312-8 with a K301 engine: charging at 16 VOLTS!

[Alrashid2 424]

Hey guys, been a bit since I posted here! Bought my 1980 Wheel Horse 312-8 last October 2024, and have loved getting it up and running. Had a good 6 months or so before a new problem arose!

 

When I bought this, the Voltmeter didn't work so I replaced with an aftermarket. I know when running at WOT it was showing it charging at about 14V give or take. I happened to look down today and saw the gauge was maxing out past 16V! I took a voltmeter to the connections and saw it was indeed charging at around 16.5V, though it was jumping up and down a ton. Engine off, battery is holding at 12.7V. 

 

Had I not looked at the voltmeter, wouldn't have known there was a problem. Running perfectly fine. I love working on engines and mechanical things but electrical is my weakness. I looked at every connection on the engine I could see and everything was tight. Nothing looks to be shorting anywhere either as far as I can tell. 

 

Any ideas here? Is there a simple fix/repair for this? I am concerned 16V is way too high and will fry the battery or some other components. I appreciate the advice guys!

 

Edit: added some photos of every electrical component I could see

Edited 3 hours ago by Alrashid2
Photos

[pfrederi 19,062]

How old is the battery??  Have it load tested...a weak/bad battery will confuse the regulator

[Alrashid2 424]

Hey pal, literally just tagged you on another post back in 2016 I believe where you said yours was reading at 16V! Funny coincidence. Did you ever figure that one out? Mine is doing exactly what you said yours did in your post: starts around 14V but over a few minutes creeps up to about 16V.

 

How do I load test one of these batteries? Or is that something an auto shop needs to do? 

[Handy Don 14,826]

6 minutes ago, Alrashid2 said:

Or is that something an auto shop needs to do? 

Shops and parts stores normally have a load testing tool.

Both will usually test for free in hopes you’ll buy the replacement there. 😁

Of course, you want to witness the testing!

 

BTW, the rationale for load test is that it’s common for a battery at rest (or on a maintainer) to test to a useful voltage but when under load, as when cranking to start, it cannot sustain that voltage. 

[pfrederi 19,062]

Poor mans emergency load test...Hook up your multimeter to the battery should be about 12.6  pull spark plug wire...Start cranking engine voltage will quickly drop..if it goes below 9 volts battery is toast..

[Alrashid2 424]

Thanks guys for replying! I saw Amazon had a replacement battery for 60 bucks, free returns, and could be here tomorrow evening... So I bought it thinking why not?

 

I'll go try a poor man's load test now!

[Alrashid2 424]

Interesting Update!

 

So, I tried the poor man's load test (Thanks @pfrederi!). Voltage on battery was 12.6V beforehand. Pulled spark plug wire, and started cranking for 5-10 seconds. Started dropping and got down to 9.2V. I stopped cranking, and immediately started cranking again. Now in the low 8.0V range and dropping, and starter was slowing down. Stopped as I didn't want to drain the battery too far and have this thing stranded in the driveway!

 

Here's where things get interesting. I was able to start her up after reinstalling the spark plug wire. Running normally, WOT, and now the charging voltage is back to normal at around 14.5V! 

 

Again, electrical is not my strongsuit, but am I thinking correctly in that, the battery was drained, so now the excess voltage is getting "used up" to recharge it? Would this confirm it is a bad battery? I ran it for 5 minutes around the property, voltage never got above 14.5V, and once I shut her down, battery was holding at 12.6V again. 

 

I'll still order a new battery, but wondering if this was some weird fluke, a battery issue, or an issue that will rear it's head again?

[Achto 29,990]

This problem could also be with your regulator / rectifier.

 

Will look like one of these.

[ri702bill 10,197]

5 minutes ago, Achto said:

This problem could also be with your regulator / rectifier.

 

Will look like one of these.

And the actual issue just may be a poor (painted, oxidized, corroded or otherwise compromised) ground at the rectifier to sheet metal mounting bolts.

Many of us add a secondary ground cable from the battery negative terminal to one of the rectifier bolts. It must be properly grounded, at all times while running, for it to do its job...

 

[rmaynard 16,617]

I have found that over charging can be as a result of poor grounding of the regulator. I've had them go as high as 23 vdc. I cleaned the back where the mounting screw goes through, and cleaned where it mounts to the tractor. Problem solved. 

[Alrashid2 424]

Hey guys, thanks for the advice but I don't have a regularor on mine. 1980 model so it has the 3Amp charging system. (Headlights turn off when engine off)

 

Did you guys see my update? Any thoughts on it?

Edited 1 hour ago by Alrashid2

[pfrederi 19,062]

There is no diagnostic for high charging voltage in a 3 amp unregulated system.  How old is the battery??  If it has been starting the tractor OK I would cover up the silly voltmeter and forget about it.  I have a 310-8 with the 3 amp system no gauges (no worry ) she has worked for a long time and battery has held up well...

 

 

 

 

[kpinnc 15,878]

If your system charges high (16VDC) for 5+ mins directly after cranking and then tapers down to 13-14VDC, that is normal operation. 

 

Your rectifier responds directly to the load applied to it, and cranking definitely zaps alot from a battery. It takes a few minutes to settle back down sometimes. 

 

If it charges high all the time, then you have a bad connection or possibly a battery going south. 

[JCM 10,336]

1 hour ago, Alrashid2 said:

 1980 model so it has the 3Amp charging system. 

 

 

FYI     First year for a 312-8 if my memory serves me correct was 1985. A year after the Black Hoods stopped producing.