Converter/ solar feasibility question.

[JiminDenver]

I didn't want to hijack Muddys thread so here it is.

I accidentally left the converter on when I hooked up the systems this trip and it got me thinking. Since the trailer is plugged into the big inverter and the solar, could the converter be used a few hours a day to keep the trailers battery up instead of switching the panels around?

Now I know that even all 3 of my system for 50a wouldn't cover, at least at first. The 8-D would have to help out. The trailers battery never gets that low and on a day like Saturday when we had 12 hours of brilliant sun, the 8-D would have time to recover.

Soooo if I am just to lazy to switch the systems around, is it feasible?

[RJsfishin]

Sorry,
I missed the 2 banks of batts.
Yes, that's one way to do it, surely not the best.
I would think just a small switch connecting the positives for the time needed. Sure works good to keep my starting batt up.

[JiminDenver]

RJ

It is just a feasibility question and I wouldn't be creating a loop. Having the solar on one bank with a big inverter and it would see the converter charging a smaller bank as just another load. there would be losses and it wouldn't be the best way to keep the trailers battery up as it wouldn't get back to full daily.

So feasible? Yes Will I ever do it, probably not.

Now to get back to figuring out how to run a small air conditioner off of the solar. 😉

[BFL13]

RJsfishin wrote:
Is the OP above the same as saying,....
I have some cloudy days, so batteries are slowly going down a little more every day. So rather than add more solar (move panels) I'll just use my inverter to power my converter to bring the batteries back up.

Ok, I must have misunderstood it completely, because we all know that don't work.

My understanding ( ? ) is that he has two separate batteries of different types and one solar set- up that he swaps back and forth to one battery at a time. To save swapping over work he wants to charge one battery with a 120v powered charger or converter powered from the inverter attached to the other battery that is getting the solar.

It is not "efficient" but saves work and he has tons of solar so he doesn't care if it "wastes" some in order to save the work.

I gather the solar is not arranged yet to use a big switch to do one or the other or both, because it is still all portable, and the batteries are not in the same location so they can be both wired to that switch.

[RJsfishin]

Is the OP above the same as saying,....
I have some cloudy days, so batteries are slowly going down a little more every day. So rather than add more solar (move panels) I'll just use my inverter to power my converter to bring the batteries back up.

Ok, I must have misunderstood it completely, because we all know that don't work.

[BFL13]

With two battery banks, I found it worked best to have two separate solar set-ups one for each. I had the two T-1275s on my 130w PWM, 12v set and the four 6s on the 230w and MPPT Eco-W.

The Eco-W is not really able to handle the T-1275s with their high voltage demands (similar to the Screwy 31 situation) but the Solar30 could do the T-1275s.

The Solar30 went to the set Vabs (max of 15v) and then stayed there the rest of the day, but the Eco-W which can be set even higher for Vabs, drops to its Float voltage immediately upon reaching Vabs

The problem there is that the max Float setting is 14.5 so if you want the higher Vabs to stay on the rest of the day, you can't just make your Float setting the same as your Vabs.

However the 6s did get to baseline SG by dark when the Eco-W got them to 14.8 and then dropped to 14.5 for the rest of the day.

It took a while at 14.5 though, so the sun has to be up long enough. A necessary marker for whether the 6s would get to baseline SG on the 14.5 was that the Trimetric has to show the AH count going "over" past zero into positive by about 10AH or so. Reset the AH counter at dusk.

(Indicates gassing at very high SOC more than the 4% allowance Trimetric uses for that--which Trimetric explains in the owner's manual that efficiency goes out the window at very high SOC and the 4% works for the whole range as a good enough average)

BTW the usual story that 6s need over 15v to reach baseline SG seems contradicted by the above experience. IMO this is because on solar the 6s were doing shallow cycles like 80-99 but when doing deep cycles like 50-90s the whole SG thing changes. One drop to 50% will bring the SG "into the red" and getting back up from there is a hard slog so that is where the 15+ v comes into play.

When I sold the 12v set and banked the two T-1275s with the four 6s all on the Eco-W, the 6s got done ok but the T-1275s did not and what's more, the 6s were overdone, losing water while the set-up was still trying to get the T-1275s up to speed. Classic case of mixing different batteries in one bank.

The OP's idea would be fine for a short period of camping like a couple weeks but for a "seasonal" of months you would want to go with separate banks each with its own solar set with a controller that has the right set points for the batteries it is on.

[JiminDenver]

Thanks guys

This was just a question of feasibility and I know it isn't efficient. We have a Parallax 7300 series converter that even powered by the generator isn't the best way to get a charge. The Eco-W treats the batteries better with it's 3 stage charging and adjustable voltage. I have been following BFL's lead and keep the float voltage up while camping and the batteries seem to be fine with it.

Why would I do it outside of pure laziness, the only reason is if I had to leave the trailer and didn't want Honey to have to mess with the panels. There would be other ways to handle it but this would be just one scenario that would be possible. Thanks to BFL13's testing I know it is feasible, just not the best way to deal with it.

[Golden_HVAC]

While it 'can' be done, the inverter is going to take in say 12 amps for a 6 amp output of the converter. So if you can deal with that in-efficiency, then all is well. Yet it is much more energy efficient to run a #8 wire between the two battery banks, and then turn on a switch when you want the 8D batteries to charge the smaller ones from the solar system.

Fred.

[RJsfishin]

If I understand it correctly, answer is no,......like spinning your wheels. That inverter sucks,.....you much better moving your portable panels for maximum efficiency.

[BFL13]

Yes it is. A while back we had a thread going about using a "remote power supply" to plug the RV (that had no battery) into. Sort of a little trailer with its own battery bank and inverter with solar on it too.

I ran a backyard test of how that would work so the RV with no battery could get its 12v from its converter. IIRC it "cost" about 6 DC amps draw on the remote bank above what any rig 12v draw was. So the solar could keep up with that in your scenario even to charge its battery. Of course the battery would have to be smaller than the remote bank and not take too long to be tapering its amps to something less drastic.

I also tried just using a 2amp trickle charger on one half of my bank powered by inverter on the other half. It made the inverter draw 3 amps. This was no problem for the solar. Less drastic for amps than the converter which cannot be "dialed down."

I was thinking of running a trickle charger for the truck battery or one of those deals with a MH that has solar on the house but nothing on the engine batt. Just fooling around, but it did work.

This all came from a member here who was doing something like that but ran a long 12v line to the rig from his remote power bank. To avoid that long 12v wire we (ISTR mena was in on this) were trying the converter option.

[westend]

Jim,
If I'm understanding you correctly, I believe this falls under the "conservation of energy" laws. The converter has an inherent inefficiency so your solar system, alone, should get more charge into the batteries than using the solar and powering the converter.