battery charging

Discussion in 'General Electronics Chat' started by djbrooksy, Apr 25, 2010.

1. djbrooksy Thread Starter New Member

Sep 19, 2009
4
0
HI guys and girls

this is going to be a stupid question i know ya all love them

ok i have a pit bike or a minni bike whatever you wish to
call them.
i have a EFI kit to go on http://www.mbe-motorsports.com/catalog/product_info.php/cPath/22/products_id/188

now my problem is i dont wish to run a full size battery that you would
find on these bike as it will only be needed to power up the ecu before
i start the bike.
the battery i wish to use is a 12v 1.2amp VRLA as its small and light
but dont wish to cook the thing with charging circuit from the bike.
The bikes output is 12 to 14 volts at 4 to 6 amps
do i need to panic about cooking the battery
any help guys would be great

cheers mick

PS sorry about spelling and gramma its not one of my strong points

2. rjenkins AAC Fanatic!

Nov 6, 2005
1,015
69
I'd think something like a small power diode and a low value resistor in parallel.

Connect that in series with the battery.

The resistor will limit the maximum chanrge current to the battery, and the diode will bypass that if a heavy current is drawn to prevent excess voltage drop.

The resistor value should be high enough to limit the charge current to whatever the battery can handle, assuming the charge system is regulated to about 15V.

eg. if the battery can take half an amp and it's nominal voltage is 12v, dropping 3V at 0.5A needs 6 ohms. Try a 5.6 or 6.8 Ohm resistor.

3. djbrooksy Thread Starter New Member

Sep 19, 2009
4
0
thanks for the quick reply just so im geting what your laying down
something like this
so the resistor keeps current down but the diode will let the ecu have full power when needed

the max charge current is 0.24A at 13.8 volts
thats a float charge anyway but it will only ever need to be topped back up

4. retched AAC Fanatic!

Dec 5, 2009
5,200
316
From the charger to the battery.

That way, the power coming from the charger to the battery passes through the resistor, limiting the charging current. But If the ECU (or anything else) needs more current FROM the battery, the diode will allow it to bypass the resistor.

5. djbrooksy Thread Starter New Member

Sep 19, 2009
4
0
ok so now i have that under control
working with the calculator here
http://www.the12volt.com/ohm/page2.asp

the DC output after the reg/rec on the bike