Can I retain my 24V gauges?

[Gunfreak25]

So now I have my first electrical question. And yes, I have used the SEARCH button to death first!

My M211 is the Korean era deuce. The truck is your standard 24V early style electrical system. However, my truck has had the original 302 gas I6 pulled and a 455 Olds V8 put in place. The truck was never quite "finished" and currently nothing electrical on the truck works aside from the ignition which is obviously 12 volt. So now, I have a 12 volt ignition while the rest of the truck is still setup for 24 volt with almost all the original 24V 14 gauge wiring in place. It currently just has one 12V battery for the ignition.

My goal is to add a second battery for 24V power and keep everything on the truck stock 24V aside from the ignition which will obviously be 12V. Here's where I can't make a decision. Should I just tap off of one battery for the ignition OR install a 24v to 12v converter for it? I am assuming tapping off a single battery is a bad idea and will shorten the battery life significantly?

My main question however, is the gauges. They are the original 24volt gauges and I really want to use them. But, how in the heck can I use the stock 24V gauges with the sending units on the 455? The only electrical sending units I can find are for powering idiot lights, NOT gauges. Am I going to have to replace them with aftermarket 12V gauges?

Heck, if I could i'd like to just convert the entire truck to 12V. I guess it's already halfway there. My main concern is the wiring, 12V puts out significantly more amperage than 24V and I am afraid of frying something. What will be the easiest/cheapest method for me to get everything working properly and safely?

And if you couldn't already tell, my knowledge of electrical components is still pretty slim. I am learning more stuff everyday though!

 

[woodywood]

you could get sending units from a old 211 engine and use worst case scenario you would have to get adapters most engines have standard pipe threads on the outlets
or you could go with aftermarket gauges change you light bulbs and make it completely 12 volt
i disagree with 12 volts pulling more amps than 24 if that was the case you could buy a 12 volt welder haven't seen one yet only 24 volt ones

 

[Gunfreak25]

I never thought of that! I know where I can get some original sending units from an old Military 302 M211 engine and sending unit bushing kits are easy as pie to find and very cheap. I suppose if I want to retain my stock gauges and 24V system option A is the way to then.

So If I go with option B and just make everything 12 volt are you sure I won't fry anything? The wiring in the M211 is 14 gauge if that matters.

Can anyone else chime in on the 24V amp vs. 12V amp?

So I guess it boils down to cost.....

 

[doghead]

You could add a second alternator with an isolated ground! Then you could have a working 12v and 24v system, like a cucv has.

 

[woodywood]

ask anyone here who has had a loose connection at the battery nine out of tend times it burns the post off the battery my buddy has a suburban and every time i see him i have to pop the hood hold the hot wire(that i repeatedly tell him to tighten up!)so it will start

 

[Gunfreak25]

Well I guess someone before me had an idea similar to mine. The truck still has the original 24V generator and regulator. Which means all I need is to pickup another 12V battery, power converter to keep the ignition 12V, some M211 sending units and adapter bushings, and possibly a few replacement 24V bulbs for my lights.

For under $200 I'll have a stock 24V electrical system with a 12V ignition. Simple and cheap! I may also pickup a relay for the trailer assembly so I can also hook up to 24V and 12V trailers.

I'm getting the hang of this electrical thing. Must run in the family. My great grandfather was a certified electrician and was even assigned to the Manhattan project, we still have his shirt pin!

 

[jasonjc]

Sorry but Omh's law state's Watt's / Volt's = Amps. So some thing running 24v will use half the amps as on 12v.

 

[Gunfreak25]

That's exactly what my grandfather told me and is why I am going to keep only my ignition 12V.

General question, the 12V battery that's been in my truck for the past few years has been staying charged via the 24V generator and regulator. Does this just cause the battery to charge slower or would it cook the battery? I have a feeling i'll be needing two batteries from the auto store.

 

[Jake0147]

Same as with your light bulbs. Volts sets the "pressure", resistance sets the "flow". With the bulbs, you can envision a twelve volt bulb is going to be a bright sun of a gun for about five seconds... A battery provides resistance to a circuit that is "powered" by a higher voltage source. Half as many batteries (in series) is half as much resistance to current flow. Too much current. 24 volts across a twelve volt battery means fuming and bubbling shrapnel all over your battery compartment. It might survive that for some time, if it never charged that way very often, or for very long at a given time with adequate cooling/equalizing time in between. Check for an adjustable regulator that may have been backed off some. Or a generator that's been molested by the local auto electric shop...
Get out your volt meter, disable the generator, disable the engine from starting, and whatch the battery voltage as you crank the engine. Does it still perform? Now, re-enable your generator and ignition system, and verify what exactly the generator is producing. Then you will KNOW what you have. It's custom made, take NOTHING for granted.

FWIW, if I were taking on this project, since originality is out the window anyhow... I'd really look into a couple of single wire alternators, one of which will require an isolated ground. (Those of course have two wires, but the starter shop I use still calls them "single wire", I don't know if it's right, but that's why I go see them... Perhaps "self exciting" would be a better term?) Anyhow, they're not that uncommon, and a local auto electric shop can make several recommendations about specific models in which this is an option. The bottom line will be a much better balanced system than trying to string a twelve volt helper inside of a twenty four volt system, and you won't be running your main propulsion from a converter box. Somehow, however functional it might be, that just doesn't seem right...

 

[Gunfreak25]

I appreciate the information Jake, will do the checks when the truck arrives. I was thinking the same thing, perhaps they toyed with the regulator and or generator? I will have to check!

I really don't see running the distributor off of a converter box as being a problem. Would this classify as being "jerry rigged"? What if I just just ran the ignition off of one battery and then used an equalizer to keep things in balance? I suppose that would be a better alternative?

 

[m16ty]

I've installed a civilian ignition on m7 M715. At the moment I'm running the coil through a 24v/12v converter but I've been wanting to try something.

From what I understand, most 12 ignitions run on 6v. This is done either with a coil with a built in resistor or a standard coil with a external resistor. My thinking is, if I run 24v through a external resistor and then to a coil with a built in resistor. That (in theory) should send the required 6v to the points. I haven't tried this yet so I have no idea if it will work for sure.

The starter is another issue. I've changed 6v tractors over to 12v using the factory 6v starter without issues. I wonder if this would work with a 12v starter running on 24v?

Doesn't the M211 use standard m-series gauges? If so, any m-series sending units should work.

If it were me, I'd just try and leave everything 24v if I could but that's just me.

 

[Gunfreak25]

I have heard of running 12V starters off a 24V system without any issues. It would probably start REAL easy. But if you are having to crank it over for anymore than a few seconds (cold weather starts) i'd just use a 24V starter.

The M211 does use standard M series gauges but I am willing to bet the sending units/gauges operate at slightly different ohme levels. Using A2 gauges might result in false gauge readings. Since I will be keeping my electrical system 24V my fuel sender and air pressure sender are still in the truck and should work just fine once they get the proper voltage in them. I will have to order a temp and oil pressure gauge from Alfa Heaven though and some standard size bushing kits to adapt them to the 455. Shouldn't be too hard, and both senders are only about $20.

Although I like the idea of a single wire (self exciting) alternator, that's another $100 I don't feel like dropping into an already expensive money pit. Unless my alternator/regulator has been toyed with too much, in which case I'll go with a new 24V single wire alternator. These are utilitarian vehicles and almost never have any accessories on them. Mine has ZILCH and the only thing I will be running off of the converter aside from the distributor will be a radio with some small speakers. A 10 or 15 AMP converter should be more than adequate to do the job. The only thing I will have running off the stock 24V system will be the lights and gauges. Maybe a turn signal kit later.

 

[m16ty]

The M211 does use standard M series gauges but I am willing to bet the sending units/gauges operate at slightly different ohme levels. Using A2 gauges might result in false gauge readings.

I don't think so. A m-series gauge is a m-series gauge. They are made the same for the sole purpose of having only one set of gauges for all vehicles. If they are in fact m-series gauges they are the exact same gauges that are used in the M35A2 and any other m-series vehicle (ok, except the m880 and the cucv). as long as you use a m-series sending unit (off of any m-series vehicle) you should be as accurate as a military gauge can be.

 

[Gunfreak25]

Hmm, maybe your correct then? I did some searching and the oil sender for the A2 series even installs the same way as on the original 302 GMC gas engine (side of engine oil gallery).

I guess the better question would be, will an M series temp and oil pressure sender fit onto the 455 Oldsmobile without too much trouble?
I wish I knew what the thread size was for my engine. It's a 1971-72 455 Olds that came out of a Delta 88.

 

[m16ty]

I guess the better question would be, will an M series temp and oil pressure sender fit onto the 455 Oldsmobile without too much trouble?

I would say yes. You may have to run to the hardware store and pick up a few pipe fittings but that's all.

 

[popacom]

Hey guys!!! I built a bunch of M-715's up in the past and the way I got around this issue was using a 12Volt starter(Just limit crank time to no more than 5 seconds) and use a HEI distributor(Which needs to see 12V and above) with a dropping resistor with a value that drops voltage to around
13-15 volts and you can keep all the rest of the truck 24V. I am sure I will get arguments on this one but I did it more than once with no negative results.

Thanks!!! popacom /BILL in Ky.

 

[Gunfreak25]

HEY! I like that idea! My truck already has a 12V starter in it that's original to the motor. So the HEI can take on full 24V power but only delivers 12 to 13 volts? Does it have some kind of internal voltage converter or what I think you called a "resistor"?

Would this work on mine?

KMJ Performance :: IGNITION :: OLDSMOBILE :: Oldsmobile V8 HEI Distributor 307 330 350 400 403 455 OLDS

 

[popacom]

The resistor is a ballast resistor in this application. The resistor goes in line with the 24V lead that
originally fed the waterproof dist. on the GMC engine 24Volts >into the resistor,which drops the voltage to as I said around 13-16 volts which the GM HEI dist. will tolerate very adequately.
All the sending units for your original gauge's can be screwed into existing ports on the engine you
have in the truck now(Water temp,oil pressure) hope this helps you out. It's about the simplest
and least expensive way to make engine swaps work on the vehicles I have done myself.


P.S. since the engine is not original,I would use a later internally regulated 24Volt military alternator,as they are more plentiful and
less problematic than some of the split systems(Such as the one used on the CUCV trucks ) and you will pay about the same price for them (with a little careful shopping) as you will for one of the two 12V units required to run a dual 12 alternator system,
That's my thoughts on the problem.


popacom / BILL in Ky.

 

[Gunfreak25]

Thank you to everyone for your opinions and input on my questions.

I like your idea Bill, and you are correct. The cheapest and by far the easiest and least problematic setup I can go with is just a single 24V Military alternator connected to 2 batteries wired in a series. A 15 AMP converter for the ignition, cd player and some small and simple speakers should do the trick perfectly. If I shop around at the local Military salvage yards I bet I can do it all for under $150 too. Even if I went with dual alternators for 2 seperate power supplies, i'd still be using a converter for my gauges and other 24V stuff. So it boils down to what I want to run off a converter box. The ignition or my lights and gauges. I say ignition. I can always go with a higher amp box later too.

I am guessing the standard and most common thread size for sending units is 1/8" NPT?

I've included a couple pictures. And yes, the intake does have the proper air cleaner and a much newer/cleaner carb on it since that picture. I still need to mount the compressor for air assist power brakes. Luckily I have LOTS of room under the hood and I may be able to use that old AC compressor bracket for my monster size air compressor. If all else fails I'll go with a hydravac!

 

[kc5mzd]

I like GM HEI ignition, but if you don't hook up the resistor properly... well just make sure the distributor comes with a warranty...
Also you might think of getting a 24 - 12v converter and use it to power your radio, gps, cell phone charger or other small 12v electronic equipment you haven't thought of yet. You could hook it to the HEI distributor and even the coil side of your 12v starter solenoid.

Your best bet would be go to an alternator shop and get a dual output isolated ground alternator. I had one on an old RV that had separate batteries for starting. It worked very well and would be easy to setup to charge your 2 batteries separately. Then you could just hook the 12v accessories to the first battery and the 24v stuff to the second.