battery charging

jdcburg · #1 (**permalink**) 07-26-2009, 03:51 PM

I've been reading this forum recently in preparation for starting my own ebike build, which I intend to power with a 24 volt 350 watt motor. I will be buying a pair of 12 volt 12 ah SLAs to hook in series to make 24 volts. I have a 12 volt charger, so my question is: can I switch the jumper wire(s) to make them parallel and charge them with the 12 volt charger, or should I unhook them and charge them separately, or just break down and buy a 24 volt charger ($17 on eBay)?

I have a pair of old Huffy 3-speed bikes. They have the internal gears in the rear axle. I have put the rear wheel from one on the front of the other and will be mounting a geared down motor from a Razor Dirt Quad over that wheel. A total drive ratio of 14:1 on the 26 inch wheel should give me about 16 mph and enough power for the hills around here, plus it should freewheel easily when I am pedaling with the motor off. That's the hypothesis anyway. I'll keep you posted as the project progresses...

Cabinfever1977 · #2 (**permalink**) 07-26-2009, 04:06 PM

buy the 24volt charger.

deacon · #3 (**permalink**) 07-27-2009, 08:30 PM

I use two battery tenders from walmart and charge the batteries separately but at the same time. It seems to do a pretty good job so far.

jdcburg · #4 (**permalink**) 07-29-2009, 06:08 PM

Thank you for your responses. I will keep you posted - jd

zendiecut · #5 (**permalink**) 07-29-2009, 06:18 PM

you could use a switch to separate the batteries into 12v units for charging and then throw the switch in the other position and they will be connected into 24 volt unit.
You need to know th efloat voltage of the battery packs. That is the charged voltage, not the running voltage. Your car generator (really a rectified, regulated alternator) outputs about 14 volts to charge the 12 volt battery.
I built a bike light using 4 6 volt celss I bought from All-Battery.com - Rechargeable batteries & Chargers. It's a 12 volt light 2 6's in series making a 12 v unit x 2 off those. I used an old Ryobi 14.4 volt battery pack as my interface between the charger and batteries. I needed the 14.4 because the float voltage of the 6 v cells is 7.2 volts. The manufacturer should have that info for you. If you have an old drill set up with dead batteries, I can send you details on how to do it.

Jack

DOC BOLM · #6 (**permalink**) 07-29-2009, 06:25 PM

I bought 6 guest chargers on ebay.220454053591.make offer of 20.00.These are 3 stage 24v 3a chargers.I have 6 batterys for my 3 bikes.After a ride it takes less than 1 hour to charge each one.Harleys Dad

deacon · #7 (**permalink**) 07-30-2009, 06:55 AM

Doc I like the time of your charger. Mine takes at least three hours at 1.5 volts. Someday I might upgrade to a faster charger. Right now I am still waiting for the huge breakthrough on the price of the Liths.

jdcburg · #8 (**permalink**) 08-18-2009, 07:08 PM

Just a quick note to let you know I have only had time for 3 short test runs. The longest was about 5 miles out and back, up and down 2 pretty good hills in each direction. Total time - about 40 minutes, probably 25-30 minutes under power with pedal assist. The highest point (also the furthest point) was probably 175-200 vertical feet above the start. I didn't notice any drop in power at the end of the ride. I decided to try hooking the batteries in parallel and charging them with the 12 v charger. It has an ammeter and after that ride it charged at 5 amps for about an hour and then it dropped back to 2 amps. I left it for another hour and turned it off. I haven't had a chance to run the batteries to a noticeable drop in power, but maybe this weekend. I'm going to start carrying a notebook and writing the variables down so I can be a little more scientific with my analysis. Also, I only have an analog multimeter at this point, but I may spring for a digital, so I can get more accurate voltage readings - jd