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Old 09-20-2021, 06:51 PM   #1
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Default high amperage charging

So, this is continuing my questions from another thread on what the practical limits are for upgrading a vintage Dodge Roadtrek for high amperage charging into a large LifePO4 battery bank. On that thread I asked about upgrading the alternator system. Now, I am wondering about upgrading the converter to charge from the generator (I currently have the 45A PD converter).

It seems to me that it should be possible to get 150A at 14.4 volts for bulk charging out of the 2800watt onan. I am supposing that could fully charge a 300AH LifePO4 bank in just three hours of generator time. But maybe that is pushing the Onan's limits. Any thoughts?
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Old 09-20-2021, 07:12 PM   #2
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So, this is continuing my questions from another thread on what the practical limits are for upgrading a vintage Dodge Roadtrek for high amperage charging into a large LifePO4 battery bank. On that thread I asked about upgrading the alternator system. Now, I am wondering about upgrading the converter to charge from the generator (I currently have the 45A PD converter).

It seems to me that it should be possible to get 150A at 14.4 volts for bulk charging out of the 2800watt onan. I am supposing that could fully charge a 300AH LifePO4 bank in just three hours of generator time. But maybe that is pushing the Onan's limits. Any thoughts?

We have a 100 amp charger in our Roadtrek and it uses about 15 maps or so, maybe a bit more with inefficiencies. That is only half of the Onan output, so there won't be any issues unless you want to other things like run the AC or microwave or some other high load item. Many of the big chargers will limit their output if you have other things that need it more critically than charging. We never had a generator while the big charger was in place so never tried what you want to do, but I don't see an issue. I have ours turned down to 70 amps as it runs cooler and quieter there and when we do have shore power it is always for numerous hours. In retrospect, we could have gone much lower on the charging capacity and been just fine, both with alternators and shore power, as our use patterns and the 300 watts of solar do quite well, even with the compressor frig.
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Old 09-20-2021, 07:35 PM   #3
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We have a 100 amp charger in our Roadtrek and it uses about 15 maps or so, maybe a bit more with inefficiencies.
Thanks for your reply! I think this might a better solution for me then trying to upgrade the alternator because I do not drive much, and I do not mind running the onan for a few hours once or twice a week.

Which 100 amp charger do you use? Are you familiar with any commercially available higher amperage chargers?
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Old 09-20-2021, 07:41 PM   #4
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Thanks for your reply! I think this might a better solution for me then trying to upgrade the alternator because I do not drive much, and I do not mind running the onan for a few hours once or twice a week.

Which 100 amp charger do you use? Are you familiar with any commercially available higher amperage chargers?

We have a Magnum MS2000 inverter/charger. I think I have seen 120 amp chargers, but don't recall bigger than that, but you can parallel multiples of the same charger I would think without issue.
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Old 09-20-2021, 08:23 PM   #5
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you can parallel multiples of the same charger I would think without issue.
I wonder, then, if it could be as simple as just getting two more PD4645V 45 Amp 725 Watt converters (the upgrade for the old Magneteks), hooking them up in parallel to the battery bank, and then just wiring up a plug and plugging them in to the one of existing 15amp receptacles -- I don't have an inverter so I am supposing that the 120volt receptables are isolated from the 12volt system. That would give me potentially 135amps.
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Old 09-21-2021, 12:59 AM   #6
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Slow down. You don’t need that much charging capability. Install your lithium batteries and a battery monitor and use them with your standard converter. Don’t let it go over 14.4 volts (I use 14.3) and use it for a bit. Then decide how much more charging capability you need.
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Old 09-26-2021, 04:05 PM   #7
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Which 100 amp charger do you use? Are you familiar with any commercially available higher amperage chargers?
My 2005 Airstream motorhome came with the Xantrex Freedom 458 which is 140 amps, 3000 watt, 240 volt, but I have two 8D batteries it needs to charge, that's a lotta juice
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Old 09-26-2021, 04:59 PM   #8
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Not speaking from experience here , but I would be more concerned with the limits of the bms than the charger. You don't want to exceed the safe charging specs on your batteries.
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Old 09-26-2021, 08:59 PM   #9
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Just an FYI. Smart chargers are not additive so you can only have one.
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Old 09-26-2021, 10:23 PM   #10
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Just an FYI. Smart chargers are not additive so you can only have one.
I am thinking that any multi-stage charger that checks the batteries' voltage as it charges will run into problems with multiple chargers in parallel because each will read the voltage that the others are putting into the battery rather than the battery itself.

The PD chargers that I am thinking of using in parallel allow setting the charge level manually, so perhaps that would solve that problem. Just set each of the charges manually to bulk charge.
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