Solar charging the starter battery

[vomhorizon]

There is a good reason why it says disconnect before charging, and just because some do it does not make it right It can work fine doing that a dozen times but there comes a point when it says enough is enough and a 1000 miles from no where is no time to find out the hard way.

This was essentially why I started this thread. My understanding of this, so far, has been that two regulated sources can co-exist. At least this is what I've been able to gather from the information that is out there. I'll keep digging into this but I have yet to come across something that is definitive on this.

You can have multiple sources charging the same battery bank at the same time. Whether it is shore power, an alternator, a generator, solar panels, etc., it doesn’t matter. Connect them all. Run them all at the same time. No additional protections or switching of any sort are necessary. Chargers of all types are protected against reverse current flows and base their output on the voltage of the battery bank they are charging. When a battery is getting charged by any source, it’s voltage will go up proportional to the amount of current being fed onto that battery. In some situations where you have a particularly strong charging source, like an alternator or shore power, the high current fed onto batteries will drive the battery voltage up to the point that the solar charge controller thinks the battery is full. When that happens, the solar charge controller will temporarily stop charging until the voltage returns to a lower level.

https://amsolar.com/diy-rv-solar-instructions/edfaq

What happens when I have multiple charge sources charging a single battery bank? I get this question asked almost every day. "I have a battery charger, an alternator, and solar panels charging the same battery. Does it get overcharged?" The other worry that I hear is that the battery might get undercharged because one charge source sees the voltage of the other charge source and shuts off...
Lets take a typical scenario. We have a lead acid battery bank hooked up to a shore power charger, an alternator and solar panels. The recommended bulk charge voltage for the battery bank is 14.4 volts.

At the dock the boat is typically plugged in to shore power and the battery soon gets fully charged. So the worry is that if solar panels are running at the same time will they overcharge the battery because it now has two sources charging it. Well assuming there is a charge controller fitted on the solar installation then both charge sources, the battery charger and the solar system, are regulated. They read the battery voltage and are programmed to not allow it go beyond a certain limit, they are also programmed to go into float mode after a certain time or when the charge current reduces by a certain amount. So the battery doesn't get overcharged.

The alternator isn't normally running when the boat is also connected to shore power but if it is it doesn't matter. The alternator is also a regulated power supply and the program will limit the maximum voltage as well as the time spent at that voltage.

What happens when I have multiple charge sources charging a single battery bank

shop.pkys.com

So given above, and the fact that the MPPT is charging the battery, why would it continue to supply a set level of power to the vehicle's batteries when the alternator is doing so and thus the higher voltage? It is a regulated source. I'm just trying to understand the rationale as to why this would "damage my electrical" set up..

As far as disconnecting the battery before charging. Suppose I want to charge up my battery at a camp site or at home. I can't simply plug my AC charger into the truck? People here run all sorts of connections to do exactly this. In fact, NOCO even makes them and sells them.

 

[67cj5]

This was essentially why I started this thread. My understanding of this, so far, has been that two regulated sources can co-exist. At least this is what I've been able to gather from the information that is out there. I'll keep digging into this but I have yet to come across something that is definitive on this.

https://amsolar.com/diy-rv-solar-instructions/edfaq

What happens when I have multiple charge sources charging a single battery bank

shop.pkys.com

Well why not contact the company who made your vehicle, because depending on the electronic some models/brands are more tolerable than others, at one time it was ok to hook up small battery chargers of below 4Ah, and different batteries require different charging profiles, either way external charging systems are a very grey area even more so since cars are loaded with on board computers etc, stuff one of them up and it could cost more than the car is worth to fix it,

My Solution to this is to not connect anything to my vehicles electrics, and I have multiple power systems but they can all be charged via Solar or a generator and Charger or by AC hook up. I have 3 different DC forms of power and that does not include the vehicles own 12v system.

Having had vehicles fail and alternators die for no reason I can only put this down to charging them while the battery was still hooked up and I am not saying I am right But we need to ask ? why does it tell you to disconnect the battery before charging if it can be charged while still hooked up,

It's not a risk I am prepared to take.

 

[john61ct]

Thousands of vehicles keep the MPPT hooked up charging concurrently in parallel with alt output never heard of a problem.

Automotive chargers vary enormously in quality and failure modes are unpredictable, would not do that with them.

Could use one-way diode (voltage drop) or an automated switch of some sort if you were that concerned, but IMO not required with a quality SC.

 

[john61ct]

Usually a fridge is a big load for a small House system (under 3-400Ah)

Usually it runs 24*7, and the bank is sized to handle 3-4 days of all loads running without energy inputs.

160W of solar will give 50Ah per day, but only in ideal insolation conditions which is rare in many locations.

If you can only fit 100Ah and using lead, then you must track your Ah in/out carefully, when nearing 50% (actual, not mfg claimed) capacity

then choose between A sacrificing House bank lifespan

B turning off the fridge

or C using ICE charge sources.

But both limited space and having on demand ICE power, really implies going LFP,

no more murdering your lead, much faster acceptance so less ICE runtime, no need to get to Full at all, triple the usable Ah in the same space, should go thousands of cycles rather than hundreds if you're lucky.

But costly yes.

 

[vomhorizon]

Could use one-way diode (voltage drop) or an automated switch of some sort if you were that concerned, but IMO not required with a quality SC.

I was thinking of connecting the solar panels to the MPPT using an Anderson plug. This would simply allowed me to remove the solar panels and plug in a portable panel in case my truck was parked in the shade etc. I guess if it is ok to do so I could just as well manually disconnect the solar panels from the MPPT (pull out the plug) when the engine is running ( would it be ok to have them up in the sun when not connected?). But this should be a problem from what I read. MPPT is a regulated charger and can dial its supply down when the alternator boosts the voltage up. Once the car engine is shut off, the MPPT would sense that and provide the optimal charge based on what the PV is putting out. I'm not seeing the danger here to my electric system though this is what I wanted to initially clarify with others who have more experience with these things than me as I've never run solar and haven't run a fridge in any of my prior rigs.

Regarding the AC chargers NOCO makes an entire line of Genius chargers which it promotes with being able to charge your batteries when still plugged in. In fact, they even make an add-on that allows you to connect your AC charger to the starter battery through the OBDII port. I use one of those. Others run a different type of connector while yet others add a plug so that they can plug it in to a 20 Amp terminal at say a camp ground. I know a few folks who even have a weather proof AC charger permanently mounted in the engine bay to make plugging in easy. And they are built to allow for this (weather sealed etc).

 

[vomhorizon]

But both limited space and having on demand ICE power, really implies going LFP,

I don't want to put a Lithium battery in the engine bay. Based on my experience, folks in the 4Runner community who I know) have not had great success doing so. So the two realistic scenarios for me are:

- Keep my existing Group 34 Odyssey AGM Battery (starter) and add another Group 34 Odyssey AGM in the limited space available and connect the house battery via a Red Arc BCDC and solar as their 25Amp system has an MPPT so no need for an additional charger.

- Replace my existing Group 34 starter battery with a new Group 27 (92 Ah) battery and run a large solar panel to it to assist in keeping it topped off.

The first option would only realistically give me 34 Ah of usable juice to power a fridge. Should be good enough for 90% of situations but may require assist on rare occasions. It also requires that the battery be topped off the very next day to replenish the 20 or so Ah it would have consumed overnight.

The second option would give me about 45 Ah of usable draw - More than my house battery. Assuming that it is *SAFE* to keep charging the starter with solar even when the truck is running, this would do away with the need to put a second battery in the rig and the weight and cost associated with doing that. I'm torn between the two choices to be completely honest. I was planning to just run a single battery set up and use the Victron 70/15 to take care of keeping it topped up. But the issues brought up about how they interact with the vehicle's electric system has me thinking that it may just be a better option to suck it up and fork a few hundred more dollars and buy the red arc and a second battery.

 

[john61ct]

Another option

make a "hybrid" bank with two identical

top quality deep cycling lead batteries in parallel

Put an adjustable "battery saver" LVC between them, say you find you can go down to 12.8V and still have plenty of cranking energy. Have a good jumpstarter too for just in case redundancy.

While SoC is high, it is one big bank, you gain extra capacity both absolutely, and from Peukert's Law

When House usage has pulled SoC down to that cutoff point, now you have an isolated Starter batt no longer being drawn down, and

your separate House batt, just like you would've with the mainstream solution.

SoC monitoring gets a bit more complex, but maybe good enough to just benchmark your voltage levels.

You could keep them separate, and use an A/B switch, but then you lose the extra Peukert capacity.

 

[john61ct]

If you are nervous about solar while driving just turn it off

amps contributed compared to the alt will be insignificant anyway.

 

[vomhorizon]

If you are nervous about solar while driving just turn it off

amps contributed compared to the alt will be insignificant anyway.

Would it be fine to just pull the Anderson connector from the MPPT while having the solar panels sit in the sun on the roof top? I haven't ever used a solar charge system but just wanted to know if we could just leave these panels out there exposed to the sun without them feeding into the battery via a MPPT. This setup saves me the need to have a portable breifcase which takes up space and requires setup. In this case, I'd just plug in the anderson connectors and be done.

My plan is as follows -

- Run 4 Awg wires to the back of my rig and run them to a Blue sea fuse block. The live wire will be fused at the battery, and will feed into the fuse block via a breaker located adjacent to the battery up in the bay.

- Connect a Victron 70/15 MPPT and wire it through the fuse block by backfeeding power to the battery by the blue sea block (via a fused port from the 12 port fuse block)

- Fuse the solar panel at source and run a 10 AWG cable from it to the MPPT, terminating via an anderson connection so that I can easily connect and disconnect etc

- Connect the fridge to the fuse block via a 10 AWG wire and an anderson connector (or I could hard wire it as well)

So I have the option of simply disconnecting my solar panels from the system when the engine is running and re-connecting when it is not. I know members here don't see a need to do that but I guess it could be done for peace of mind.

 

[john61ct]

Yes, always disconnect the panels first before (optiinally) isolating the SC from the bank.

 

[vomhorizon]

Interestingly, the red arc DC to DC charger (with in built MPPT) can concurrently charge from both solar and the alternator.

 

[WVI]

HOBOTECH posted a vid a couple days back.
I forget what portable panel it is, but it is stout and comes with the older model controller that I believe would charge an auto battery.

 

[john61ct]

Any SC will charge an "auto battery" that is the mainstream default.

It's other more sophisticated banks where you need to be careful the SC meets its required profile voltages etc

 

[john61ct]

SC built into multi-function devices are fine for just keeping a starter topped up

but aren't near as good as even most cheap dedicated MPPT controllers

 

[vomhorizon]

How long do you think is it safe to offload a PV? I realize that the MPPT will do it anyways when the battery is fully charged up but is it ok to keep the PV disconnected from the MPPT for hours on in when the vehicle is being driven?