How much Voltage drop is acceptable?

[dmac]

Hi,
Just in the middle of troubleshooting some electrical Gremlins and have notice i have -.48 voltage drop between my positive batteries and the positive on the Alternator when i have the ute doing 1500rpm and every electrical component on, eg lights, fan, heater, aircon, highbeam. To me that seams a bit high but im not sure for a diesel.
Have traced the resistance to be at the loom plug just next to the passenger side battery.
Pre loom its -.03 voltd and then post loom to alternator its -.48 voktt.
Ive pulled the plug apart, cleaned it to the best of my ability but not much change.
Is this normal?

 

[Old.Tony]

A voltage drop across a plug indicates something wrong with the plug. I don't know if you can get the pins out of the plug and check the bonding of the wires to the plug. This sort of drop would indicate either dirt in the plug (you've discounted that) or some of the wires have disengaged from the crimp holding them in.

 

[Horatius]

Hi,
Just in the middle of troubleshooting some electrical Gremlins and have notice i have -.48 voltage drop between my positive batteries and the positive on the Alternator when i have the ute doing 1500rpm and every electrical component on, eg lights, fan, heater, aircon, highbeam. To me that seams a bit high but im not sure for a diesel.
Have traced the resistance to be at the loom plug just next to the passenger side battery.
Pre loom its -.03 voltd and then post loom to alternator its -.48 voktt.
Ive pulled the plug apart, cleaned it to the best of my ability but not much change.
Is this normal?

Shouldn't make any difference the type of motor, it's still an alternator/battery circuit. What "gremlins" were you having?

What voltage do yo have across the battery at 1500 rpm? I get 14.3V though with everything on (fridge, stereo, fan, high beam/driving lights) it can drop to 13.9V. Have always assumed it would be much the same at the alternator itself, but don't know that for sure. If I get a chance I'll measure it.

Obviously you've checked all the connections, battery terminals, chassis earth and so on?

 

[Horatius]

ps. when you say you've "traced the resistance" to a plug does that mean you have measured a voltage drop across it, or measured the resistance through it? If it is at a plug it will eventually get worse and become a "hot joint" and one day burn out. If that is the problem maybe you could get a through join/crimp link and do away with the plug?

pps. I notice from another thread your alternator reaches 18V intermittently and you have 1.5V drop on your earth (assuming you get 1.5V from negative battery terminal to chassis?). If so there's a crook connection there somewhere. If you can fix that and it still happens it sounds like the regulator/alternator might be on the way also. Afaik apart from a regulator there is also a rectifier and if there is a problem (with the diodes for instance) you could get all weird sorts of problems from alternating currents/ voltages?