Voltage query
 

XT600E, 1995, battery 3 months old. Bike not touched for 10 days, battery voltage 12.8V. At a fast idle, voltage 13.7V.

This says to me that the battery is healthy enough, but I would have expected a higher reading at fast idle. Does this mean the alternator is letting the side down? What might be wrong? Any ideas?

I would expect about 14.5V at fast idle.
Are you sure your voltmeter is accurate???

It won't affect things too much but I'd keep an eye on it.

Actual real life readings from bikes will vary but the theory says that 13.7v is 0.5 volts over the maximum the battery can hold and I'd say was an acceptable charging voltage. Your battery will have 6 cells and each cell will be 2.2v fully charged, 6 x 2.2v = 13.2v. The standing voltage of 12.8v is quite good. I shouldn't worry, most peoples bikes will probably be worse than yours!

Thanks for the replies, guys. I always understood that a healthy alt should be delivering about 14.4V at fast idle, and I reckoned that 13.7 was a bit low. The bike starts fairly well, so that isn't a huge drain, but my commute is in the dark both ways at this time of year, so the charging system is getting a bit of a caning. I don't fancy getting stuck on a dark lane in this kind of weather!

The voltmeter is a digital one, so I assume it's accurate. At least, it reads zero when it should, and showed my other bike churning out 14.4V, so it's not far out.

I'll keep an eye on the charging system, however, and if voltage deteriorates further I will look into it.

Cheers.

I thinks it fine, the reason for it to only charge 13 something could be that your battery is fully charged, or you dont rev it enough.

I think the max charging current is around 4500rpm +/- 500 rpm.

No worries, tho.

Thanks, Jens.

Don't get me started on the difference between voltage and current!

Remember that you are measuring the output of the voltage regulator and not the alternator. The alternator is most likely 3 phase AC and this voltage will rise with the revs. However, the voltage regulator rectifies this to a DC signal and limits (regulates) the maximum voltage. This is why your battery cooks when your regulator fails as a high AC voltage is applied to the cells, they don't like that much!

Having said all that you really only need to know that with your headlight on and heated grips etc that the battery is being charged at above 13vdc. Then everything should be honky dory.

That's very helpful, thanks. I am aware of the function of the reg/rec - in referring to the alt output I was trying to keep it simple. You are quite right - a charging voltage outside certain limits is probably the reg/rec at fault rather than a duff alternator. My question to the forum was really to post the results and see if they were in line with what other owners have experienced.

So - everything electrical switched on, output >13V, all well? Great, and thanks. (I don't have heated grips yet, but given the temperatures round here lately, I think I might.)

That voltage reading is fine. Its a very acceptable read after being stood for the 10 days and there is nothing at all wrong with the charge rate either.

Thanks for the confirmation. All's well with the XT then, electrically speaking. Now there's just the duff battery on the Pan Euro to sort out :)