What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Alternator output voltage

Ed_Wischmeyer

Ed_Wischmeyer

Well Known Member
The first automotive alternator (Suzuki) lasted about a thousand hours before it went belly up. It was replaced with a rebuilt one that lasted about 50 hours before it failed in flight. And, of course, when it went to the shop, it worked just fine. Not to worry, I had a spare (new) on hand, just in case.

The new one works, but whereas the previous ones showed 14 volts in flight, this one shows 13.6 - 13.8 volts in flight. (I'm not sure how accurate the voltmeter is on the G3X touch, or if there's an undocumented diode somewhere in this installation, or...)

Is this normal tolerance? Anything to be concerned about, other than charging in flight would be slower than at a higher voltage?

The local shop lost their electrics guy...

Thanks!

Ed
 
Last edited:
On my G3X, I run the main voltage to one of the Volt inputs and for the backup buss I get the voltage from the power input. In theory both busses are the same voltage, but the Volt input reads .3 volts higher than the power input, presumably from the diodes used there to share two inputs.

Back in the 70's, a 13.8 - 14.0 float was thought to be correct. Today we know better and float them around 14.4. That is for flooded lead acid and sealed lead acid likes another .1 or .2 for it's float. I have an adjustabl VR and run it at 14.4

Put a volt meter on the battery with the engine running to see what it is actually putting out.
 
How old is your batt? I am on 400 hours with my Denso and it is always about 14.2 volts after a minute or so of charging.
 
Battery is not old -- don't have the logs at home, but this phenomenon only showed up with the new alternator on the most recent flight. Before that, no problems.
 
Regulators don't all have the same voltage set point. I could doubt your G3X is off, unless the wiring got messed with. Since the original alternator was likely built in a Denso factory, and the current ones are a "will fit" factory, the same life would not be expected.

To your query, In the old days, with flooded PbA batteries, the spec for the industry was 14.0 plus/minus 0.2 volts. That has changed, and specs are up to OEM application likely to match battery technology as Larry mentioned. You might talk to an alternator shop to see if there is a regulator with the same form factor but higher set point voltage available. It could be the easy answer, unless this alternator has tested differently in the past.
 
Last edited:
Ed_Wischmeyer said:
The new one works, but whereas the previous ones showed 14 volts in flight, this one shows 13.6 - 13.8 volts in flight. (I'm not sure how accurate the voltmeter is on the G3X touch, or if there's an undocumented diode somewhere in this installation, or...)
Click to expand...

Ed - I just chased a low volt situation and found a bad connection that looked fine from the outside, but was dropping .5volts. If you have 2 alternators showing low volts, check your wiring - it fooled me till the guys here schooled me.

I did a write up last week...

Good luck!
 
Ed_Wischmeyer said:
Battery is not old -- don't have the logs at home, but this phenomenon only showed up with the new alternator on the most recent flight. Before that, no problems.
Click to expand...

So, assuming you have an alt with an internal VR. It is possible that this is resistance in your wiring, but the circumstances point more to just a cheap off shore VR installed in your Alt that wasn't QA tested for its voltage set point. If after intstallation you got 14V and then down the road, dropped to 13.6, then I would add wiring issues to your diagnostics. Just put a meter on the B lead of the alternator and start it up. If you get 14V there, then you have a wiring issue. I suspect the VR has an OEM spec of a 14V set point, as it is from the early 80's. You can return it and get an externally regulated version of the Denso alternator (I prefer these) and get a nice Transpo VR ($75) that has a trimmer for setting whatever voltage you want. Or just take it back and swap for another one and tell the retailer the the Alt is defective.

A 13.6 buss voltage is going to keep your battery from reaching 100% charge,but should get it to 85%+ and that should be enough to keep it from sulphating due to under charged storage.
 
Last edited:
B&C Alternator

External VR, is, has been set to 13.8 fir 31 years. My PC680 batteries last and last…..5+ years, then I pull for mower, jet skis etc. Standards change, but I personally don't think this is an issue. YMMV.
 
You must log in or register to reply here.
Back
Top