M818 battery switch acting up, voltmeter

[OPCOM]

In the 818, I turn the battery switch ON and there is something odd going on. This is the main power switch for the truck I assume.

Normally, when on, the voltmeter should read in the low green, and after starting, the voltmeter should read higer in green, as it is charging.

What I am getting, beside an intermittent switch, which i have to flip back and forth a few times, this s getting worse too.. is that when I turn the power ON, the voltmeter reads in the yellow, and during starting, the truck cranks properly, as fast as usual, and once started, the needle is just into the red on the voltmeter, but I am finding the batteries not being charged properly.

I suspect some kind of open or high resistance connection between the voltmeter, alternator, switch, etc. I understand this switch has several terminals, not "two" like any sane person would have designed, and then used relays.

Has anyone seen this kind of thing? Bad switch?

I will be checking the schematics in the manuals before too long.

Thanks,

 

[timntrucks]

my 816 does that sometimes. im starting to believe its the black box on the fire wall

 

[73m819]

It IS THE "PCB"Protecive Control Box, time to rebuild or replace

 

[OPCOM]

The schematic shows that it is a box full of relays and maybe two diodes, hard to see on the diagram. I suspect they are more like aircraft style contactors inside, but the box does not seem to have screws on it (it was dark when I was looking)

It makes sense because today it cranked intermittently, and cranking control is through that box. As is the voltmeter power.

Its confirmed with a clamp-on DC ammeter there's no charging going on.

The truck is on the old-school LaMarche mains powered charger now, a nice slow 5A to gently refill the batteries all night. This charger is interesting, high-tech for its time, because instead of just a transformer and rectifier, it has other components like a saturable reactor that end up giving a pulsating charge until the battery is almost full, then smoothing it out to a trickle.

Maybe someone has drawn the control box internal schematic from their own inspection.

So do I have to cut it open or is it soldered together?

It's CARC, I am not sure how wise it might be to try to unsolder it if it is in fact a can. OTOH, if its bad I would enjoy repairing it. Maybe I should buy a new one and fix the old one as a spare.

 

[73m819]

CRANETRUCK did a rebuild on one of these plus a great write up, along with a internal schematic, you can use a 900 PCB on a 809, but NOT a 809 PCB on a 900

Don't see why a bypass can't be built with just a MASTER solenoid, there is no need for a oil pressure safety interlock, ect. the engine start switch controls the fuel solenoid and the starter, this drew power from the master solenoid. I have run many cranes that have the same 855, these have the basic starting system --a on/off master switch and a start button

 

[cranetruck]

Hi Patrick, yes you will have to cut it open. I have used a hack saw and keeping the cut shallow will prevent damage to the insides.
I have also rebuilt a couple eliminating the PCB to simplify the unit, but also eliminating the low oil pressure protecting feature in the process.
The contactors are automotive types...

 

[OPCOM]

I see the two big relays, but there appear to be three in the schematic.

 

[OPCOM]

I'll place a want ad in the classifieds for a new one. I'd take a known good one from someone I know. The rebuild can wait on my pleasure.. I have to do the Veterans day parade.

I have a box of those solenoid type relays from aircraft surplus.

 

[cranetruck]

I see the two big relays, but there appear to be three in the schematic.

It's on the PCB...

 

[OPCOM]

A brand new control box protective should be here this week. The prices are sure all over the map on these things. It's black and new production surplus, but I can live with that

I wonder if it is the little relay that went bad.. not to blame it because it's small though.

My guess from the non-charging and funny voltmeter behavior is the bottom relay in the partial diagram attachment.
Colored pencils are your friend. Colored electrons are your friend too.

If I had a really good 600DPI scan of that diagram, I'd color it and print at Kinko's on a 24" paper roll. haha it'd be 8-9 FT long but a real pretty sight.

Meanwhile, I charged the batts. 25.12V rested. Could take a little moe but why push it. Day and night, how the ol' Speed Queen cranks with a charge on her. That's the temporary name for the M8109. I'm having trouble naming the beastie.

I used to call the M35A2 the "filthy ...." , after the run down fishing boat in 'cabin boy', but i couldn't bring my self to stencil something like that on, it wouldn't be proper, and then I really came to love that ol' truck after spending almost 15Kmiles with 'er roaring along the blacktop.. Miles will do that. Maybe I could start a thread to name the M8109.

As long as that diagram is here, can anyone confirm if the cold start lamp should be 6V or 12V? The glow plug is a 6v one.

 

[73m819]

What I would like to find is burnt up or dead PCB, just looking for the plug end with plug, want to try to build a simple start control like what was on the 855s in the cranes that I ran. Need the plug end and plug to adapt to the military wire harness. I DO NOT see the need for the sealed PCB, If you CAN NOT hear a 250 running, you have NO business being in the truck.

 

[OPCOM]

A dead box should be cheap enough to find. There's the plug. I don't know how hard it is to cut open, but the plug might come off with rivets and come far enough out to cut the wires off, then you can clean up the connector and reuse it.

For my part I do want to keep the anti-starter-engagement function. No reason not to, I don't 'need' it, but why remove a simple thing that could save damage from an idiot? There are many idiots, some day one of them could find his way to the cab.. Or a child, or anything can happen. Heck i was even thinking of adding logic to kill the engine if there's no oil pressure. I won't be doing anything so darn critical that I'll blow the engine for lack of oil pressure just to get that done. OK, and I could add a "battle bypass" switch as well.

In any case, have you determined how to waterproof the box you will make up? I'll never ford my truck to that depth..

 

[73m819]

Using a sealed master solenoid, the way things are set up now using the PCB, you can not push start or roll start the truck if the fuel control on/off valve decides to give a problem unless you screw in the thumb screw, but if the fuel on/off solenoid only burps every now and then you have to step on the clutch till the engine stop rotating, then use the start switch, is you are fighting low batteries, this can become a problem.

They make Murphy switches that shut down a engine that loses oil pressure, this works very simple, the shut down hot wire goes though the Murphy switch, at a pre set low pressure the contracts open and the fuel is shut off. the units that this is mounted on have a start by pass switch. ALL the cranes that I have run have Murphy switches, both for oil pressure and water temp with emg. by passes

 

[OPCOM]

The new control box fixed it. Also straightened up the fuel gauge which had been acting funny, reading high.

I might as well say where I got it, because it was the right part, works perfectly, and was at the best price I found or was offered for an apparently brand new part in the original box. I got it from http://eriksmilitarysurplus.com/

 

[doghead]

The GP dash indicator bulb is 7 volt, part number ms15572-1.
https://www.interlight.biz/light-bulb/55

 

[OPCOM]

wow. they have all kinds of other interesting lamps as well!

I need one to find out if the glow plug heater/igniter is working. I replaced the plug some time ago and read 6V on it, but despite confidence it is squrting diesel in, I can't say I have ever known if it is lighting off the fuel there in the manifold. Wish I could be sure.

 

[OPCOM]

Using a sealed master solenoid, the way things are set up now using the PCB, you can not push start or roll start the truck if the fuel control on/off valve decides to give a problem unless you screw in the thumb screw, but if the fuel on/off solenoid only burps every now and then you have to step on the clutch till the engine stop rotating, then use the start switch, is you are fighting low batteries, this can become a problem.

They make Murphy switches that shut down a engine that loses oil pressure, this works very simple, the shut down hot wire goes though the Murphy switch, at a pre set low pressure the contracts open and the fuel is shut off. the units that this is mounted on have a start by pass switch. ALL the cranes that I have run have Murphy switches, both for oil pressure and water temp with emg. by passes

By Murphy switches do you mean from this company?
http://www.fwmurphy.com/
They make engine electrical stuff.