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Old 02-04-2017, 03:14 PM   #104
israndy
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Default Re: Trickle Charger for Sprinter Batteries

If left alone the chassis battery will never need bulk charging. Maybe if you leave the headlights on. It is used to start the vehicle and then it begins to charge.

So your car battery is sitting at 12.9 volts, almost full

Your house battery is depleted at 11.9 volts, ready for a full charge

If a 3 or 4 stage charger is let loose it will sense the voltage on the house batteries and decide what stage to put the charger into. At this point it will be bulk. So all the current all the time, floodgates are open. Unless you have a battery monitor it cannot know how many amps need to go back into the battery so it has to test the voltage and see. Now combine the two battery packs. It sees there is 12.9 volts out there so it doesn't charge quickly, it goes into a slower charge mode and the batteries take days to charge. Or worse, the house packs start charging from the starter battery and drop it's voltage, so the charger reads that, and goes full bore. But the starter battery already is full. This high level of charge will boil away the chassis battery while the house batts are lapping it up. This arrangement will age the batteries quickly.

So we use a Trik-L-Start, or if you think you need it, an Amp-L-Start, say you have two starter batteries and 500 AmpHours in your house battery pack. Now I am not saying RV designers always are smart about charging. Until just a few years ago, they didn't even use multi-stage charging. Just used a relay that tripped when there was charge level voltage out there so everyone charged the same and isolated while the batteries were in use so you didn't kill the starter battery with your furnace overnight. And LOTS of RV batteries were replaced all the time. Batteries can be expensive, and we are learning to take care of this.

Now we are heading into the era of BMS monitored Lithium batts. This will be a whole new world.

-Randy
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Also a 40' Airstream Sky Deck, a 1999 Jeep Grand Cherokee, 2000 Honda Hybrid Insight, new 2013 Volvo C70 hardtop convertible
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