Topic: Small Battery (amps not dimensions)

[75modrat]

I know others have asked about how small of a battery they can use. Unfortunately people gave dimensions or questioned why someone would want to do it. I am running a 1975 cb750K. The bike is going to be rewired removing all the things that are not a necessity (no turn signals, etc). Also, I plan to add a switch so I can keep the headlight/taillight from drawing power when starting. I need to know what the minimum amount of amps I am going to need. I have a round oil tank with a battery box in it. I want to put a battery and the electronics in the box to clean it all up. Any insight would be greatly appreciated.

Frank

[dusterdude]

if you`re not using the electric starter,you can probably get by with a 6 amp or so battery.i seem to remember the oe battery for my panhead was a 6 amp or thereabout.

[TwoTired]

The stock 5 ohm coils, take about 2.4 amps.  The alternator draws about 2 amps.  Different coils may draw more current.
The above is constant draw whether the engine is spinning or not, about 55-60 Watts, which is right about what you expect from the alternator at idle. 
Electric start takes about 120 amps.  If you still wish to electric start, I suggest you abandon your small battery desires.

That speaks toward capability.  The next concern is duration or capacity.  As batteries deplete, their voltage falls, as does voltage under heavy loading.  If your bike starts quickly, 5-10 seconds is all you need.  Batteries are rated in amp hours (AH), or how many amps it can provide in one hour and still have enough voltage to supply spark voltage.  You will likely be best served with a battery rated 5 AH or better.  And, if you aren't ever far from a shop battery charger, a 2.5 AH battery would run the two essentials for 20 minutes and still have enough to pop the spark plug... when the battery is new.  However, such high loading and deep discharge cycles will shorten battery life, and require frequent replacement.  But, for racing applications, that probably won't be much concern.

Cheers,

[754]

12 N 5.5A-3B..........approx 5x4.5x4.5

is pretty standard for cutom bikes, easy to get at any custom bike shop or H-D shop on the road.

Fits in 750 tray but usually run wood block under it so cables are easier to mount.. and make sure it cannot move around.

If its a custom tank, it is either setup for that or a small rectangular.

[johnny_from_bel]

Yep 6AH should do the trick if you dump de electric starter.

[dusterdude]

damn 754,you`re pretty good for a canuck.

[Buber]

There is a neat trick - BUT you CAN"T use the electric starter. Trick is to look for batteries from UPS (not the shipping company, but uninterrupted power supply units for computers  ). They come in many shapes & sizes & amps, cost a little, and the best - they are gel batteries, totally maintenance free, and you can even mount them on the side and so on. You may need to do a connector conversion, as connectors are obvoiusly different, but if you are not gonna use the starter, then this is the BEST choice. And they are easily available.