Hello,
My RMartin EVD VRLA will soon need new batts I suspect. I'd like to get Lifepo4s instead of VRLAs so that I can go more years without having to replace the batts again. But I'd like to do this as cheaply as possible. I'm assuming I won't need a new charger, controller, dc/dc converter, or motor if I get 12volt/50ah Lifepo4 battery packs? Hopefully that is true. I understand however that I would want a BMS for the Lifepo4s.
Now, in my fantasy world I would just swap out the 5 VRLA batts with 5 Lifepo4s having the same physical dimensions. Is that possible? Where could I purchase such batteries?
If that isn't possible, then any good prices out there on new BB EB50-12 batts? From my research they seem pricey. Best I could find was around $750 for 5 batts including shipping (from zbattery.com). The UB12500 batt is supposedly a cheaper replacement for the BB EB50-12. Are those any good?
Thanks in advance.
Yes its possible, and you would see better performance with the lower weight etc,
Try 5 of these
http://elitepowersolutions.com/products/product_info.php?cPath=25&products_id=90
Each is made from 4 x 40amphr Lifepos with integrated cell balancing, they will easily match a 50amphr SLA
you can use your existing charger, DC/DC converter, motor etc
I'd encourage you to go the LiFePO4 route. They entail a big up-front investment, but will far outlast and outperform Pb acid.
A BMS is needed - those individual cell-top voltage controllers sold by Elite Power Solutions and others are adequate, but you won't have a low-voltage cutoff. The whole-pack low-voltage cutoff most controllers have will be adequate if you are on a budget, as long as it cuts off at no lower than 2.5 v * #cells (i.e 50 volts) or 2.2 v per cell in cold weather (44 volts). Add an accurate voltmeter like an LCD self-powered panel gauge and don't let the pack go below 2.5 V per cell plus a safety margin when riding.
To replace 5 VLRA batteries you will need 20 LiFePO4 cells. They are called "3.3 volt" cells, but their nominal voltage under load is 3 volts. This is no different (but the reverse of) a "12-volt" battery really being 13.2 volts when it has no load. So, four lifePO4 cells exactly replaces one 12V Pb-acid battery. You can usually use the existing charger. A "40AH" LifePO4 battery pack is equivalent to a 70AH lead acid battery pack of the same voltage in actual capacity - i.e you range will be nearly doubled with the liFePO4's.
Finding a cell size that allows the cells to physically fit in the battery boxes is the biggest challenge. LiFePO4 cells are a lot lighter, but a bit bulkier than lead acid. Measure the battery box dimensions, look up the dimensions of some prospective cells, and do some calculating. The cells should preferably be mounted terminals-up, but mounting on their narrow sides will work too. You may have to raise the bottom of the seat helmet storage well or do other modifications. Barring this you may have to have new battery boxes made and welded into the frame.
The size of Elite battery don't fit to EVD battery box,only CHL fit it.
Thanks everyone for the helpful info. So I've learned from you guys that I can use a 40ah Lifepo4 to replace a 50ah sla. That's helpful since I had trouble finding 50ah Lifepo4s but there seem to be plenty of 40ah ones.
Now for the BMS. Where can I buy a BMS for 20 LifePo4 40ah cells?
If you buy a whole pack, the bms and charger are usually included. Try maybe ebay or Ping. You can buy 2 12v 20ah
packs and wire them parallel. I think your going to need a lifepo4 charger to fully charge a lifepo pack. SLA charger will only go up to 14v. you need slightly more than that to get bms cell balancing.
A 12v SLA charger can still work, however.
The simplest BMS is a distributed one, just using individual cell balancers that shunt if over their set voltage. They are only a few dollars each.
Also if u really did want 50ah lifepos, Im sure the nice chap from CHL would be delighted to sell u some - he posted above!
Because of the Peukert effect on lead-acid batteries, a 25-30Ah LiFePo4 would replace a 50Ah lead-acid....
Yes, correct !
Actually EVD 20hr lead acid 50AH is only 35-36AH capacity at 2 hours rate,plus its weight,the range is very short.
Our lithium 40AH is based on 1 hour rate,so that the 40AH capacity is big enough and price is reasonable.
We have 50AH Lithium battery too,but the cell is too high to be installed on EVD battery box.
We provide BMS and Charger too.
@CHL - What type of BHS do you recommend with your cells? Do you use the distributed type with a small circuit shunt across each cell? To me that looks like a neater solution than having many wires running to a central board?
Whats your companys view on this?
Thanks
We still use wiring BMS which is more stable and reliable.
PCM have self-discharged problem and it damage the cell if months no charging.
We will show you photos next week !
If you aren't afraid of a little soldering, there's a great BMS being sold in 'kit' form. The smart guys over at the Endless-Sphere forum have worked out an open source design, will sell you an empty printed circuit board, and give you the list of components to populate the board. It's a little bit of work, but highly educational, and keeps the cost low:
http://endless-sphere.com/forums/viewtopic.php?f=14&t=26554
A variation of this design is what's in my CuMoCo bike, and the newest release (4.4) is very well thought out. It'll give you excellent balancing and HVC, and also gives you a way to tie the LVC signal into your throttle. (You can't use full throttle once the batteries hit LVC, but might be able to limp home, which is about all you can ask for.)
My electric vehicle: CuMoCo C130 scooter.