Cold Weather starting - Battery sizing?

[sideshow]

Hey - trying to plan out my build a bit, looking to see how much space this battery is going to take up.

Any tips on calculating battery size for cold weather starting? Probably get down to 45F/7C

I'm working with a 2cyl hatz - 2g40.

thanks!
Alex

[Eddy Wane]

Hi.
I wouldn't consider 45F/7C to be cold but the main consideration is to decide how much room you have to mount the battery. Then find out what the CCA (cold cranking amps) the engine needs, round that figure up to the next available size. Once you have that information you can then do a search to find a suitable battery. You may find that the Goldwing / BMW 1600 bikes may have a suitable battery that will do.
The other thing to note is how fast you can charge the battery for your next engine start.

[alexanderfoti]

Keep in mind that the battery ratings of these diesel engine manufacturers often is completely oversized.

I use a 12 ah battery (albeit a motobatt, excellent batteries) and it has a cca of about 450)

I have no issues using that, but I have a smaller engine.

[tappy]

The Hatz 2G40 has a 2KW+ starter motor. At 13V that's 150A. Given the voltage drop you'll get with a smallish battery I'd say 10V is a safer bet, so you need 200A.

An added issue is that the 2KW rating is at the motor's rated speed, and the motor's "stall torque" and corresponding current ratings will be much higher.
As such, you need a battery that can deliver still higher current, or need to prevent the motor from stalling. The latter is achieved by using a valve lifter to crack open the exhaust valves during cranking and so reduce starting compression. There's a fair bit of extra space in the top of the 2G40 rocker covers so it's something I'm going to be looking at myself.

These thoughts apply to the similar Ruggerini and Lombardini 850 anmd 950cc aircooled diesel twins.

As Alex says you need to check the Cold Cranking Amps rating of some batteries. AGM (absorbed glass matt) batteries are generally able to deliver a lot more grunt, consistently, than normal Lead Acid or Gel batteries.
County Battery Services list lots of batteries with their sizes and ratings and are very helpful & knowledgable, and pretty damn cheap too (if you're in the UK)!

A few AGM batteries they list are:
ETX15L-BS - 14Ah, 220A Cold Cranking, 134 x 90 x 166mm
ETX20L-BS - 18Ah, 310A Cold Cranking, 177 x 88 x 155mm
EXT16L-BS - 19Ah, 325A Cold Cranking, 175 x 100 x 155mm
EXT18L-BS - 20Ah, 340A Cold Cranking, 206 x 91 x 163mm

For comparison, a normal Lead-Acid YTX20 only delivers 250A Cold Cranking.
I'm planning on using an ETX20 at the moment - I think a 15 would be too small, but if I get round to making a valve lifter system I'll let you know how I get on.

[sideshow]

Thanks guys! Tappy - let me know if you do get into that! I'd like to hear how it goes.