| DC-DC Chargers, how to be kind to your alternator and house batteries [message #364461] |
Thu, 03 June 2021 07:18  |
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RF_Burns
Messages: 2277
Registered: June 2008
Location: S. Ontario, Canada
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So we all know the 80/90 Amp alternator on the GMC is heavily taxed when the house batteries are low. We all have stuff more battery capacity for the house systems than the original coach came with. If the house battery is low and the chassis battery just started the engine, the alternator is taxed to the maximum current it can deliver.
We also may have different battery types for the house and the chassis, each requiring a different charge voltage/current (wet, Gel AGM, LiFePO4).
Enter the DC-DC Charger. This unit takes the chassis alternator voltage and converts it to the proper voltage/current curve for the type of house battery you have. It also effectively replaces the Isolator so you no longer need that. The output of the alternator is connected directly to the chassis battery.
Batteries should be charged with a limited maximum current, especially when low and charge is initiated. Unfortunately, an alternator is a fixed voltage with its maximum current limited only by its internal resistance and operating RPM. With a pair of golf cart batteries at low charge and all the other vehicle current draws, upon initial startup the alternator could be delivering well beyond its rated capacity... not good. The DC-DC Charger limits this initial current to the house batteries and sets the maximum charging current to a safe level. This reduces the load on the alternator to a safe level.
They come in various current levels and some have an adjustment to the charger current. For my LiFePO4 battery conversion I chose a 20 Amp model from Renogy. After receiving the unit I found the Low Current (LC) mode reduces the charge current to 1/2 its rated current. When I was initially looking at these, the LC mode reduced the current to 12.5%, so that is why I choose the 20 amp model. With the LC now at 50%, I would go with the 40 Amp model. So the maximum charge current to the house battery from the alternator would be 40 Amps. I could reduce this to 20 Amps by switching the LC mode ON.
The DC-DC Charger charges the batteries with the same multi-stage charging curve as your "Smart" charger in your house converter, so your batteries are charged in a proper way for maximum life.
https://nerdtechy.com/best-12v-dc-battery-charger
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.
1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that
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