The Fordson Tractor Pages Forum

One of my buddies called me this afternoon, he had put a new alternator on his farmall and when he started it the wires got hot and started to smoke. I went over to have a look, the wire is a 10ga and the alternator was rated for 85 amps, not a good combination. I’d have to guess the original generator put out 15 amps at best.

Pat

Did he put a positive charge 12 volt alt on a positive ground 6 volt tractor? Dandy Dave!

The previous owner had converted it to 12V with a alternator several years ago, I'm sure the unit he put on it had a much lower output, seems to me 40-45 amp was comon with the old GM alternators.

Pat

Yeah, I think you are right. 45 for a normal car and 60 Amp with AC and other power options. The wire may have been Hot in the past and has built up resistance. When he takes the wire out I bet he will find blue and burnt out spots in the copper. Dandy Dave!

I would suggest that either the [new] alternator is faulty or something else in the electrical system[s] has failed or is the cause of burnt out wiring.
If the previous alt. performed OK with the existing wiring, then the new one should also -- unless additional high amperage demand equipment was also fitted such as twin thermo. fans [which in some cases can draw 30 plus amps on start-up] or a home theatre system with boom box [!!??] Obviously, to cope with higher demand, the wiring should be up-rated. Even on low demand charging circuits I would always use a minimum of 50amp. rated wire. If nothing else it lessens voltage drop losses. For higher demand the wiring could be 'twinned'.
Any modern alternator is internally regulated to provide ONLY the amperage demanded of it and it matters not if it's rated output is capable of 30amps. or 130. The voltage of a rated 12volt unit is fixed to a general voltage maximum of 14volts to cope with low or flat batteries. If this was 'crook' and over-charging because of a faulty diode pack, then either the alternator would burn out and/or the battery would start to fume [very dangerous!]
If it is believed that the new alternator is 'good', then I would, first off, check the existing wiring circuit -- especially for a short. Secondly I would use a volt meter across the battery terminals; and if found OK then use a rated clamp-on ammeter around the alt. output wire.
Of course, it could be a bit difficult, as a last resource, trundling a tractor down the road to an auto electrician. The next best thing is to take the unit to them.
Pavel

Totaly Agree with you Pavel. If the previous Alt shorted out causing the wire to heat up because the Alt grounded internally, the the copper wire will break down and become resistant much like Nichrome wire and heat up. I've seen it before. I second Replacing the wire and have the Alt checked. Dandy Dave!

I did omit to mention one thing -- even though it's fairly obvious.
If the replacement alternator is an un-regulated type [has a separate regulator] and is fitted replacing a former internally regulated one, then the amperage output of the now fitted one will be at a continuous maximum of, in this case, 85amps. Burnt out wires would be the least of your worries!
Pavel