View Single Post
Old 08-07-2010, 05:11 PM
Kevlarr's Avatar
Kevlarr Kevlarr is offline
Motorized Bicycle Elite Member
Join Date: Jul 2009
Location: Mi
Posts: 1,628
Default So long SLA and hello NiCads!

Well the 6v SLA I was using to run my lights bit the dust a couple of weeks ago, went for an evening ride and it wouldn't take a charge after. Thanks to a thread by 2Door I attributed the failure to having the battery mounted on it's side.

Ordered a new battery and it arrived Tuesday. Spent Wednesday making a nice metal battery box out of a sheet of scrap metal complete with a home built seat tube mount and fully padded to protect the battery. It looked slick as heck but after one ride without even using the lights (other then the brake light) I noticed the brake light wasn't working. I chalked it up to not fully charging the SLA with an overnight charge. Left the charger on all night and the next day it was showing 7.25v static bit as soon as I turned on my lights it dropped to 4.44v. UGH! NOT AGAIN!

This time I did some investigating. The lights were still only drawing .25A when everything was on and there wasn't any shorts or worn insulation in my wiring.
I have a diode in the white wire going into the battery for a half bridge rectifier, could it be my charging circuit? Did something short in my wiring box causing AC to go to the battery?
With the engine running I checked the positive lead coming from my wiring box to the battery with a DVM set on the AC setting and nothing so no AC going to the battery. I switched the DVM over to the DC setting and I think I found what was killing my battery. The mag is only putting out 2v off the white wire at idle and 4v at full rev! DAMMIT!
It was then I decided to give up on SLA batteries and check out NiCads. Checked out some local sources, Rat Shack wanted $6.99 a pair for 1300Mah C cells and the cheapest I could find was Harbor Freight at $3.99 a pair but that's still $12 in batteries to make a 7.2v pack. Then a light bulb went off, cheap cordless tool batteries are LOADED with sub C cells!
So I was off to the local Harbor Freight this morning to buy a 18v cordless battery they have on sale for $9.99 but unfortunately they were out of stock so I had to fork over $20 for another model of 18v battery. Still at $20 for a 18v pack works out to $1.33 per cell and with 15 batteries in a 18v pack I had enough to make two 7.2v packs so one's always charged.

If I wasn't so impatient and waited for the $9.99 packs to come in I would have only paid 66 a battery.

Last edited by Kevlarr; 08-07-2010 at 05:15 PM.
Reply With Quote