Charging battery bank via solar and alternator simultaneously?

brianjwilson

Some sort of lost...
Sorry if this has been answered, I've searched online and read several theories without a definitive answer.

I'm going to describe my proposed setup below. In the end, I'm trying to figure out if having the alternator charging the same battery bank as the solar is going to be self defeating is some way. In other words, will the vehicles voltage regulator see high voltage from the solar and not supply a charge? Or will the solar see alternator voltage and not supply a charge? Will both systems be confused?


Vehicle and proposed setup below;
-2015 Toyota Tacoma
-2015 four wheel camper (on order)
-3 new odyssey AGM batteries. Starter battery in factory location, two aux/camper batteries under/behind rear seat.
-Blue sea ACR 7622 under hood, start isolator wired, manual override switch in cab
-3 x 100 watt renology panels mounted on camper roof
-Blue sky 3000i MPPT controller mounted in camper
-A + and - post mounted in the camper battery compartment, large gauge wiring connected to aux batteries under rear seat. (Battery compartment is in far rear compartment so I'm relocating under seat for battery weight distribution)

Relatively simple, right? My intention is that the panels would charge the batteries primarily. The need for solar and dual batteries comes from a 12v compressor fridge. So the thought was, during the winter months (very long in the Pacific Northwest) the alternator would provide a lot of the charging. Solar would assist and top off. I frequently move around a lot, rarely staying in a spot for several days. I Figured the blue sea ACR would simply connect and disconnect as needed, and I could over ride if desired. On a good solar day the ACR would connect both banks and charge all batteries. If limited solar charge is available I could manual disconnect the ACR and the two aux batteries take charge priority. But I'm wondering if there is any issue with voltage sensing with both charging sources. I feel like nobody ever discusses this, so I'm probably over-thinking it. I don't want to kill a bunch of new batteries though by somehow under charging them.

I appreciate any input. I've had a camper before, I've installed battery isolators and a lot of electronics, but solar is throwing a new component into the mix for me. I want to make sure I get it right, and have a little bit of charging over-kill for dark and rainy days. Thanks!
 

brianjwilson

Some sort of lost...
Again maybe over thinking. I suppose if the batteries are 60% state of charge, solar would be providing a bulk charge at lower voltage. The alternator (voltage regulator) would still sense this as low voltage and provide a bulk charge at the same time? I'm fine if the alternator kicks off the solar, I just don't want it the other way around of course.

I read some of the thread regarding the Ctek controller but it only confused me more. I don't want to mount the solar controller in the truck. The FWC solar wiring is already fairly small and I would have to add much larger wiring from the roof, all the way to the battery, just to get a decent voltage to the controller. Then I would end up with four large wires, more holes drilled, two different connectors in the bed of the truck etc.
 

dwh

Tail-End Charlie
It's like an air tank with multiple compressors, and each compressor has its own pressure switch.

Let's say the truck voltage regulator is set to 14.5v and the solar is set to 14.4v. As long as the battery voltage is below 14.4v, then both power supplies will be switched on and can potentially supply their full amperage to the "12v bus" (how much amperage they will actually supply, will depend on the resistance of the battery and wiring).

When the batteries (and thus, the 12v bus) reaches 14.4v, the solar charge controller will stop supplying power to the bus, but the alternator will continue to do so until the bus voltage reaches 14.5v, and then the voltage regulator will shut down the alternator.


The ACR will tie the batteries when the voltage on either side rises to 13.5v. So if your solar is charging the aux battery, and it has pushed the aux battery up above 13.5v, then the engine battery will be tied in. But it's already pretty much fully charged, so the majority of the power from the solar will still end up going into the aux battery.

Ultimately, all of the batteries (tied into a single bank/bus by the ACR) will rise to whatever the solar charge controller is set to - say 14.4v. The ACR will keep the batteries tied until the combined "bus voltage" drops to 12.75v for 30 seconds, then it unties (isolates) them.


Works the same way on the other side. Say it's dark and no solar. You start the truck. Say you started out with the engine battery resting at 12.75v. The ACR untied the batteries long ago. Your aux battery is down to say 12.0v. You engage the starter, pulling down the voltage on the engine bus and burning maybe 1/5 of an amp hour from the engine battery. The voltage regulator sees less than 14.5v, so it turns on the alternator.

Within seconds, the engine battery has had the 1/5 of an amp hour recharged, and the engine bus voltage starts rising. When it hits 13.5v, the ACR ties in the aux battery (combining the engine and aux buses into a single bus). Again, since the engine battery is basically fully charged (high resistance), the majority of the power from the alternator will flow through the aux battery. The voltage regulator will keep the alternator switched on until it sees the bus voltage rise to 14.5v.


In reality, it's a very fast up and down. The battery voltage rises to 14.5v, the voltage regulator shuts down the alternator. But if the battery was not fully charged, then it only had a "surface charge" of 14.5v, which dissipates into the electrolyte, and the battery (bus) voltage drops, and the voltage regulator turns the alternator back on. Rinse and repeat for however many hours (8-36) of drive time it takes to get the aux battery truly fully charged off the alternator.

Voltage regulated alternators don't do a true "bulk stage". They are constant voltage power supplies, not constant current. So they basically just do one long absorb stage at whatever voltage - 14.5v in my example here. They are designed to power the accessories and headlights. They aren't designed to be good battery chargers. Why would they be, when the only battery charging they normally have to do is to replenish that 1/5 of an amp*hour that got burned to start the truck?

But even so, with big enough wire, they can do a pretty good job of charging, because they can supply a lot of amps - IF the resistance of battery+wire is low enough to allow a lot of amps to flow. But as the voltage of the battery gets up above 14.0v, the resistance gets pretty high, and so even with a million amp alternator, only a few amps might be flowing.

Which is the reason for DC-DC chargers like the CTEK. It sucks power from the engine bus at whatever voltage, then kicks the voltage up and uses it to do a constant current bulk stage. But a DC-DC charger is incompatible with an ACR - it's either/or, but not both. (How can it suck power from one side to deliver to the other side, when the ACR has tied both sides into a single unified bus?)
 
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4RunAmok

Explorer
My guess is that the alternator would immediately put voltage up around 13.5-14.5 volts, which would be sensed by the Solar Charge Controller, putting it in standby.

You can group your positive wires and negative wires at the panels, and just have perhaps a 10 Gauge pair of wires run into the solar controller. Minimizing your run inside, but allowing you capacity to even add more panels later. The amount of voltage and amperage coming off the solar panels, 10 Gauge would be plenty sufficient. 10 Gauge can handle 30 amps out to 25 feet. You won't be getting anywhere near that from solar panels.
 

dwh

Tail-End Charlie
I suppose if the batteries are 60% state of charge, solar would be providing a bulk charge at lower voltage. The alternator (voltage regulator) would still sense this as low voltage and provide a bulk charge at the same time?

Yes, that's exactly how it works.

Except that the alternator won't be supplying a "bulk charge". It will be switched on, and it will supply however much gets sucked out of the bus in order to hold the bus voltage at the set point. But how many amps that will actually be....depends on the resistance of the battery+wiring.


I'm fine if the alternator kicks off the solar, I just don't want it the other way around of course.

They each monitor the bus voltage and each do their own thing depending on the bus voltage. They don't butt heads.
 
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dwh

Tail-End Charlie
My guess is that the alternator would immediately put voltage up around 13.5-14.5 volts, which would be sensed by the Solar Charge Controller, putting it in standby.

Most charge controllers don't have a "standby".

If it's a "3-stage", then it will bulk to some set point, say 14.4v, then drop the voltage to do the absorb stage - usually 14.2v - and hold it there until the amps flowing drops below a certain point - usually 1a-3a depending on who made it - then drop the voltage again and hold it for a float stage - usually around 13.6v.

The alternator won't immediately raise the voltage of a low aux battery to full charge voltage. It takes time for the aux battery voltage to rise. During that time, both the alternator and the solar will be available to supply power. Once the aux battery voltage (and thus the voltage of the combined 12v bus) hits the bulk stage set point of the charge controller, say 14.4v, then the solar will lower its output voltage to say 14.2v and if the alternator is holding the bus voltage above that, nothing will flow from the charge controller, and it will see that as a "full battery" and drop its voltage to 13.6v and just sit there.
 

dwh

Tail-End Charlie
The ACR will tie the batteries when the voltage on either side rises to 13.5v.

CORRECTION: I had a feeling I was remembering that incorrectly, so I just checked it. It will tie the batteries when the voltage on either side hits 13.0v for 90 seconds, or 13.5v for 30 seconds.
 

brianjwilson

Some sort of lost...
Thanks guys, just needed some confirmation after reading some poorly written "theories" about it. Nobody ever talks about it so I figured it wasn't a big deal. I think reading that ctek manual convinced me it was an issue too! haha

I believe the FWC wiring is only 10 gauge from the roof to the electrical compartment. Which should be fine for a shorter run of solar, I just didn't want to try to run it all the way into the cab for something like the ctek controller. I think I'll probably install a combiner box on the roof with a positive and negative bus for the panels, and use the existing FWC wiring into the charge controller. I see a lot of people leaving excess wiring on their panels because cutting the wire voids a warranty, and then using different plugs and adapters. I would prefer to hack off any excess and minimize unnecessary connections, myself.

I'm sure I'll have more questions in the future about settings on the blue sky solar controller and how to keep the odyssey batteries happy.
 

dwh

Tail-End Charlie
Odysseys are simple.

Bulk to 14.7v.
Absorb at 14.7v for 8 hours or until amp flow drops below half an amp (whichever comes first).
Float at 13.6v.

But of course, with solar only, you might never actually finish an 8 hour absorb stage before the sun goes down.
 

dwh

Tail-End Charlie
Not likely 8 hours! I did see that they like 14.7v but didn't see how long yet. Sounds good!

Also not likely doing it with an alternator - especially considering that the voltage regulator might not even go up to 14.7v ever.

Which is why Odysseys apparently have issues...

Some reports around here of them degrading to where they have a full-charge resting voltage of only 12.6v or less (instead of the 12.85 that is specced).

Odyssey does have a recovery procedure. Drain it fully, then recharge at C*.4 (40 amps constant current charge rate per 100ah of battery capacity).

Apparently several people around here have been told to do that by the Odyssey techs/engineers. Odyssey of course, sells a special charger that can do it.

No explanation of why that happens. Since lead-acid doesn't develop a memory like NiCad, the only thing I can think of is that they are experiencing their own "starved electrolyte AGM" version of electrolyte stratification.
 

brianjwilson

Some sort of lost...
I have read that about odyssey batteries as well. Which is why I'm hoping that tying all of the batteries together will allow the alternator and solar work together. I haven't looked at the truck's charging voltage but Im assuming it's right around 14v max. If I'm out and about, hopefully the alternator would do the bulk of the charging and the solar would bring the bank up to 14.7 for a period mid day.

I don't know what FWC is using for a coverter/charger these days either. Their website is horrible and not frequently updated. They change suppliers of major appliances and don't let anyone know. I found out through other forum members that I won't have the low draw furnace they have been promoting and using for years. Frustrating to say the least.

Due to my job, the truck is stationary in my garage 16 days straight every month. If the camper is on the truck, I ought to be able to use a good charger that would bring them up to 14.7 for 8 hours before keeping them on a 13.6v float. The ACR should keep everything tied together and charged...?
 

dwh

Tail-End Charlie
I would assume a 2015 truck will have a computer controlled voltage regulator which will adjust voltage based on several variables. If it's temperature compensated as well, it might go to 15v or more in the cold. So I think that "14v" assumption is probably not valid.

Certainly a good shore power charger would keep them in top shape - as long as it was programmable or was made to do an Odyssey charge profile. No way would I want to leave that job to a regular ol' RV converter, which are notoriously crappy and dumb.
 

mm58

Observer
Just food for thought, but a simpler and less worrisome design would be to have a relay in between the solar system and the alternator. The relay coil would be energized by 12v ignition ON voltage. So then the battery bank would normally default to solar charging, but when ignition and engine is on, charging comes from alternator. This is what I am doing on my vehicle.
 
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