Tach

[funnnyfarm]

I am working on a 1996 75 hp Force, the tach quit working. I tested the regulator rectifier, red wire has 12 vdc, gray wire from regulator to tach - good. When I checked the two yellow wires to ground no continuity there. But when I ohm yellow wire to yellow wire I get nothing. And the check of the diodes in the regulator I got continuity both ways, bad diode, so the stator is bad and so is the regulator. I am wandering if the 3 deep cycle battery’s were very low, and pulled to much for the stator and regulator and that’s why they went bad? Thanks funnnyfarm

 

[Chris1956]

I do not believe batteries can pull enough power to damage the diodes. The diodes restrict current. Most every AC battery charger has diodes and people use them to charge bad batteries all the time.


However, disconnecting the battery from the diodes will definitely damage them.

 

[funnnyfarm]

Thanks Chris1956. Have a great day.

 

[sam am I]

So yes, sort of, but depends....Think "Forward Current", "iF", forward biased NOT reverse!

https://circuitglobe.com/wp-content/uploads/2015/12/maximum-forward-current.jpg

If the diodes forward current ("iF")rating was/is greater than of the max current that the stator could produce, then no!

In theory(snickering), you could literally short circuit the DC output of the rectifiers and because the max current that can be produced by the source(stator in our case/example) is capped/crapping out at that certain max value, the stator's inability to exceed the diodes forward current spec'd rating keeps the diodes safe no matter the load(eg, BIG dead battey's). The diodes would just get mostly hot.....Not good practice but again, "in theory" they'd be okay.

HOWEVER, if the forward current ("iF") rating is LOWER than the stator's max output, then POOF!! With a load that would draw more current than the diodes could handle, the diodes would smoke easily because the stator can produce a greater current than the diodes can handle going through them.

So, hope that helps and I reckon it is a design depend answer mostly, that is, unless someone has modified and/or replaced with less than spec'd values and/or.......Chinese/off market parts sometime can get ya in trouble.