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Old 07-14-2015, 09:52 PM   #11
Peter Tourin
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Default Re: Replacing OEM batteries with LiFePO4's

Don, I called Best Converter but didn't get Randy. I'm thinking of that 9100L line of chargers - the PD9160AL, PD9170AL or PD9180AL. They were a bit confusing - the man I talked to said that although they list the converters, they don't actually sell them there - he referred me somewhere else.

Smiller, that's also what I understand - that the charger is a fixed voltage supply that puts out 14.4 - 14.6 volts. All the Progressive Dynamics lith chargers default to 14.6 I don't yet fully understand how the BMS works. It sounds like when you're driving or connected to shore power, the BMS relay opens at full charge - then the batteries are out of the circuit and house 12 vdc is provided by the converter/charger. When you're not driving and not connected to shore power, the BMS relay is closed and you start drawing battery power. If you look at the battery curve, the voltage drop is so low that when the relay opens on 8V low voltage, you're down at very near what we'd call full discharge - around 95% depth of discharge. I'm not saying this is a good idea in daily use! But the battery manufacturers are saying that if you drag the batteries down that far, the BMS will open the relay to protect the battery from damage. And they're saying that going down to 80 or 90% DOD won't damage the battery chemistry as is the case with flooded cells. That extra usable capacity is one of the things that makes the lith batteries interesting.
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Old 07-14-2015, 10:08 PM   #12
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Old 07-14-2015, 11:20 PM   #13
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Default Re: Replacing OEM batteries with LiFePO4's

BTW - if I understand this correctly, it means that whether the batteries are being charged at 14.6v or the BMS disconnects them, the house is being run on 14.6v since the converter/charger is holding the house there. I assume that 12v equipment can operate on 14.6 with no ill effects, though I never thought about it before now. I hope that's the case...

And now I'm back to the original post - thinking about which charger. If the A/C uses 12.5A (and probably more when it starts up) and one of the Progressive Dynamics chargers uses 10.5 or 10.9A depending on the size, it appears that I'm still fine to run the A/C while the charger is at work. They'd take some wiring changes, and the 80A charger would require a BD2015 breaker to replace the existing BD1515 as that charger requires a 20A circuit, but I wouldn't be overloading the 30A service - unless I then use the microwave, a hair dryer or coffee maker <g>... It would just be a matter of paying proper attention, and you already have to do that in an RV.
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Old 07-15-2015, 12:22 AM   #14
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Default Re: Replacing OEM batteries with LiFePO4's

Popping a fuse or two to find out your limits is not a bad thing.
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Old 07-15-2015, 12:42 AM   #15
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Default Re: Replacing OEM batteries with LiFePO4's

Certainly better than melted wiring <g>...
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Old 07-15-2015, 01:44 AM   #16
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Default Re: Replacing OEM batteries with LiFePO4's

When I mentioned to the BMS (battery management system) above I was referring to the module built into the SmartBattery that controls the charging regiment and protects against overcharge and undervoltage. The specs on their website specify 14.4 to 14.6 volts charging supply (at up to 100 amps charge current) so I would assume that any reasonable-quality regulated supply will suffice, in fact your Parallax may work -- it's single fixed voltage is a poor performer when charging lead-acid batteries but with the BMS resident in the battery doing the 'smart stuff' then a fixed voltage supply is OK, so you can adjust your Parallax to the proper voltage and I expect it would work fine. Something like a Progressive Dynamics or Iota would probably be better for severe duty but if all you need is a fixed voltage supply the the Parallax would probably work, although I'd agree that if you are going to invest in Lithium batteries then you might as well get something capable of a higher charge current.

14.6 volts shouldn't hurt anything on the DC buss, in fact any decent lead-acid charger is going to sit around that voltage while charging. Your vehicular electrical system runs at around 14.1 volts and I guess you'd have to ask Smartbattery whether that is adequate for charging while underway.
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Old 07-15-2015, 02:18 AM   #17
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Default Re: Replacing OEM batteries with LiFePO4's

Yep, that's how I understand it. SmartBattery happens to put the BMS inside. AM Solar's batteries have it external, as do several of the cell suppliers I've looked into. But I assume the basic BMS design intentions are similar.

I don't know if the Parallax charger voltage is adjustable - I can't find any technical info on it at all. It would be handy, at least for a start, if I could simply jack the voltage up and start driving <g>...

I've been assuming that the SmartBattery internal BMS has to sense an over-voltage in order to open, and I've assumed that this situation would be when the voltage rises to somewhere in the vicinity of 14.4 volts - if it's higher than that, the battery would let the charger remain connected and charging, which I don't think they want. I also assume that if I connected the Parallax charger as it stands (putting out 13.6 volts or so), that it would also stay on forever without the relay opening. But I don't know this - I don't understand the dynamic charging characteristics of standard and AGM batteries, much less these. I wish there were more technical articles around.
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Old 07-15-2015, 02:33 AM   #18
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Default Re: Replacing OEM batteries with LiFePO4's

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I don't know if the Parallax charger voltage is adjustable - I can't find any technical info on it at all. It would be handy, at least for a start, if I could simply jack the voltage up and start driving <g>...
It's not officially adjustable but it's pretty easy to do. If you remove the charging section (located below the circuit breaker/fuse section) there will be a pot at the rear of the circuit board, adjust that to the desired voltage and you're good to go.
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Old 07-15-2015, 03:58 AM   #19
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Default Re: Replacing OEM batteries with LiFePO4's

You mean slide it out so you can get to the pot, but don't disconnect it - run it and turn the pot while measuring the voltage? I wonder how high it can be set? That'd be worth doing, as I'm still not sure just what to replace it with. The PD 9100L series are 9" deep - they stick out the back and I'd have to relocate some wiring and an LP furnace duct. Also, it's not a hard-wired unit (it has a plug), so I'd have to wire in an electrical box for a receptacle. All manageable, but I keep wondering if I just haven't found a charger yet that'll work a bit easier...
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Old 07-15-2015, 04:49 AM   #20
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Default Re: Replacing OEM batteries with LiFePO4's

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You mean slide it out so you can get to the pot, but don't disconnect it - run it and turn the pot while measuring the voltage? I wonder how high it can be set? That'd be worth doing, as I'm still not sure just what to replace it with. The PD 9100L series are 9" deep - they stick out the back and I'd have to relocate some wiring and an LP furnace duct. Also, it's not a hard-wired unit (it has a plug), so I'd have to wire in an electrical box for a receptacle. All manageable, but I keep wondering if I just haven't found a charger yet that'll work a bit easier...
My replacement converter charger was also set up for a plug; I just cut it off and hard wired it. No big deal.
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