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Dual alternator effects tach?

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dual alt tach
906 views 7 replies 5 participants last post by  JMJNet 
#1 ·
I just put a second alternator on my truck and works great . I used the brown wire to energize it .I should not I used a alternator off a obd1 style truck. First I tapped the brown wire to the existing brown wire off the original wire and I thought all was good .had fantastic volts at idle volt meter reads one line past the 14. But here's where it went screwy .my tach drops dead at idle but comes back at 15oo rpm . I than figured it was the tach wire that had to be energized so I hooked it up different. Being I replaced my AC compressor with this alternator I than jumped a few wires so I can now turn on or off the second alternator from inside the truck using the a/c button . Same thing ! Tach don't work at idle with it on . Turn it off ,works fine . Turn it on turn on lights (I have 6 extra ) turn blower motor on voltage drops a tiny bit boom tach works. Rev it up tach stops working till a 1ooo rpm than come back at 15oo. ... could the higher voltage be screwing with it ? It's k excessive high but it's a constant 14.5volts Engine Vehicle Auto part Car Automotive engine part


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#2 ·
Best way of describing what is happening is post 6 of this thread (hopefully it work right)

http://www.thetruckstop.us/forum/index.php?threads/33587/


Simple thing is to run a separate sense wire that ends at a location separate from the first tachometer...or more complicated get a different alternator pulley and pull tach from the one with the smallest pulley.


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#3 ·
Do you have some sort of isolating / combining device in the system? Double check that you have it connected correctly. I sounds like they are not isolated properly and are intermittently fighting each other and or only one is running sometimes.
 
#5 ·
K so I narrowed it down to this . There not so much fighting each other but I guess the new one is being the dominant one once the voltage gets to 14.5 the voltage regulator in the factory one shuts it's self down from over powering everything . But being this is my winter truck I always drive at night or have the heater on and that draws enough to wake the original alternator up and my tach comes back. I have now wired it up to be able to control it with my AC switch inside the truck . I just wish it didn't automatically come on when the heater is turned to defrost .

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#4 ·
Oh and there is a threaded connector behind the grille that you can unscrew to remove the AC hose assembly since it doesn't look like you will be using it any time soon. Might as well pull the condenser to improve the flow through the radiator at some point too.
 
#6 ·
You could try hooking the S wires up to the same point. That way if they are both set to 14.5 they should be making and reading at the same point like fuse box input.

Now they are each reading at their own output terminals so even if they are both accurately and theoretically going for the same voltage the differences in the loads and wiring could be making one do more.

My personal opinion 2 alternators running one system doesn't make sense. Makes a lot of sense if they are running separate systems like your typical separate starting and house systems.
 
#8 ·
There are a lot of al option which give you higher amp-acity so you won't need 2 alts.
AD244 alt already have 130 amps stock, there are version up to 220 amps.
 
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