On Tuesday, 17 April 2018 12:05:45 UTC+1, Graeme wrote:
In message ,
tabbypurr writes
On Tuesday, 17 April 2018 10:55:42 UTC+1, Graeme wrote:


Back to the Morris. I have an ammeter, 30-0-30, and the dynamo is rated
13.5v, 22 amps. Still +ve earth. What I don't have is suitable brown
cable, and there seems to be a lot of conflicting advice.

was the original brown?

There isn't an original as such, but yes, the cable being extended is
brown, so I would like to follow the same scheme.

Found cable described as 3.0mm² 44/0.30 27.5 Amp, which seems OK, or
should I go for 4.5mm² 65/0.30 35 Amp to be on the safe side?

Voltage drop is likely to be the no 1 consideration. 1mm2 pair drops
44mV per amp per metre, so 22A 3mm2 drops 0.323 volts per metre. 1m of
that is going to seriously hamper your battery charging.

OK, good point. I will go for the larger size. It is certainly a
common addition to a Minor, even (or particularly) those still using a
dynamo.

Any idea of 'standard' car Lucar connector size? Options seem to be
6.3mm, 8mm etc. I'm guessing 6.3, being equivalent to the old 1/4 inch?

you're the one with the measurand!

grin Well, yes, but measuring to a fraction of a mm with a steel rule
is not easy, particularly when the connection is buried under the
bonnet. I'm sure 1/4 inch was the 'standard' automotive size back in
the day, and 6.3mm is close enough to 1/4 inch.

4.5mm2 will get you 0.215v drop at full current, not as bad but still hampers charging on an already low voltage output.

A battery voltmeter is a way to avoid the issue, preferably expanded scale from 10v to 15v, or in your case 14v.


NT