhiller
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FWIW though, Will Prowse claims:
"Trickle charges the starting battery via solar panels if the service battery is fully charged"
In the first post of this monster thread:
diysolarforum.com
(I've not read any further yet)
"Trickle charges the starting battery via solar panels if the service battery is fully charged"
In the first post of this monster thread:
Renogy DC DC Charger w/ MPPT
Finally reviewed it! People asked me repeatedly, and I was too busy with the solar shed. For the last few days, I tested it like crazy.. And I love it! I should have tested it months ago. Works extremely well, and it's fool proof. I pushed it to every limit, and if it cut off, it would restart...
diysolarforum.com
(I've not read any further yet)
stienman
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You indicated one power source - the alternator - and two power sinks - a chassis battery, and a LiFePO4 battery.
Presumably the alternator and chassis battery are already wired to charge the chassis battery when the motor is running.
Charging the LiFePO4 batteries with an automatic battery switch would solve the second part of your question. Look for "Dual battery isolator" for a lot of products. These allow a great deal of charging current to flow, much more than a trickle charge.
It sounds like, if I'm not mistaken, you want to then charge the chassis battery from the LiFePO4 battery when the alternator isn't running?
When the vehicle is off, the loads on the chassis battery shouldn't exceed 1A, so the simple solution is to have a 1A 13.5v current and voltage limited regulator coming from the LiFePO4 battery. There are a lot of solutions for this, most under $20. Look for "Buck boost 12v converter". Make sure you can set both the voltage and the current limits, that way if you do leave on your headlights you'll only drain the LiFEPO4 batteries at a rate of 1A. Look for one that has "anti backflow" protection, such as this one:
This prevents the regulator from going crazy when the alternator is on and the output of the regulator is being driven to a higher voltage by the alternator. If your DC-DC converter doesn't have this, a diode can be used, and you'd set the voltage higher to account for the diode drop.
Honestly, though, I'm having a hard time understanding the reason for the second part of your requirement. You shouldn't have to float charge it unless it's going to sit unused for more than a week or two unused. If you find that you do, then you have loads on it that should probably be on your other battery. Needing a float charger usually indicates there's some other problem that should be resolved first - unless it's simply that you plan on not running the vehicle for several weeks at a time - and in that case you really should run the engine for 30 minutes every week or more anyway to keep things lubricated, which would also manage the battery drain.
At any rate, no, there's no all in one device, and I wouldn't hold my breath for one. Your use case is unusual. Further, there's no advantage to trying to create something that does both - the first requirement has a huge current passing requirement, but no voltage conversion, so it's literally a switch controlled by the voltage - if it's above 13.5v then the alternator is running, and the switch is on. If it's below that then the switch is off because the alternator isn't on, or isn't supplying enough power to charge the second battery.
The second requirement does require a voltage converter, since you only want trickle charging, and the LiFePO4 battery is likely below the 14+v needed to account for a diode or regulator vdrop even when it has most of its energy left. Otherwise you could just use another switch to allow the batteries to charge/discharge to the same voltage level.
Right, but I cannot find that statement on the Renogy site or in the manual. And, maybe my mind or eyes are playing tricks on me, but that statement is not on Will’s blueprint page for this.FWIW though, Will Prowse claims:
"Trickle charges the starting battery via solar panels if the service battery is fully charged"
In the first post of this monster thread:
Renogy DC DC Charger w/ MPPT
Finally reviewed it! People asked me repeatedly, and I was too busy with the solar shed. For the last few days, I tested it like crazy.. And I love it! I should have tested it months ago. Works extremely well, and it's fool proof. I pushed it to every limit, and if it cut off, it would restart...
(I've not read any further yet)
There are a few of us, or maybe just me, with a legitimate use case for this, hence the plethora of high amp VSRs (and some with an override to provide a boost to the starter and configurable to prevent overcharging of Lithium batteries, ie the relay keeps things isolated until the starter battery is low enough and the house is high enough).
A manual switch would work too, but gotta be careful not to leave it in the “wrong” setting and destroy your starter or house battery.
Me? I’m out in remote areas in the cold, -10F to -20F, and I’ve had times where I’ve wished to have a boost to turn my starter over (even with two starter batteries). I make it out, but some extra security is welcome. And, sometimes starter batteries go bad in the cold (it seems or even tests fine until cold temps really stress it). Heck, even just lots of small trips in the dark and cold of the North can never let the alternator catch up. I’ve also heard of some Sprinters conversions with a “starter boost” button for similar purposes, so this must be useful to some.
stienman
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In my 2009 Econoline E350 van there is a relay built in that connects the secondary battery when the key is in the run position - I'm not sure whether it's also on in the start position. This means the secondary gets charged when the van is running. Since the start position is just past run, however, then leaving it in run for several minutes before starting the engine will effectively charge the primary battery from the secondary - as long as I've turned off the headlights, blowers, and anything else that consumes a lot of current.
It may be that what you should consider is a high amp relay that connects the two batteries in parallel in the run and start positions. The only downside is you might have to wait a few minutes when the equalize, compared to having a trickle charger/maintainer always on the primary.
It may be that what you should consider is a high amp relay that connects the two batteries in parallel in the run and start positions. The only downside is you might have to wait a few minutes when the equalize, compared to having a trickle charger/maintainer always on the primary.
downhiller
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I'm in the process of planning my setup, and have read "friends don't let friends buy renogy" too often, so I think I'm going for separate Victron DCDC charger and MPPT solar controller.
As I understand, this WILL NOT allow the starter battery to charge from the house battery bank, correct?
I'm thinking of putting a small solar panel and cheap PWM (or cheap MPPT) and having them connected solely to the starter battery. In addition to the "main" solar/MPPT setup on the house batteries.
It's not as clever as a two-way system, but the panel/SCC will be cheap, and it should do the job, and I'll never have to worry about a flat battery after leaving the van for a few weeks again. Worth it?
Any problems with this approach?
In an ideal world I'd go and start the van up and run it for a while every week or so if I'm not using it, but reality is I'm rubbish at doing that sort of thing.
As I understand, this WILL NOT allow the starter battery to charge from the house battery bank, correct?
I'm thinking of putting a small solar panel and cheap PWM (or cheap MPPT) and having them connected solely to the starter battery. In addition to the "main" solar/MPPT setup on the house batteries.
It's not as clever as a two-way system, but the panel/SCC will be cheap, and it should do the job, and I'll never have to worry about a flat battery after leaving the van for a few weeks again. Worth it?
Any problems with this approach?
In an ideal world I'd go and start the van up and run it for a while every week or so if I'm not using it, but reality is I'm rubbish at doing that sort of thing.
“As I understand, this WILL NOT allow the starter battery to charge from the house battery bank, correct?”
I don’t have one, but I’ve been reading specs on this and others. According to specs that I’ve seen: correct.
“I'm thinking of putting a small solar panel and cheap PWM (or cheap MPPT) and having them connected solely to the starter battery.”
I do this now, as I do not have a house system yet.
The dark winter months just don’t have enough sun to let a small system work well enough, but if that is not where you are and you are careful where you park (leaves, bird droppings, dust, shade, etc), then it might work — it works for me in the summer.
If you do go that way, I wonder whether it may be better to just get one full solar setup with the MPPT charger on the starting battery and an appropriately sized/capable DC to DC charger from the starting battery to the house battery so that the starting battery is prioritized for charging and starting during storage while still keeping the house batteries fresh when there is enough sun, and no need for a high amp relay. But, be careful that the Dc to Dc charger isn’t so big that it ruins your alternator.
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In cold weather (I’ve started cold from <-20F, but it’s not fun), my 7.3l diesel needs full output from both batteries (especially after heating the glow plugs!) so I’m designing my system to keep the starting batteries charged and to even provide a boost from the house batteries if I need it.
downhiller
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I've just stumbled on this product:
sterling-power.com
Not cheap, but does two-way DC-DC charging between van battery and house battery.
If it had bluetooth and/or a more visually-appealing (and cheaper) remote I'd be very tempted.
2023 Model 12V to 12V DC to DC Chargers 10A | 15A | 20A | 25A | 40A | 70A | 120A models + Remote Control (optional)
12V to 12V DC to DC Chargers 10A | 15A | 20A | 25A | 40A | 70A | 120A models - E-Marking New BB1225 - video - available now New BB1210- video - the benefits of 10A current limiting - charging portable power banks 10A | 15A | 20A | 25A | 40A | 70A | 120A | 200A models available now. We can ship...
sterling-power.com
Not cheap, but does two-way DC-DC charging between van battery and house battery.
If it had bluetooth and/or a more visually-appealing (and cheaper) remote I'd be very tempted.
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