Can I run two charge controllers off my solar panels, one to charge AGM and one to charge my starter battery?

Aldenso

Member
I've done a bunch of googling but haven't found anything, I'm sorry if this has already been asked...

Can I run two charge controllers from my panels, one to charge my AGM batteries, and one to charge my starter battery?

I'm asking because I have an Espar aux heater that I plan to use during the winter here in Canada. I've read about re-routing the wiring for the Espar to the house batteries, but see that it takes 10+ hours to do, plus I think it's over my head. I'd rather spend $20 on a charge controller and set it to charge my starter battery during the day, hell, I'd pay $100 to avoid 10 hours of frustration.

Can I just get some Y connectors before my AGM charge controller and add in another charge controller?

I guess alternatively I could get an AGM starter battery and wire it in to my bank, but that'll be a bit more costly.

Thanks everyone.
 

aksotar

2017 4x4 144 Cargo
Where are your heater and house batteries that you think that it will take 10hrs to run a line from your espar & controller to them or your 12v fuse block for your house batteries ?
you'll have to run a 12v line from the fuel pump to inside no matter which...
you really don't want to wire it to your starter battery...
Winter sun up north is short and low angle, let alone having to deal with ice & snow buildup... you don't want to drain your starter battery with the hope that your panel can charge it back up... esp when cold and maybe snowing for days...
 

Aldenso

Member

Vanski says he's done it several times and can't do it in under 10 hours. He puts single pole double relays (I'm already lost) as follows, t15, d+, heater, aux coolant pump, interior hvac blower motor, etc.

I have attached his wiring diagram.

Does the Espar not automatically stop working once low voltage is detected? So wouldn't I be able to just run it until low voltage, then just fire up the van/let the solar recharge the battery?

Also FWIW, I'll mostly be spending time on Vancouver island in an area that only rarely sees snow, though it is rainy almost always. Average winter temperature is around 9*C or 48*f.
 

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RVBarry

2023 AWD 170 DIY CamperVan
I don't see why it wouldn't work, except that if there's not much light, lower voltage could cause one or both not to stay on.
Putting panels in series, instead of parallel, will raise the voltage... Keep it well under the rating for EACH charger.
Note series can cause complete loss of charging if ANY panels are shaded.


You could also get a small solar panel charger and leave it on the dash.

There's various sizes; adjust based on needed power, as well as expected efficiency losses due to winter and poorer glass transmission.
 

Aldenso

Member
I don't see why it wouldn't work, except that if there's not much light, lower voltage could cause one or both not to stay on.
Putting panels in series, instead of parallel, will raise the voltage... Keep it well under the rating for EACH charger.
Note series can cause complete loss of charging if ANY panels are shaded.


You could also get a small solar panel charger and leave it on the dash.

There's various sizes; adjust based on needed power, as well as expected efficiency losses due to winter and poorer glass transmission.
Ok, I've normally wired them in parallel, but I think I'll do a mix to help with shading.

Those small panels are cool, but I think I'd get far more output from panels even if they're split to two controllers. Plus when I'm driving I feel like that'll be harder to get into the sun whereas the panels will have better coverage.

The controller basically limits overcharge, right? So I believe once the starter battery is fully charged it'll only charge the AGM batteries.
 

RVBarry

2023 AWD 170 DIY CamperVan
Those small panels are cool, but I think I'd get far more output from panels even if they're split to two controllers.
Hi, the question isn't how much power you can get, it's can you get ENOUGH?
The diesel heater won't use much, just a fuel pump and smallish fan.
Plus when I'm driving I feel like that'll be harder to get into the sun whereas the panels will have better coverage.
When you're driving, the alternator charges the starter battery.
The controller basically limits overcharge, right?
If it's set for the correct battery type.
 

Aldenso

Member
Where are your heater and house batteries that you think that it will take 10hrs to run a line from your espar & controller to them or your 12v fuse block for your house batteries ?
you'll have to run a 12v line from the fuel pump to inside no matter which...
you really don't want to wire it to your starter battery...
Winter sun up north is short and low angle, let alone having to deal with ice & snow buildup... you don't want to drain your starter battery with the hope that your panel can charge it back up... esp when cold and maybe snowing for days...
I'm reading and re-reading the thread I linked to you, and now I'm thinking it takes him 10 hours because he only has the booster. I've got the full on aux heater, so I think it's actually going to be far more simple than I previously thought.

I think I just would need to reroute the espar fuse under the seat and the fan/pump fuse under the steering column.
 

autostaretx

Erratic Member
The current from the panels will take the path of least resistance.
So there's almost no telling where the panels' output will go, given two controllers feeding two battery banks.
I suspect it will first go to the flattest battery. That controller will "steal" the panel's output.

Then there's the "what kind of controller?" question: MPPT or MPW?
The MPW is the simplest ... it's pretty much a switch (with throttling) between the panels and batteries.
The MPPT, on the other hand, will be trying to optimize the panel's output ... so two MPPT controllers would definitely get into hissy-fits.

--dick
 

Aldenso

Member
The current from the panels will take the path of least resistance.
So there's almost no telling where the panels' output will go, given two controllers feeding two battery banks.
I suspect it will first go to the flattest battery. That controller will "steal" the panel's output.

Then there's the "what kind of controller?" question: MPPT or MPW?
The MPW is the simplest ... it's pretty much a switch (with throttling) between the panels and batteries.
The MPPT, on the other hand, will be trying to optimize the panel's output ... so two MPPT controllers would definitely get into hissy-fits.

--dick
Those are very good points and things I'll have to consider. I'd want to go MPPT to maximize charging since I will be in crappier light, but I guess they'd probably hate each other.
 

Onefin

Well-known member
I've done a bunch of googling but haven't found anything, I'm sorry if this has already been asked...

Can I run two charge controllers from my panels, one to charge my AGM batteries, and one to charge my starter battery?

I'm asking because I have an Espar aux heater that I plan to use during the winter here in Canada. I've read about re-routing the wiring for the Espar to the house batteries, but see that it takes 10+ hours to do, plus I think it's over my head. I'd rather spend $20 on a charge controller and set it to charge my starter battery during the day, hell, I'd pay $100 to avoid 10 hours of frustration.

Can I just get some Y connectors before my AGM charge controller and add in another charge controller?

I guess alternatively I could get an AGM starter battery and wire it in to my bank, but that'll be a bit more costly.

Thanks everyone.
The SunSaver duo is a small capacity, simple PWM charge controller that can split between two batteries, like a house bank and a starter bank https://www.morningstarcorp.com/products/sunsaver-duo/
I’m not certain this is the actual goal you wish to accomplish.....
 

autostaretx

Erratic Member
If you watch this video review of the SunSaver Duo, it (unintentionally) suggests a way to roll your own far cheaper:


When she shows the meters bouncing up and down as the controller sends current to one battery, then the other, the idea hit:
You could have a single MPPT or MPW controller feeding a (let's say) relay that alternately feeds one battery, then the other.
Say that it "flipped" once per minute. The MPW controller will merely adjust its charge rate for the battery it's connected to for that minute. (i'll cover MPPT below)

Hiccups/alternatives: since you probably have 2 different battery styles (flooded and AGM), the single controller would not be optimized for the "wrong" one. So you'd get/have to choose who would "win" ... either the AGM only getting to (say) 95% charged, or the Flooded occasionally getting a little bit "cooked".

So ... what if we move the relay to *before* two controllers? Thus each would see only the panels (or nothing).... they wouldn't get into hissy-fits, since they wouldn't see each other. There will be a few seconds of "controller adjusting MPPT" after each transition, but that happens when you've driving along a partially-shaded road, too. Increase the flip-time to 5 minutes to minimize that.

As a final "frosting on the cake", you could have the relay-flipping circuit check the batteries' states of charge, and adjust its "duty cycle" (percentage of time on one battery versus the other) to cover when one becomes "full" before the other (or the Sprinter running so that the starter battery is getting charged by the alternator).

fun...
--dick
 

Kevin.Hutch

2011 Mercedes 313 906
"Can I run two charge controllers from my panels, one to charge my AGM batteries, and one to charge my starter battery? "

The Question seems simple enough without going into the why and what alternatives, I see no problem especially when both the start and house batteries are AGM.

It would also offer the simplest way to overcome charging two dissimilar battery types with the correct charging algorithms.
 

aksotar

2017 4x4 144 Cargo
Those are very good points and things I'll have to consider. I'd want to go MPPT to maximize charging since I will be in crappier light, but I guess they'd probably hate each other.
what happens after 3,4 or 5 days that you haven't started your engine but have been using a heater, lights, recharging batteries, etc and it's been overcast and raining/snowing.... panel isn't fully recharging your starter battery every day... and you want to start your engine and it's cold out....
thats why I would never run aux stuff off my starter battery.... terrible weather conditions that make you use more power and the same weather gives you terrible solar conditions, not a good pair...
 

autostaretx

Erratic Member
I agree with Kevin .... if your two batteries were both AGM, then you wouldn't have to worry about simply paralleling them.

In the T1N days, if you bought the MB Auxiliary battery system, you had a choice of flooded or AGM.
If you bought AGM, they upgraded your starting battery to AGM as well.

--dick
 

Aldenso

Member
Alright, thanks everyone for the input.

I've done a bit more research about the conversion of the Espar to house battery and I was getting confused because most people were converting heater boosters to interior heaters.

I ask a few members from the old post who have the same set up I do (aux heater) and it's far simpler than the heater booster conversion. I will be converting it to run off the house batteries.
 

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