DC to DC charger or solar instead? (1 Viewer)

[SF1911A1]

Forgive me if this has been discussed, but I could not find anything by searching.

I was looking at how to power my dual battery system and would like to use a solar panel permanently mounted on the hood. I know that people have had bad experiences with the flexible panels on hoods, but all the posts I saw were at least two years old if not older. Many positive things have been said about the Renogy panels and they have a 100 watt flexible panel that will just barely fit my hood (99 LX470). If I run it through the victron charge controller, will that keep both batteries topped off at all times and negate the need for a dc to dc charger? I live in Houston so sun is not hard to find.

I was originally looking at the ctek dc to dc charger with smart pass, but that combo would run me about $700 and I’d like to avoid spending that much is possible.

Thanks for any input.

 

[e9999]

I imagine that the Victron is actually a DC to DC charger too.
Anyway, I don't know much about isolators and the like but I suspect it may not be quite as easy / foolproof as connecting the Victron to 2 engine batteries in parallel and nothing more. Both for the batteries but also for the Victron's sake.
Also, panels do lose a lot of efficiency when getting hot. So, the engine bay heat won't help there if they are hugging the hood.
On a related note, have you considered photoshopping a solar panel on a pic of your truck before you actually start gluing or screwing things on there, and see if you like the look? Cuz dang....

 

[SF1911A1]

Obviously this is an FJ cruiser, but the look is the same. Doesn’t bother me at all. I plan on attaching the panel to the vinyl just like this so that if I decide to remove it there is no permanent marks or holes. Engine heat I’m not worried about because the charging is for when the vehicle is off, if it’s less efficient while I’m driving I’m not worried about that. I forgot about the battery isolator, but I’m pretty sure you are correct that I would need one. Any other suggestions such as which isolator is best? I appreciate the feedback.

 

[drftsub]

Just as an FYI, this one will do both : Dual Input 25A In-vehicle DC Battery Charger

If you have solar input, it will prioritize that, if not, dc-dc charge.

 

[SF1911A1]

I like that, and they have an isolator so I can just keep the whole system with one brand made to work together. Thanks a lot.

 

[spressomon]

FWIW & FYI, we just did a ~4k mile trip over two weeks, which also was our maiden voyage with our new to us 2014 Escape 15A I've been modding. I installed a 6500w/400A LFP using Prismatic cells I assembled with a Sterling BB1260 for DC-2-DC charging of the LFP as well as isolating it from the two FLA starting batteries. The LFP and Sterling are mounted in a steel nose box on the front of the trailer (vented).

I'm using the default LFP charge profile but in addition to all the different battery types, et al, the Sterling can accept a custom charge profile. After first connecting the system I measured 49.5amps flowing at idle from the Sterling into the LFP array.

Electrical accessories in our trailer that depend upon the LFP + Sterling system to provide 12v & 120v: Xantrex Freedom X 3000w PSW inverter, microwave, Isotherm water heater (750w), 120v heated mattress pad, water pump and LED lighting. And, although we didn't take it on this trip (long story but suffice to say it will NEVER happen again ), I also have a couple espresso making devices that require between 500w and 1000w depending whether I'm just steaming or decide to take the Olympia Cremina for our daily espresso and cappuccino fixes, it won't be a problem as I used to run both on the 200A LFP that used to reside in my TrailTailor trailer and now is located in the bed of the HD2500...

The engineer I spoke to at Sterling, pre-purchase whilst in decision making mode, was incredibly helpful and answered every question I had with seeming authority.

Like some/most of the DC-2-DC charges operating off the pulling rig's alternator a non-lithium battery is needed to connect the Sterling BB1260 to if you are going to charge an LFP battery: Not a problem as both of my tow rigs, a 2007 Chevy HD2500 and my 1999 UZJ100, utilize FLA batteries in the engine bay.

 

[e9999]

SF, does your truck have a computer-controlled alternator? Cuz then I think you really do want to have a good DC to DC charger or you may not charge the auxiliary battery from the alternator as well as could be. If you go with a DC to DC charger and a separate Victron solar charger, I would also ask Victron what would happen if the Victron is set to a lower voltage charging like in float mode, say, and the DC to DC charger is cranking out more than that. The poor thing may get confused (or is that just me? ). Or generally speaking, check that the two devices respective cycles are compatible. One advantage of the dual input I imagine...

 

[drftsub]

FWIW , I believe @SF1911A1 has a 100, and my 200 which has a “semi smart” alt still works fine w the Redarc bcdc and charges my LiFePO4 battery from the alternator without issue (and the linked unit has a lithium charge profile).

 

[SF1911A1]

SF, does your truck have a computer-controlled alternator? Cuz then I think you really do want to have a good DC to DC charger or you may not charge the auxiliary battery from the alternator as well as could be. If you go with a DC to DC charger and a separate Victron solar charger, I would also ask Victron what would happen if the Victron is set to a lower voltage charging like in float mode, say, and the DC to DC charger is cranking out more than that. The poor thing may get confused (or is that just me? ). Or generally speaking, check that the two devices respective cycles are compatible. One advantage of the dual input I imagine...

drftsub is correct, I have a 99 LX so smart alternator is not an issue. For right now I'm just planning on using the setup for two optima batteries. I have a red top starter and yellow top for house.

Spressomon, Do you have solar in that mix at all or is it all based on the alternator? I’m looking to buy a camper in the next year or so and would likely build my own LiFePO4 battery bank (Jehu style) for it when the time comes. I’ve already run a 4 gauge wire from the house battery in the engine bay to the back of my LX. Would I be able to just connect the future battery bank to that wire (using a distribution block or something similar) to charge the entire bank?

E9999, the complication of the cycles you are talking about is a good example of why I would like to simplify the setup as much as possible. I could probably save a couple hundred dollars by using a victron and different dcdc charger and yet a different isolator. I like the ctek unit with smart pass, but the thing is ~$700. It looks like the redarc will do everything I want for about half the price of the ctek and I can also use their isolator for uniformity. What do you think?

I’ve heard of sterling but haven’t researched them much. I’ll check them out tomorrow and see if that’s a better option.

 

[spressomon]

SF1911A1, no solar. I don't have enough real estate atop the roof of our little 15' Escape to house ~800+w of PVs that it would take to keep the LFP happy when camped in one spot for more than a couple days. So, for relatively cheap I'll let the diesel idle for a couple hours...ditto for the 2UZ-FE when/if applicable. May add a 200w Merlin folding panel eventually...to augment when sitting for more than a couple days; but for now I have an extra 100w panel to keep the battery balancers in check while the trailer sits unused.

I used 1/0 from engine bay to rear bumper on both the HD2500 and the '99 UZJ100 using an Anderson SB175 and their Environmental Boot at the bumper end. FYI/FWIW, Joey aka WitsEnd makes a super slick powder coated steel bracket for the SB175 with the E-boot that made mounting it on the bumper of the HD2500 quicksilver. Check your anticipated current flow and round trip distance for best wire gauge recommendation.

Best price I found on the Sterling BB1260 (the also offer it in a 30A variant) was from ElectricCarPartsCompany.com where I purchased it along with all my LFP cells and drop in too.

 

[e9999]

800W? Geez.... Why so much?

SF, I don't know much about dual battery systems, so I picture the typical dumb isolator as being just a switch that disconnects the 2 batteries before the voltage becomes too low for the starting battery. But I wonder if there may also be the need for some sort of diodish one-way current protection to prevent odd feedback between the alternator and solar panel source. Don't know how that all works, though.

 

[drftsub]

But I wonder if there may also be the need for some sort of diodish one-way current protection to prevent odd feedback between the alternator and solar panel source. Don't know how that all works, though.

If the solar panel is run through the Redarc unit, it acts as a source disconnect to prevent this. I know you can achieve similar behavior with other controllers but this was one of the reasons I went with this unit on my build.

 

[e9999]

while we're on the topic of DC to DC chargers (besides the solar chargers), am I understanding correctly that with a proper DC to DC charger you could have the starting battery be at 12.6V, say, without alternator input (cuz the engine is stopped, say), and it could still charge the auxiliary one at higher voltages than that, say 14.4V for a while? IOW sucking power out of one to transfer to the other, regardless of which has the higher voltage?

 

[spressomon]

^ not on the Sterling: Charging is initiated when the house battery is at 13.2v or higher. 13.0v or lower for 240 seconds (adjustable) and charging stops.

 

[SF1911A1]

while we're on the topic of DC to DC chargers (besides the solar chargers), am I understanding correctly that with a proper DC to DC charger you could have the starting battery be at 12.6V, say, without alternator input (cuz the engine is stopped, say), and it could still charge the auxiliary one at higher voltages than that, say 14.4V for a while? IOW sucking power out of one to transfer to the other, regardless of which has the higher voltage?

No, the DC charger requires either solar or alternator input to do anything. It does not take power away from any battery at any time, engine running or not. When the engine is off and there’s no solar input, the DC charger is a paperweight.

 

[SF1911A1]

I just had a thought that might help anyone trying to figure this out down the road. When I first started researching dual battery setups I had a mental block that prevented me from comprehending the overall concept of a DC to DC charger. DC to DC does not mean battery to battery, which was my first impression. It simply means DC source to DC destination. DC source being the alternator or solar panel and DC destination being the DC battery or batteries.

 

[e9999]

why would the starting battery not be a suitable DC source? The only difference if the alternator is not running is that the voltage is lower. (And of course it has a limited capacity.) Are you talking about connecting the DC to DC charger directly to the alternator and not to the starting battery?

 

[SF1911A1]

No, you’re right that it’s connected to the positive of the starter battery. Maybe i’m wrong, but I see it as the dc charger basically stepping between the alternator and the starting battery at that point of input even though I guess technically it’s not. By connecting at the alternator input to battery one, it can reroute power to battery two once battery one is fully charged.

 

[e9999]

Well, it's not like the DC2DC can prevent the alternator from charging the starter battery if it's downstream of that battery.

OTOH, I suppose it's possible that the DC2DC could be configured (is that an available feature?) to wait to charge the aux batt until the starter batt is fully charged, but would that not usually defeat the purpose since I am guessing that one of the issues with DC2DCs is that they are limiting the charging current to the aux battery compared to what the alt can crank out, meaning longer charging times?

 

[SF1911A1]

It charges the auxiliary battery first then the starting battery. I think the starting battery charges at the same time just like normal, but the the dcdc charger charges each battery to higher volt. For instance, let’s say both batteries are optima and really want to be charged to 15V. The starter battery would recharge to the standard voltage that the alternator can do having nothing to do with the dcdc charger or auxiliary battery. Then once the auxiliary battery is topped up to 15V, the dcdc charger switches back to the starter battery and tops it off to 15V. The alternator is not capable of the 15v charge on its own, but it can recharge the starter battery to 14.6 or whatever it was originally designed for.