Ballast Resistor Value?

[Geoff_in_MN]

I located the voltage regulator in my 1972 656 diesel hydro. I installed an alternator after the original one seized up only to find the charging voltage to be around 19.22 volts. Yikes! I'm assuming the voltage regulator is bad but unless there is a way to test it out of the tractor it's relatively cheap. I checked the resistance of the ballast resistor and it ohmed out at 10.22 ohms. My question is, is that within spec?

[snoshoe]

17 minutes ago, Geoff_in_MN said:

10.22 ohms. My question is, is that within spec

Yup should be good.

[Geoff_in_MN]

11 minutes ago, snoshoe said:

Yup should be good.

Thanks. I'm sure this'll be a trouble-free installation. Or not.

[snoshoe]

1 hour ago, Geoff_in_MN said:

Thanks. I'm sure this'll be a trouble-free installation. Or not.

If regulator is the problem. It should be. If wiring harness is not good it could get interesting.

[HydroTek]

Trash the regulator and put on an alternator with the internal regulator 

[Geoff_in_MN]

I could trash the current alternator, but not this time. I'm not a purist when it comes to originality, more function over form. Gonna stay with the current alternator and voltage regulator for now, but not opposed to trying other means. Snoshoe hinted at bad wiring. It's all original and is showing age. We shall see.

[snoshoe]

3 minutes ago, Geoff_in_MN said:

I could trash the current alternator, but not this time. I'm not a purist when it comes to originality, more function over form. Gonna stay with the current alternator and voltage regulator for now, but not opposed to trying other means. Snoshoe hinted at bad wiring. It's all original and is showing age. We shall see.

Should be someone pushing a one wire alt here soon. I would go with the electronic version of the regulator. Personally prefer the 10DN to the 10SI. The mechanical regulator was the biggest problem with the 10DN. The alternator itself was more trouble free than the 10SI. No original parts for either one anymore. Just China replacements so it probably doesn't matter anymore.

[HydroTek]

One wire is not all that good
it drains a little so that the regulator and power up when the alternator is spinning

So on a parked tractor there is some battery drain 

I prefer a 2 wire that is turned off with the ignition key or pressure switch 
for those that spend a lot of time in the shed 

[Geoff_in_MN]

This is what I ordered. Probably solid state. I don't know. 

[DT Fan]

Please report back how that works out. My 756 G is putting out about 17.5 volts and cooking the battery. I have a rebuilt 2 wire internally regulated alternator on the shelf but would like to keep the one on it in place if possible.

[snoshoe]

2 hours ago, DT Fan said:

Please report back how that works out. My 756 G is putting out about 17.5 volts and cooking the battery. I have a rebuilt 2 wire internally regulated alternator on the shelf but would like to keep the one on it in place if possible.

Original delcos had a screw under the cover to adjust voltage. Replacements you had to bend the spring anchor to adjust. In this case pry the anchor up. You will probably go to far. Now use 2 screwdrivers. One as a drift on top of anchor and the other as a mallet to lightly tap it down until voltage is in range. Give it a little time to stabilize between adjustments. Installing cover and how tight you tighten screws will affect final result. So recheck. Battery must be charged to do this or result will be to high. Probably how it got to where it is.

[brahamfireman]

11 hours ago, Geoff_in_MN said:

I could trash the current alternator, but not this time. I'm not a purist when it comes to originality, more function over form. Gonna stay with the current alternator and voltage regulator for now, but not opposed to trying other means. Snoshoe hinted at bad wiring. It's all original and is showing age. We shall see.

Did you install a new alternator or a used alternator? 

I'll 2nd what snoe said and just switch to an internally regulated alternator. I personally like staying with the 3 wire 10-SI, you just jumper a couple wires were the regular used to be and your dash light will even still work. 

External regulators suck now.  Even the electronic regulators do weird things or just randomly die.

We've rebuilt probably 10 internally regulated alternators and so far they're going good. 

[Geoff_in_MN]

2 hours ago, brahamfireman said:

Did you install a new alternator or a used alternator? 

I'll 2nd what snoe said and just switch to an internally regulated alternator. I personally like staying with the 3 wire 10-SI, you just jumper a couple wires were the regular used to be and your dash light will even still work. 

External regulators suck now.  Even the electronic regulators do weird things or just randomly die.

We've rebuilt probably 10 internally regulated alternators and so far they're going good. 

I installed 2 new alternators from DB Electric. Both the 10DN style. The first one went bad within about 5 hours of use. The 2nd one is pushing 19.22 volts so obviously still good even though it got real hot in very short order. I'm hoping a new regulator will take care of that issue. If not, I've probably got some wiring issues I'll need to address. I'll keep everyone posted.

[Matt Kirsch]

16 hours ago, HydroTek said:

One wire is not all that good
it drains a little so that the regulator and power up when the alternator is spinning

So on a parked tractor there is some battery drain 

I prefer a 2 wire that is turned off with the ignition key or pressure switch 
for those that spend a lot of time in the shed 

It's hit and miss with the one-wires. Some will run a battery down in a week, some a month, and others you can leave sit virtually indefinitely. Both Dad's and my Super M's had one wire alternators and they generally sat all winter, fired right up, and ammeter dropped to near zero within a couple of minutes, meaning the batteries were pretty well charged.

On the other hand we had several problems with standard 10SI conversions. On that W-400, the alternators wouldn't last 10 minutes before they'd go crazy and start boiling the battery. Went through four of them. Checked the wiring six ways from Sunday, never found the problem.

[acem]

18 hours ago, HydroTek said:

One wire is not all that good
it drains a little so that the regulator and power up when the alternator is spinning

So on a parked tractor there is some battery drain 

I prefer a 2 wire that is turned off with the ignition key or pressure switch 
for those that spend a lot of time in the shed 

I have had very good luck with single wire 10si alternators.

I believe some conversions will drain the battery and some not. I do know there is more than one conversion methodology. Don't know which is best...

My only problem with the single wire conversion is they tend to charge at a higher voltage than I like (near 15V) and overcharge batteries on long running engines.

[DT Fan]

On 3/21/2026 at 8:27 AM, snoshoe said:

Original delcos had a screw under the cover to adjust voltage. Replacements you had to bend the spring anchor to adjust. In this case pry the anchor up. You will probably go to far. Now use 2 screwdrivers. One as a drift on top of anchor and the other as a mallet to lightly tap it down until voltage is in range. Give it a little time to stabilize between adjustments. Installing cover and how tight you tighten screws will affect final result. So recheck. Battery must be charged to do this or result will be to high. Probably how it got to where it is.

Thanks snoshoe! Your advice is spot on and putting the cover on absolutely changes the value. Enough that I had to walk away. Will try again later.

[Geoff_in_MN]

Installed new voltage regulator direct from China. Initial charging voltage is down considerably from the 19.2 volts. it's hovering around 14.35 volts now, which seems a bit high, but the battery was discharged from having to hold the glow plug button for 90 seconds. I'm gonna keep an eye on things to see if it doesn't settle down a bit.

[snoshoe]

3 minutes ago, Geoff_in_MN said:

Installed new voltage regulator direct from China. Initial charging voltage is down considerably from the 19.2 volts. it's hovering around 14.35 volts now, which seems a bit high, but the battery was discharged from having to hold the glow plug button for 90 seconds. I'm gonna keep an eye on things to see if it doesn't settle down a bit.

Unless this runs 8-12 hours a day without shutoff. Consider anything under 14.5 good. Voltage will only go up as battery charges but should stay steady as it reaches its setting.

[DT Fan]

That's what I was thinking, if I could get it to run 14-14.5 I'd be happy.

[acem]

14.5 is ok.

I've had some run 15V. That will boil a battery out eventually.