Trouble starting a Mitsubishi D1800

[UKcountrygirl]

Hi Tom.
Thanks for that advice. The existing battery is a 12v 40 Amp, and I've seen websites where 35 Amp is recommended but that seems too low to me, if the 40 is rattling around in the available space! She'll start with the 40, but you can tell that the battery is old, because it is not holding its charge through the winter months any more. People round here tend to have Massey's or John Deere's and don't seem to know a lot about Japanese mini-Tractors, so no-one to ask!
Thanks again.

 

[Ilikeurtractor]

Battery ratings can be quite confusing and here's a chance for me to add some more confusion Ideally a battery is rated for a certain energy rating (kW*hrs) at a certain temperature which would be in volt-amp-hours@temp or just amp-hours@temp since we are working with nominally rated batteries of 12VDC. Most generic batteries I've run across in the USA appear to list the "CCA" or cold cranking amps value. To me this doesn't mean a whole lot other than I can expect the battery to deliver the CCA value at some "cold" temperature that doesn't stand out as a listing on the battery.

I'm not sure what the 40 Amp rating refers to on your current battery. Most likely, the starter will draw anywhere from 100-200 Amps while cranking. Maybe it means the battery will put out 40 Amps for an hour at a minimum of 10 VDC or something.

Theoretically, if your glow plugs take 50 Amps (3 plugs) and you run them for 30 seconds and then operate the starter for 2 seconds (glow plugs going also during this) then you need a minimum battery capacity of roughly 50A*10V*30s+150A*10V*2s = 5kW*hr rating. I use 10V instead of 12V since battery voltage drops under loading. This is a much smaller energy rating than for batteries of the sizes we are used to on tractors. The problem gets into how much reserve capacity one should have if it doesn't start right up or is started multiple times before it is allowed to be recharged. Or even if you plan on using an electric winch which utimately will draw on battery reserves at times since most alternators won't have enough power available to drive them solely. Also how much capacity a battery retains over time decreases and plays into how long you expect it to be servicable.

That being said, the previous advice still holds though - get the biggest battery that will fit in the available space. High weight and available power are not limiting factors for a tractor, and generally the larger the battery the more power available for starting and more "reserve" capacity.

 

[TomSeller]

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I'm not sure what the 40 Amp rating refers to on your current battery. .

Probably 40 amp hour. Nice write up, very good.

 

[Ilikeurtractor]

Probably 40 amp hour. Nice write up, very good.

Thanks! Hope it can help out others. There are some really great technical articles out on the net on batteries and I'd recommend browsing around if one can spare the time. You'll be surprised what you'll find about them. I read one where a person can even reverse the polarity of a battery under certain charging conditions. Maybe not that useful but good to keep in the back of your mind in case you get some "crazy" readings on your meter.