Can't reach the magic 12v

Iheartbus · 05-17-2017, 09:15 AM

So I have 3 batteries, 2 of them are in parallel with one negative and one positive for the bus. For whatever reason, it reads 12.4 at the battery, but in the bus it only goes up to around 11v or so. Is this normal?

milkmanchip · 05-17-2017, 09:31 AM

I don't think so, I think I would go to A Batteries Plus or auto parts store and have each battery check individually disconnected from each other to see if there isn't a dead cell in one or more of the batteries that's keeping you away from the 12 you should be 13 or better

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Iheartbus · 05-17-2017, 09:36 AM

well we took a voltage meter to each battery once we disconnected it from parallel and both of the batteries showed 12.4. For whatever reason once the engine is on it just reads 11v

milkmanchip · 05-17-2017, 09:41 AM

I'm not an electrical engineer or anything but I know when I took my batteries to the AutoZone they checked it with a battery tester which puts a load onto the battery and revealed a dead cell so I don't know if just checking it with voltmeter would reveal a dead cell or not maybe somebody else with better credentials in the electrical field ..... that was a joke, could help you out better than I

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roach711 · 05-17-2017, 09:44 AM

If I'm reading this right you have 2 12v starting batteries cabled in parallel and a 12v house battery by itself.

If you see 12.4 at the battery and 11 inside the bus I'd be looking for bad battery cables and bad ground connections. It's not uncommon to have what appears to be a good battery cable that is all eaten up inside the insulation.

roach711 · 05-17-2017, 09:48 AM

Quote:

Originally Posted by Iheartbus

For whatever reason once the engine is on it just reads 11v

Sounds like you may have a dead alternator. With the engine running test voltage at the alternator. You should be seeing ~14.5v.

milkmanchip · 05-17-2017, 09:52 AM

I concur with checking the alternator some of these buses came with under-producing alternators and need to be upgraded.

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roach711 · 05-17-2017, 10:07 AM

If you have a diesel with glow plugs your battery voltage will stay low for a minute or so after the engine starts. After the glow plug relay shuts off the voltage should pop back up into the normal range.

We need more details about your engine and how you're testing.

coolbus · 05-17-2017, 10:30 AM

On my bus the batteries are brand new, and until the alternator kicks in my gauge reads a bit low (11 or 11.5 v), I've checked all cables with a multimeter and ammeter to see if I'm leaking current anywhere and it doesn't seem that way, my gauge just doesn't read that accurately, you may have the same problem. Once the alternator is running it pops up to around 14v.

milkmanchip · 05-17-2017, 10:31 AM

Yes my bus alternator has an Exciter which doesn't start producing anything until a certain RPM and then she kicks in.

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Iheartbus · 05-17-2017, 10:42 AM

When I drive it the voltage does not change, gosh I hope the alternator is ok.

I have a DT466E, she's old, 14k hours and 300,000 miles on it, but is still insanely strong. There is probably a lot of electrical issues since they cut out the box when they sold it to me and I have not yet fixed it, everything electrical works in the front but the back brake lights and stuff doesn't work. I'm still trying to fix the box.

roach711 · 05-17-2017, 02:03 PM

From what I've read, the DT466 has no glow plugs so my best guess is that it;s time to test that alternator.

BlackJohn · 05-17-2017, 02:24 PM

Well, I would sit in it and then start it while watching the voltmeter guage or ammeter whichever you have, maybe both. Once it has fired up and running at a smooth idle, after the glow plugs are shutdown or maybe you have a grid heater, not sure, but they are high demand items on right after ignition. Sometimes for a few minutes, others not so much. Then if everything seems normal, turn on every switch you can find in the bus. That will put more load on the battery so the alternator should be outputting to keep up with that loss as well as the staring loss currents. Make note in your mind what you are seeing. Then, start turning those switches off after about 10 minutes, one by one and keep an eye out for changes in your instrument readings. You want an increase on the guages but they are not foolproof. If you are able to, then test for voltage reading at the batteries and from the alternator.

So how are the lights coming along or not?

Keep at it, you'll learn.

Iheartbus · 05-17-2017, 04:53 PM

I have a grid heater, it has a plug in to warm the block up located in the back of the bus. As far as I am aware, no matter how much I rev the engine, the voltage doesn't move at all.

Iheartbus · 05-17-2017, 04:54 PM

Quote:

Originally Posted by BlackJohn

So how are the lights coming along or not?

Keep at it, you'll learn.

I bought a wire stripper and I'm stripping the wiring so I can reconnect the panel they tore out, hopefully once all the wires are reconnected (and hopefully, the right ones) I'll have a better understanding of what, if any, is missing.

family wagon · 05-17-2017, 05:10 PM

A grid heater is in the intake and is powered by the 12 volt system. Looking down into the intake, it looks like a stack of zig-zag plates not unlike the fins on a radiator. It pre-heats the air as it flows into the engine.

The mains plug you spoke of goes to a block heater. That heats the coolant and in turn warms the pistons and cylinder walls. It's different from glow plugs or grid heater which both work to heat air directly, but it works in concert with those for starting in cold weather. There can be a lot of different electrical-powered heaters on a diesel engine!

You could take the volt meter to the output stud on the back of the alternator and measure from there to the alternator case. If you don't have at least 13.2 volts there, and preferably higher like 13.5 to 13.9 volts or even a little more, then either there's a whole lot of load pulling the alternator down or else it just isn't producing like it should. While you're in the neighborhood, disconnect inspect and re-connect whatever connectors are on the alternator.

Just to clarify: do I understand correctly that the battery voltage is lower when the engine is running, even after it's warmed up, than when it's not running?

Iheartbus · 05-17-2017, 05:15 PM

Yes its lower. When the engine isn't running it is around 12.4v, while running the dash says it is at 11.

Ty for explaining the different heaters, I guess its a good thing that I have all these neat things on it for the winter days, cool!

We did take a voltage meter to the alternator and I can't remember what it was but it didn't seem to concern my friend who is an electrician, he didn't have time to fix the issue we were just trying to get home before the cops pulled us over for not having lights, and it was getting dark very quickly. I wish I knew what I was doing but I don't, otherwise i'd just take the wires I knew needed to work and put em together, this box they cut out (which really, really, really, really sux that they did this) is very complicated since the wires are not labeled, and even though they are color coded, there are multiple colors.

Stu & Filo. T · 05-17-2017, 05:25 PM

Just for giggles , disconnect the cable running to your starter solenoid, take a reading & let us know what you have, disconnected one side take a reading reconnect then disconnect the other side take a reading.

Iheartbus · 05-17-2017, 07:06 PM

Quote:

Originally Posted by Stu & Filo. T

Just for giggles , disconnect the cable running to your starter solenoid, take a reading & let us know what you have, disconnected one side take a reading reconnect then disconnect the other side take a reading.

I don't know where that is, but I'll ask the mechanic to do that if I go to one

family wagon · 05-17-2017, 07:17 PM

Are all these measurements taken with the same meter? We can't compare dash gauge readings with handheld meter readings mainly because dash gauges are notoriously inaccurate.

If you've started the bus several times and run it a while without spending any time with a battery charger, then the alternator must be working at least a little bit. The batteries would surely be dead by now if it weren't.

Do we have a handheld volt meter measurement at the batteries prior to start (yes, I think the 12.4 you quoted earlier was done this way) and after running for a few minutes (I'm not sure we have this one)?

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