42AH AGM range extender battery to A123 AMP20 20AH?

[arkmundi]

Opinions?
I'm looking for the most cost effective range-extender. What I'm thinking about is the Concorde Sun Xtender PVX-420T, 12V, 42AH AGM Battery through the Alt-E Store. Three of them in series and then connected in parallel to my A123 AMP20 12S 36V main pack. I theorize that the LiFePO4 high-C pack would always be the draw, so power would tend to flow from the lower-C AGM into the main pack. Its all 36V, just wired together and without any charge controller. Would this work The Concorde batteries are deep-cycle, engineered for solar power, coming in at $155.49 apiece. So its $466.47 for a 3S 36V configuration, yielding an additional ~42 amp-hours. I'm hoping to travel 50-60 miles on a single charge, the extra 90 lbs of battery in my cargo trailer. Suggestions for better battery tech?. Thanks.

 

[arkmundi]

Look, I have some events coming up, like the "march from coal to Cape Wind", a 1000+ march from Brayton Point's largest coal fired plant in New England, to the site of Cape Wind, the largest offshore wind farm in American waters. Having had polio and having walking difficult, I use my ebike as much as a wheel chair as for transportation. So the range extender is my gambit to participate. I'm trying my best to tap the expertise here and hope that there is some, as I try to build a 36V 6o+AH battery that has a mix of LiFePO4 and Lead-AGM. Anyone have experience with this or am I on the bleeding edge?

 

[dogman dan]

It will work. the AGM may charge to a lower voltage, so you might want to bleed off 2v from the lifepo4 before you hook them up, if the lifepo4 just got charged. Depends on your lifepo4 charger, if it goes to 60v, that might be a bit high for the lead. 58v should be ok.

But here's the deal, It's not worth it, if you can get 20 ah more lithium for a similar price. Why? Because you had better not discharge the lead as deep as you could lithium, AND it's gonna weigh a ton. That weight will cost you some range. So you will haul a lot of weight, for perhaps 20-25 ah of usable ah.

So you will be better off to just get more lifepo4, but it doesn't have to be A123. It can be an inexpensive sun thing pack or whatever. Get 20 ah if you can, and if not, settle for 15 ah. 35 ah of lithium should get you 60 miles at sub 20 mph speeds. If you can get another 36v 20 ah lifepo4, you will have up to 80 miles of range, and 60 miles at 20-22 mph. 50 mile range at 25 mph. This is not calculation, it's what I've done in the real world on two pingbatteries.

 

[arkmundi]

Yea, I almost did buy more A123 AMP20 battery capacity. I had the idea of four 6S, in paniers. so it'd ultimately be a 12S3P 36V 60AH pack. But... and its a kicker, I'd not do that without also buying a BMS (I currently run without one). And then... the extra cells, as my experience with cell failure is 4 dead out of 20 purchased. That's a 20% failure rate, so I'd need 32 additional cells. But, as you say, it can be lipo. What's your opinion on the current best bang for the buck battery out there?

 

[LeftieBiker]

I've had no problems with lead-silicone batteries in my scooters. No dead cells, no BMS to malfunction, just extra weight and lower capacity, with 100% reliabilty. The supposed biggest advantage to these batteries is they won't sulphate up when sitting around not fully charged, because there is no sulphur in them. You shouldn't discharge them more than 80% at most, but it seems now that this applies to lithium packs as well...

 

[dogman dan]

I was just suggesting a lower c rate version of lifepo4. Then you have perfectly matching cell voltages. Since you would parallel it with your A123's, you would not have to get expensive high c rate stuff. The A123 will pull the amps when you need it for a hill or whatever. Your range extending pack can then just be something able to do 1c or so. You shouldn't need 60 ah total to do what you want, unless you want to haul ass all the way. At no more than 20 mph, 40 ah will take you 60 miles. If you plan on riding fast, the lead gets to be a worse and worse idea.

I you don't have a ton of money right now, you could buy a 36v 10 ah now to go in one pannier, then add another 36v 10 ah later to go in the other pannier. If you don't want a bms, the seller should be willing to sell you the thing a bit cheaper.

Lipo is an option, but it gets slightly awkward paralleling RC lipo with lifepo4 because of differing voltages of the cells. 16s lifepo4 matches 14s lipo reasonably well, but 10s lipo doesn't match 12 lifepo4 as good.

However, you could easily run a lipo pack by itself since it has high c rates. So you could run your A123 for awhile, then switch to a lipo pack. 10s, (36v) 20 ah will cost you around $350-400, but since you will have a new chemistry you'd have to buy new charging system for it. Just buy lifepo4, and you already have the charger for 12s lifepo4.

I just think your best bet will be to find some affordable lower c rate lifepo4. It could be an ebay duct tape pack, a pingbattery, or some 20 ah prismatic cells.

On the other hand, if you were getting the lead free somewhere, such as somebody replacing emergency lighting batteries, it would be a different story. It would be worth it to carry the lead if it was free.

 

[999zip999]

lead is dead.Get lifepo.