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Old 28-06-2014, 23:45   #1
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Solar panels disabling tach

When the sun is out and I am using the engine, the higher voltage from the solar panels disables the tachometer. When this happens, does this also stop the alternator from charging the batteries?
Thanks, Mike
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Old 29-06-2014, 08:47   #2
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Re: Solar panels disabling tach

It's hard to tell you without seeing a diagram of your electrical system, but there's different kinds of tachs, and yours probably works off the output of the alternator either directly or coming off a controller, and the extra power from the solar is causing it to malfunction.

They make tach sensors that are optical or magnetic that count the teeth of the flywheel as they go by, that would resolve your issue.

Your alternator is probably functioning normally while the tach's not working, but the best way to tell would be to check your battery monitor or get out the multimeter.
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Old 29-06-2014, 09:29   #3
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Re: Solar panels disabling tach

Quote:
Originally Posted by mrybas View Post
When the sun is out and I am using the engine, the higher voltage from the solar panels disables the tachometer. When this happens, does this also stop the alternator from charging the batteries?
Thanks, Mike
SV Hartley
Currently Huahine, French Polynesia
Yes it does and it generally means the bank is full anyway and the alt is not really needed. If the tach goes on and off and on and off it means it is still needed and the solar controller, in conjunction with the alt, drives over alt reg limit. When the solar can no longer support that voltage set point the system voltage drops and the alt kicks back in.

#1 Install a switch to turn off your solar. Every controller manufacturer has their own recommendations for this. Genasun for example wants controller B+ to the battery cut.. Morningstar recommends a double pole relay to cut + panel feed and + battery feed simultaneously.

#2 Adjust the absorption & float voltages 0.1V below alt regulator voltage. (NOTE: they can still enter float at different times so this may not always work see #1)

#3 Install a switch in the alt regulator feed to disable the engine alt. If external regulation simply cut the +12V power feed wire to the regulator. If internally regulated see #1... Never open the alternator B+/Output or you may blow the diodes. You disable an alt by turning off the regulator not by disconnecting/opening the B+/output of the alt to the batteries.


This is not really an issue just an annoyance when you lose tach... I run without tach very often as my Li bank charges fast and then the alternator is turned off once the bank is full. Not an issue, just an annoyance.
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Old 29-06-2014, 09:37   #4
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Re: Solar panels disabling tach

Nothing is wrong--If you want to see the tach, just turn on a DC load, like incandescent lights, and it will pop back up again as the alternator kicks in.
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