Solar charging the starter battery

[roving1]

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.

In 10 years of working with OEM design responsible engineers, tier 1 auto supplier QA people, and in house special problem solving teams while they work on OEM vehicles including diagnosing charging systems and other electrical gremlins not once has has anyone ever disconnected a battery to charge except to do A/B or A/B/A testing. This is a non-issue.

 

[vomhorizon]

Dont confuse PV module or array with mechanical generation. Its a solid state electric current maker dohickey.
It can be loaded & loaded, or left unloaded as long as desired.

Thanks. This is what I suspected as well. Now, if the MPPT will dial down or completely eliminate charge to the battery when it is fully charged or when it is being charged by another source that is boosting voltage (I guess this is akin to an offloaded PV), why would I need to disconnect the PV from the MPPT while fearing for some sort of malfunction in my OEM electicals? I'm just trying to understand the underlying mechanics here. A ton of folks here, and elswhere charge their starter and house batteries using solar suitcases when stationary. In theory at least, when the car alternator is charging the battery the MPPT, a regulated source, should sense that voltage and back off. Is there something that I am completely overlooking which would be a cause for concern here?

So in my set up, in the best case I just keep the PV and MPPT wired in for good. Just run it that way and trust that the MPPT will back off. This is how a few folks are running on this forum and even here on this thread (and elsewhere as well). In the worst case, I just disconnect the anderson plug connections until I park and need to charge when stationary (this essentially means that I have a portable (suitcase) system that is only connected when stationary but one that is permanently wired so it doesn't use up room inside. I fail to see how this is tinkering with my OEM electrical system to a point where I risk damaging my electronics unless I do something stupid (like connect PV directly to battery or not fuse properly etc). In effect (though slightly different) a Red Arc DC to DC system that is solar enabled is also capable of managing two different charging sources and even charging the house battery via both concurrently.

 

[dreadlocks]

electrons are electrons, if both supplies are of equal voltage they will supply the loads evenly.. this is the whole basis of batteries in parallel.

The driving reason to disconnect devices if they are intolerant to eachother, if you have a shore charger that does a high voltage equalization charge they can get absurdly high so they suggest plugging it directly into an isolated battery so anything not tolerant to that high voltage wont go poof.. for our uses such charges should be supervised, and done at home, after checking all fluid levels and opening everything up for ventilation, and pulling the master disconnect.. but most all devices can take an EQ charge voltage in an automotive system, the thing is when you start using battery chemistries not used in auto industry with specialized chargers for em..

otherwise most systems can be easily designed to cope with all chargers going at once, worst case they drop into float early because each thinks the current is low enough the battery is charged.. there's also stuff like victron can use fixed absorb times or coordinate charge phases with each other to overcome such issues.

 

[john61ct]

Yes a decent SC and panels are usually left connected to a lead bank 24*7*365 no problem

If you want to "pause" for some reason and have no convenient switch, tossing a blanket over the panels works fine.

 

[dreadlocks]

on fixed installs I still put anderson pigtail on the solar charger with locking retainer pins, just so I can unplug the panels and work on the solar charger or any wiring downstream without some hot wires dangling about, nobody likes to jam raw copper into something and have a spark either.. but thats just me, I gotta tiny lil compartment to work on electrical in, dont wanna be balls deep in there and have a blanket blow off the roof.

 

[broncobowsher]

OEM says to disconnect the battery before charging. There are so many different chargers out there they cannot control what you will try to use. There are some crap versions that are rather high voltage. If you dig up grampa's old battery charger, it may charge quick and fast with no regulation. Many decades ago a tow truck gave a quick charge to a 12V battery via a 24V booster set. Crap like that + some conservative engineers = the generic "disconnect battery". Not because it is always the case, just an oddity that could cost them warranty money. Same ones that tell you that to weld on a vehicle you have to remove (list of every electronic part in the vehicle) and store them in a room far away from where the welding is happening. Read the Ford Body Builder's guide, it's in there.
Trailer towing guide, don't tow with the rear tires of the tow vehicle off the ground, don't install a hitch directly to the axle on the vehicle. Stupid things happened in the past equal stupid warnings today. Every hair drier now has warning not to operate while in a bath tub.

There is ZERO issue charging from multiple sources. Years ago before the plethora of high output alternators people would rig up a double alternator setup. I know Ford, GM, and Ram offered this as a factory option very recently. Ram does it to power the factory Warn winch.
The charge controllers look at the system voltage and regulate off that. If the battery is charged and the voltage is up, it quits charging. Doesn't matter if it is the solar charge controller or the vehicle alternator voltage regulator, that is there job. That is what they do. They don't care if the battery if full because it is just full, or full because a different charger topped it off. It just sees full and stops charging. There is no way for a voltage regulator to see interference from another regulator and decide to just keep charging. They both see the same battery voltage. If one stops at 13.8V and the other goes to 14.2V, so what? Both will charge until the 13.8V, that one sees a full charge and stops. The other will bring the battery to the full charge of 14.2V.

There is one possible way to have a fighting charging system. If you decide to invent the wheel yourself and get a shunt style voltage regulator to dissipate excess energy and wire the solar directly to the battery. This charges flat out, no regulation. And once full the regulator starts burning off excess energy as heat via the shunt. Typical old motorcycle charging system. Add this to a standard automotive charging system with slightly different set points. You could get the shunt trying to burn off electricity as the alternator is still trying to charge. But this is just a horrible bastard of parts that is not used in solar. You do find this on the mini wind farm as a way to slow down the wind turbine when it is very windy and the battery is charged. Without the load the wind turbine could run away spinning too fast. The shunt is a load to keep the speeds down.

 

[broncobowsher]

The Engle 45 is the old ARB fridge. On paper it can cool 122F. When I say it tops out at 100F drop from ambient, that isn't an exact number. It's inside a truck, with a little sun load. Maybe 110, 115 drop? You are splitting hairs at this point. The true freeze runs 0°F (-20C). 140F in the cab is very easy to get, not even in the summer. Add in you also have a heater running, waste heat off the fridge goes into the cab. You are not going to keep a true freezer temps inside a vehicle in the AZ summer. Most every summer there are news clips of people cooking food on the dash of the car, fry an egg on the sidewalk. Inside a vehicle it is high 100s. 170F+ in a parked car and even at full power it will be warmer then it should be for a fridge.

But drive with the A/C on, all is good. Head to the mountains, comfortable with the windows down, all is good.

 

[john61ct]

Engel came first

ARB started out as a relabeler

 

[vomhorizon]

The Engel fridge has probably been around longer than ARB as a company.

 

[vomhorizon]

So when I was evaluating options for a single battery vs dual battery setup, I had reached out to a few lithium battery OEM's to see what their policy was for engine bay auxiliary battery (non starter) installations. Most of them didn't reply, or were extremely vague, but I did hear back from ReLION that they would fully warranty the battery if used as a deep cycle house battery in an engine bay setting. Just wanted to throw that out there in case someone wanted to know. On the Toyota 4runner (5th Gen) most aftermarket aux trays will have enough space to accomodate ReLION's Group 24 - 75 Ah LIFEPO4 unit.

 

[john61ct]

Note that does not mean that vendor has a better product.

Just that as a mass marketer / relabeler to consumers, they have realized how much stock people put into warranty

and built enough profit margin in to handle their projections of percent of customers that end up actually returning (very small).

IOW good business sense, not necessarily any technical superiority.

 

[vomhorizon]

Yeah I didn't imply any superiority. But if I were considering two equally priced batteries and wanted the assurance that if something were to happen, I would be supported with a replacement then I'd naturally go to the one OEM that honors their warranty for my specific application. Similarly, if I were not using the battery in the engine bay, I'd consider going for the one that offered the longest warranty and had the best customer service based on user feedback. Assuming both could meet my needs of course.

 

[john61ct]

Let's say a given top notch LFP bank would last 8000 cycles or 40 years calendar life

if cared for meticulously, including average 20°C ambients (EoL 70% SoH)

The same bank, same care in a much hotter environment might "only" last an average of 2000 cycles or 8 years calendar life.

But that last performance might well be just fine for most consumers.

While others with more options may still be horrified "the engine bay will **murder** your pricey pack!"

Both valid POV.

The wild card is, so many variables involved no way to quantify the relative impact of the various care factors.

 

[john61ct]

Since I do not traffic in "drop ins", I select the cells from what I know to be the top quality makers.

Their main customers are EV manufacturers, and the military, really have no interest in individual consumer market, lucky we can even buy them at all.

I pay zero attention to customer service - there is none, much less expecting warranty policy to ever be honored, since shipping back to China costs more than the cells are worth.

I am not claiming everyone should follow this path, just laying out what **I personally** think will lead to maximum value for money

as food for thought.

 

[vomhorizon]

Let's say a given top notch LFP bank would last 8000 cycles or 40 years calendar life

if cared for meticulously, including average 20°C ambients (EoL 70% SoH)

The same bank, same care in a much hotter environment might "only" last an average of 2000 cycles or 8 years calendar life.

But that last performance might well be just fine for most consumers.

While others with more options may still be horrified "the engine bay will **murder** your pricey pack!"

Both valid POV.

The wild card is, so many variables involved no way to quantify the relative impact of the various care factors.

Great points as always. So much depends on one's budget and how one is expected to utilize that both scenarios could look attractive to one and a deterrent to another. I guess with LIFEPO4, drop in, it also comes down to what you can fit in a given space in the engine compartment.