Voltage drop on 24V system

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kim

kim

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Maple Ridge, BC, Canada
I have noticed in the last few days that the voltage will not register on the meter, or will register and then drop from ~20V down to nil, when I turn the key to on and wait for the glow plugs to heat. The juice is there as this happens intermittently.

It seems to me that there must be a short or something. Any ideas on where to look?
 
Alternator would be my first suspect...maybe the brushes are starting to go.

With the truck off, check the individual voltages of your batteries and see what they are. Also, you're not drawing 12V by tapping off of your low side battery without an equalizer, right?
 
When the vehicle is running, the altenator is charging just fine, the meter never drops. It is only prior to start, typically the first start of the day, that this happens.

No, I am not tapping off either battery for any 12 volt needs. I will test my batteries but have not done so yet because I know the power is there.

By the by, do you know where I can pick up 24V tube fuses for the 24-12V converters?
 
kim said:
When the vehicle is running, the altenator is charging just fine, the meter never drops. It is only prior to start, typically the first start of the day, that this happens.

No, I am not tapping off either battery for any 12 volt needs. I will test my batteries but have not done so yet because I know the power is there.

By the by, do you know where I can pick up 24V tube fuses for the 24-12V converters?
Click to expand...

Okay...I'm confused now. I thought in your original post, you were stating that sometimes while your vehicle is running, the voltage meter shows a drop in voltage? Now, you're saying that this only happens when you first start your vehicle for the day?

If what you're describing is that the voltage meter is showing a lower reading right after starting your vehicle, and then the needle kicks up to a higher (usual) reading after the truck runs for a couple of minutes, then this is just your voltage regulator kicking in.

As far as I know, the fuses are all the same whether for 24 or 12V.
 
Clean your battery posts and look at the ground cables for corrosion(green).

Could be your batteries are just getting weaker. When the glow plugs are on they will drop a bit. But if it goes lower than 20 your batteries must be weaker. Especially if this is just your first start of the day.

Dirty connections will also act like a weak battery. So will corroded battery cables. They act like a resistor lowering voltage.
 
Stone I understood his orginal post as when he turns the glow plugs on first thing in the morning that it drops the voltage more than normal. I did not read running into that. Or after start.......
 
"...then this is just your voltage regulator kicking in.</i>

Sorry for the poor explanation. Let me try again.

Vehicle not running, turn key to 'on' and wait for glow plugs. Voltage usually goes to about 20v at which point you hear the voltage regulator (I assume that is what 'clicks'). At this point you would engage the starter. However, sometimes while waiting for the 'click' the voltage drops to <16V, just as if I turned the key off. In this case, I start the truck and voltage returns to normal ~28V running condition after running for about 10 seconds.
 
kim said:
"...then this is just your voltage regulator kicking in.</i>

Sorry for the poor explanation. Let me try again.

Vehicle not running, turn key to 'on' and wait for glow plugs. Voltage usually goes to about 20v at which point you hear the voltage regulator (I assume that is what 'clicks'). At this point you would engage the starter. However, sometimes while waiting for the 'click' the voltage drops to <16V, just as if I turned the key off. In this case, I start the truck and voltage returns to normal ~28V running condition after running for about 10 seconds.
Click to expand...

I won't assume, but I what I think your hearing is the glow plug relay disengaging.

Voltage reg doesn't become active till its running. And don't make noise to my knowledge.

Your batteries sound weak if its dropping that low. I would guess the voltage reg is fine since you get 28v when running.

You might have something staying on over night like a dome light or something like a converter drawing voltage. Do you know anyone with a clamp on AMP meter?

Or disconnect the negative posts for the night, rehook in morning to see if they drop that low again. Could be a lot of capacity is drained off overnight. That would rule it out. If it still went low I would guess the batteries are ending the service life. And you are observant enough to see them go :)
 
I will check the battery voltages this evening. I replaced them about two years ago. There is some corrosion, which I have cleaned off but it has reappeared fairly quickly. Is there some goo/product that you would recommend that I apply to these connections?

As far as something being on overnight, I don't think so. I have no fuses in my converters, dome light is off, no stereo right now...

I am starting to suspect that it is a connection issue or a glow plug/relay issue. Is there a way to test these?

Thanks a million! This site is awesome.
 
This is most likely from a bad ground. I just had this problem with my HJ60, and what fixed it was putting in new ground wires from the batteries, and I also added a few new grounds to the fenders and to the fire wall. There was a lot of resistance on the old ground wires. It can actually be dangerous if you have a bad ground because something else will ground, and if it's too thin, it can heat up and start a fire.
 
Just make sure all the connections are clean. I have heard replacing battery cables and going one size larger is very beneficial. The toyota ones seem soo skinny to me. If you unhook the battery cable and feel it for flexabilty, if it feels like a noodle I would say the wire is too broken down, or corroded. It should have some rigidity. If you bought a new cable from the auto store it would feel pretty stout, not all whippy.

For the glow plugs, There is a ohm check in the FSM. But My 3b book only says 24v glow system(not specifically hj). It put the resistance at .8 ohms and 1 ohm. Use a good meter that 0's when the probes short out to each other. As you are reading low resistance for most meters.

In the fsm it lists hot resistance per glow plug to be about 4 ohms(I am picking a mid number) So take 6 glow plugs in a parallel circuit that equals .666666 of an ohm. With 24 volts and .6666666 of a load the amperage is about 36.

Keeping that in mind if you had a glow plug that was more than the 1 ohm cold, say it was 3 or 4, it would lower the amperage and you would draw less juice. But if the glow plug was under 1 ohm cold, say .3 of an ohm it would draw incredible amounts more of amperage.

When the glowplugs start, they draws around 170 plus amps, as the glow plugs instantly heat up there resistance goes x4. And settles in arount 36amps( 6 plugs,24v)


So I would start by pulling the busbar(connector bar) off the glow plugs and measuring each one cold from the tip to the block for resistance. First ensuring the meter is going to 0 prior to connecting. If you have a low one that could be the villian. :)
 
I had some issues both with glow plugs (on my BJ43) and electrical circuits (HJ60). Broken glow plugs usually result in excessive black engine smoke after the first cold start (in the morning), but the problem you are describing seems related to batteries to my opinion. The click you are hearing is indeed the glow plug relay disengaging (what Brownbear was explaining), but I propose that you try and see what is happening when you start the engine before the end of the warming-up period (when the enigne is hot). So just don't wait for the end of the warming up but start the engine immediatly. You should see the volt meter needle jump up together with the click of the glow plug relay, even when the engine is running. You could then compaire the voltages during warming up with and without the engine running. A considerable difference (much lower without engine running and so batteries charging), could be related to weak batteries. And after 2 years of service life, this could be possible, especially in colder climates or when you overcharge the batteries (which you could smell under the hood usually).

I had another problem also with my voltage meter that went down, but then all meters on the dashboard went banana's: engine temperature was beyond red, fuel tank was empty, oil pressure was gone, etc. However, this was related to a short circuit inside the meter panel so it was only a minor problem. Nevertheless, this happened in the middle of nowhere here in the jungle of Suriname, so it wasn't very funny...
 
Great to find it. Also wouldn't be a bad time to go thru the battery cables for condition. Get them good before winter.
 
I just replaced all my battery cables and connections. I used brass marine terminals with 1 gauge wire. I also added a new cable from the alt directly to the battery.

For cables, I replaced stater wire, neg to body, neg to frame, frame to engine block and bat to bat. All using ring ends soldered on.

My electrical has never been better.

Oh, and if you are still running 12V headlights, make sure that both are working properly. Or do what we have done and replace them with a 24V system to get around the 12V tap on the bats.
 
No.

On my brothers HJ60 we switched the headlights out to a 24V system. We did this by making a new harness and adding realays so that the trucks 12V headlight harness is not used.

Basically you use the trucks switching leads for the headlights to activate relays that are attached directly to the 24V side of the batteries. I think he may have lost his high beam indicator in the process, but that can be worked around if need be.
 
The Dude said:
I just replaced all my battery cables and connections. I used brass marine terminals with 1 gauge wire. I also added a new cable from the alt directly to the battery.

For cables, I replaced stater wire, neg to body, neg to frame, frame to engine block and bat to bat. All using ring ends soldered on.

My electrical has never been better.

Oh, and if you are still running 12V headlights, make sure that both are working properly. Or do what we have done and replace them with a 24V system to get around the 12V tap on the bats.
Click to expand...

1 gauge eh, sounds good. Do you know off hand what the stock size is? I know its pretty light.

There are tonnes of websites that have a voltage drop calculator on them. You can imput the load and then pick and play with different size wire to see what the voltage drop difference is. having larger gauge wire the voltage drop becomes almost nil.

But trying to squeeze the voltage thru lighter wire you really notice a drop. Just rewiring the headlights with there own harness would make a world of difference for brightness, going up in gauge. Then if you wanted you could run higher watt lights.

Here is one of the voltage drop cals... http://www.csgnetwork.com/voltagedropcalc.html
 
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