Maintenance & Restoration

ThomasC · 03-20-2021, 10:23 PM

Quote:

Originally Posted by mariaandskip

I'm still in the process of designing our system so any input is appreciated.

When we were living on our boat we had an engine battery and 2 house batteries. I replaced the factory alternator with a high out put alternator without the built in regulator. Then I installed a standard regulator to charge the engine battery and a 3 step regulator to charge the house batteries. I used real heavy (no 2 I think) wire for charging the house batteries. There were times that we went a week without running the engine to charge the batteries.
I was thinking of replacing the house battery with a lithium and putting an additional lithium "house" battery in the van. This way it gets charged when we are driving without the trailer behind us.

I'd appreciate any thoughts/feedback on this

I had that idea. Put some of your battery bank in your TV and maybe even a solar panel on the cab or the cap. The problem with the idea is how to connect the two systems together when they are at different charge levels. It is a huge no-no connecting batteries in parallel when they have different voltages. The batteries try to equalize instantly and huge amounts of current can surge though the system. In other words sparks will fly.

John in Santa Cruz · 03-20-2021, 10:27 PM

yeah, parallel batteries should be RIGHT next to each other and connected with very short very heavy gauge wiring, and kept that way from new til end of life.

mariaandskip · 03-21-2021, 10:59 AM

That's fixable

Lynn Eberhardt · 03-21-2021, 11:24 AM

In practice, it's not any different than re-connecting the TV after a few days of boondocking while you've had the TV out sightseeing. The voltage difference is not great enough to create a huge surge. I've been doing the two battery thing for years.

mariaandskip · 03-21-2021, 11:28 AM

That's fixable reply was to a few posts back.
I'm glad I posted this question. I should have realized the problem when connecting the 2 batteries with unequal charges. That would have been quite a supprise the first time I hooked it up. Maybe even a battery melt down. Couldn't that current flow be controlled $$$$$ ? Is this getting too complicated for a KISS adherent?
I appreciate the input, that could have saved me an expensive lesson.

computerspook · 03-21-2021, 05:51 PM

I thing I have done on a couple trailers where I needed to get charges on the road and the trailer connectors were not that dependable was to put in an online switchable boost charger. That is a 1 or 2 amp charger that takes in a bit under 3 amps and makes sure it is the right voltage for charging the battery. If you are going any distance with a tow vehicle that really will give you a nice charge. But that was with a slightly smaller battery. But they have boost chargers for other amperage.

One key is clean contacts on both ends of the connection. And the ground is critical. A lot of 7 flat pin (RV) hook ups use light gage wire for the ground. I use 10 or better. And most run the ground wire to the front of the TV on light gage wire. I connect it to the frame right at the connector. Like a foot of wire between the connector and the grounding location. Then I corrosion proof the ground connection. That will work miricles.

ThomasC · 03-22-2021, 02:38 AM

Quote:

Originally Posted by ThomasC

I had that idea. Put some of your battery bank in your TV and maybe even a solar panel on the cab or the cap. The problem with the idea is how to connect the two systems together when they are at different charge levels. It is a huge no-no connecting batteries in parallel when they have different voltages. The batteries try to equalize instantly and huge amounts of current can surge though the system. In other words sparks will fly.

I was speaking from ebike experience where I run parallel packs. The pack voltage is 84 fully charged and if you are off a few volts when you connect them the surge can get you in trouble.

Now in a 12 volt system the voltage differential will be less, maybe a volt, so there will be a smaller chance of a problem. This thread is turning into the differences of opinion that occur in the ebike forums when talking about paralleling packs. I don't follow conventional wisdom on the ebike forums and have been criticized for some of the things that I do.

Perhaps I was being overly conservative here but we have to remember there is a vast difference between working with a lead acid system and a Li-Fe-ion system because of the BMS that is built into lithium batteries. Lithium batteries have the potential to transfer huge amounts of current very quickly compared to lead acid setups.