Electric Bikes - charging/battery problem
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I have a 36volt 800watt hub motor bike (3 12 volt 12Ah lead acid batteries). It was a kit from ebay. I put it all together and it ran great for about a month. I could get about 15 miles or 45 to 60 minutes of run time before the batteries started to die. Now I can only get about 5 miles or 10 minutes of ride time before the batteries start to die (motor temporarily shuts off and "chatters" when coming on again under load). I took the batteries to an auto parts store after they had been acting weak- dead. They said each battery (12v 12Ah) tested at about 12.5 volts, and between 125 - 140 cold cranking amps. They said the batteries tested good and showed charged, but they won't run the bike at full power unless I charge them again for about 6 hours. Any suggestions???????
10-27-11, 01:21 AM
Maybe we got the same problem.
10-27-11, 10:01 PM
12.5v at rest means NOTHING...
You need to check voltage under load....
36v 800w is about 20+ amps from 12ah batteries with is almost 2C.
Lead acid batteries are rated at C / 20. You're pulling WAY to many amps from those batteries..
15 miles from 12AH batteries at 20amp loads is what prolly "killed 'em."
The cutoff is from the controller probably and is more than likely set at 32.4v (normal lifepo4 low voltage cutoff), which is 10.8v per 12v LA battery.. Even at 12.5v each, under load, they probably hit 10.8v each at 20a load.
My suggestion is either go easy on the throttle (go slower) and eventually buy Lifepo4 batteries.
10-28-11, 10:46 AM
What charger are you using?
SLA's will suffer greatly over long term if they are not being charged properly.
A lot of ebike kits do not come with chargers that are "intelligent" enough.
They must be disconnected from the pack once the charger flips to "ok" or "full".
If you don't the charger will still put a "trickle" charge on the pack and damage them.
Additionally, every cycle down to LVC, will cause a minute amount of sulfation on the SLA plates. Every cycle compounds this. Eventually the plates are so sulfated you barely get a charge out of the pack.
Use a FULLY automatic charger WITH a continuous de-sulfation/conditioner cycle. The conditioning cycle will work to "shock" the sulfate crystals on the lead plates and encourage them to go back into solution in the battery cells.
I use a Granite Digital Save-A-Battery 36V. My 7ah 12V cells are somewhere around 5-6 years old now and and the SAB has put a few extra miles back on them for my daily commute. I have been using mine for about two years now with zero loss of capacity. I plug my packs in every night all night and carry the charger with me to charge at work. (They are very light.) The also have polarity protection so you won't blow it up if you get your wiring backwards on the packs accidentally.
Save A Battery 2365-36 36-Volt Battery Charger and Maintainer via Amazon @ $85 or from their home page for $100.
There's a particular model of Soneil chargers that can do this as well. They cost about 50% more and I haven't tried those. "SR" models... I think.
Even the best charger /mainteiner is for nothing if you use crappy LeadAcid battery.
B&B is the best brand Lead batteries hands down.
I own Merida on lead 24V and I am tired of all this China-brands crap like HAZE which saged on the moderate short hill while B&B on the same exact hill keeps voltage and no LVC triggered on Merida.
I paid US$150 for two B&B 12V 12Ah batteries but I dont regret.
01-07-12, 12:16 AM
Here's my post I wrote a while back (copied and pasted):
"I had nothing but problems using SLA batteries for my ebike. After buying my 3rd pack of batteries(~$120/ each battery pack-3x 12V20A) within a year and a half. I thought to myself I could buy 3 more packs for the next year and a half (~$400) or get a LiFePO4 and have it last me for three years.
The problem I dislike the most is if you are not 100% on your charging/recharging cycles, you will notice a decrease in range through sulfuration. Each couple week, you'll notice another mile lost on range as sulfuration increases in your SLA pack. I went from 18miles on a single charge to ~ 6mile per charge, and it steadily got worst: 18, 17, 16, ....6 miles, then I would have to buy another pack. On the other hand LiFePO4 simply rocks, the range IINCREASED with each charge during the break in period, I could lock up my ebike for hours while not charging, and not worry if it lost range, awesome sense of freedom. It changed my ebike from a gimmick toy ( do I want to ride it today not knowing if I lost a mile in range from charging overnight?) to a workhorse that I can rely on...there are more benefits to LiFePO4 than what I mention, but I think you know them already.
SLA-High maintenace, very heavy, noticeable lost of range within months"
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