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Author Topic: A ? for the Electrical Smarty Pants on this forum.  (Read 2414 times)
zubzub
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« on: April 20, 2008, 06:06:39 PM »

Just read a thread  all about different diodes etc so I know there are a few of you that will have tons of knowledge on this one.
I have a '53 4104 that has the batteries set up as neg ground.  That doesn't mean the bus was changed to neg ground, just that somebody has the batteries set up that way.  As far as I'm concerned, given the guages all being wonky (seem to run full on instead of full off wiht the switch in engine run ), the gen not charging, and various other electrical gremlins snarling and growling all over the place (even the engine run  and kill switch is on the AC panel) maybe it is still pos ground with the batts in backwards. So this is what I want to know.
1.  As nothing is working right anyhow, what harm could I do if I try reversing the polarity of the batts?
2.  Is there some other way to work out if they (some PO) have or have not mucked this up?
3.  What exactly is the problem with positive ground system anyhow?  I know it is notused anymore, but electricity is a  weak spot for me so a little theory would do me good.
4. Would batts in the wrong way actually lead to my batteries being rapidly drained  when the engine was running? 'cause that seemed to be happening and I was running a gas gen to charge the batts as I drove (very unpleasant experience).
Finally, I am still 1000 miles away from my bus so I need more theory than anything else right now, I can't trouble shoot from my computor,
as always thanks for the input, Patrick.
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Nick Badame Refrig/ACC
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« Reply #1 on: April 20, 2008, 06:15:36 PM »

Hi Zub,

It's quite possible that when your bus was changed over to neg. ground, they could have used the wrong diods or, the diods could have failed

since then causing your numerous gremlins. There is good reason to keep the neg. ground mostly for modern appliances, lights, and gauges.

Finding the positive ground electrical devices could prove to be costly, and could take longer then normal to recieve them.

Good Luck
Nick-
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« Reply #2 on: April 20, 2008, 06:32:50 PM »

If Set it up pos ground it will be only for a short run, also then the guages would work without me needing to install new ones...come to think of it that may explain why I couldn't get a neg ground temp guage to work....at the time I never even thought that maybe someone had messed up, so I didn't check for it...i guess I also need to know what damage driving a pos ground bus with the batts in backwards would cause.
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JohnEd
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« Reply #3 on: April 20, 2008, 07:01:42 PM »

Your starter will run backwards and the 2 cycle WILL run backwards.  That isn't ok with the engine and the thing will have only one slow forward gear and 4 reverse gears but be rather quick backwards down the road.

John
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zubzub
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« Reply #4 on: April 20, 2008, 07:12:46 PM »

well that's not happening,. starts and runs well, 4 forward gears.  guages left no power and far right when the ngine is switched on.....
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Sean
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« Reply #5 on: April 20, 2008, 07:14:27 PM »

Your starter will run backwards and the 2 cycle WILL run backwards.


The starter will not run backwards.  Starters use wound field, not permanent magnets, and turn in their designed rotation (CW or CCW) no matter which polarity energizes them.

zubzub:

You may have multiple problems here.  I would definitely not reverse the batteries without an answer, nor would I run the bus.  Her's how to find out for sure:

1. Turn off or disconnect all non-essential items.

2. Start the bus.  I assume from your question that it does start and run.

3. With the bus running, carefully disconnect the ground cable from the batteries.  The batteries are now "out of the circuit."

4. Turn the headlights on (this is to provide a non-voltage sensitive load on the alternator for the next step).

5. Take your voltmeter and measure between the remaining battery cable (the one coming from the alternator) and the frame.  If the voltage reads alternator positive and frame negative, you have a negative ground alternator.  If it reads frame positive and alternator negative, you have a positive ground system, at least with respect to charging.  If it reads zero, check back with me -- we'll need to find the regulator "sense" lead and get it connected in the right place.

If you do find that the charging system is set up for positive ground, you'll need to systematically check everything else to make sure it's compatible with that system before fixing the battery problem.

HTH.

-Sean
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« Reply #6 on: April 20, 2008, 07:18:32 PM »

3. With the bus running, carefully disconnect the ground cable from the batteries.  The batteries are now "out of the circuit."

4. Turn the headlights on (this is to provide a non-voltage sensitive load on the alternator for the next step).


Sorry, my bad.  Reverse these steps -- we want the load (headlights) to be connected before we disconnect the batteries.

-Sean
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zubzub
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« Reply #7 on: April 20, 2008, 07:19:23 PM »

thanks very simple solution...
now since I can't check this for a bit and since we are on the subject
"If it reads zero, check back with me -- we'll need to find the regulator "sense" lead and get it connected in the right place."
I'm up for the next step just in case and because I will learn more about the beast....is the "sense lead' the field line?
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Dallas
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« Reply #8 on: April 20, 2008, 07:31:23 PM »

Why not just cut to the chase and flash the field?

Sounds like when they reversed the batteries they didn't flash the field to the generator.

Make a jumper wire and connect it to the "F" terminal on your generator. now, with the other end QUICKLY touch the BAT+ terminal.

Do the same for the second "F" terminal if you have one, some didn't.

Start the bus.. the generator should now charge the batteries and everything not running through the rectifier should be functional.

Dallas
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Sean
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« Reply #9 on: April 20, 2008, 07:43:08 PM »

Well, I didn't want to get into a long discussion about it unless we find out we need to.

A lot depends on what alternator (and/or regulator) you have.  Many here are much more qualified than me to speak about what the stock system on your coach should look like, but there is no guarantee that your system resembles "stock" in any way.

Many coach alternators are externally regulated.  The alternator will have a ground point (usually its own frame), an output terminal (big) where the charge is provided to the batteries, and one or two "field" terminals (smaller) which connect to the regulator.

The regulator, in turn, will have one or two field wires to control the alternator, a ground, an "ignition" lead that tells it to start working, and a "sense" lead that tells it how much voltage is being supplied at the batteries.  The sense lead is usually attached to the same post on the batteries that the large charge cable from the alternator is attached to.

That being said, some alternators are "one-wire" arrangements -- the regulator is internal, and the only sensing of voltage is done right at the alternator.  This type of alternator is either positive- or negative-ground, and can only be changed by opening it up and rewiring it.  Some externally regulated alternators with dual field terminals can be changed from positive- to negative-ground by changing the external regulator and the diode bridge.

I don't know enough about your setup to give more specific guidance here, so let's cross that bridge when we come to it.

BTW, I think it unlikely that your batteries are in backwards.  If they were, and the alternator was working properly, you would have fried something pretty major by now, possibly to include melting the batteries.  (A more likely scenario is that someone did the positive- to negative-ground conversion on the alternator arrangement, but then failed to follow through by changing the gauges and other items to negative-ground models.)  But go ahead and do the test I outlined before you go much further.  And definitely do not reverse the battery polarity yet -- if you have a negative-ground alternator and you positive-ground the batteries, they can blow up, or the terminals can weld themselves in place, or you can fry the alternator and/or regulator.

-Sean
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Dallas
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« Reply #10 on: April 20, 2008, 07:54:50 PM »

Sean,

If it is set up as original, the 53 PD4104 most likely didn't have the alternator. They were still using the dual field generator.
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Stan
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« Reply #11 on: April 21, 2008, 05:43:19 AM »

Dallas has the correct answer on the generator. If you reverse the battery install and don't reverse the generator, you will quickly discharge the batteries and then.charge them backwards. If you have the original generator, it will have a carbon pile regulator which is not polarity sensitive. Most of the gauges will work on either polarity. The only diodes in a 4104 were parts of a selenium rectifier stack used for steering diodes in the alarm system (low oil pressure/high water temperature). If you reverse the battery polarity change these diodes to modern silicon diodes available from Radio Shack (1N4002 or similar).

Positive ground was used by most vehicle manufactures as a cathodic protection system. GM decided that car bodies rusting out quickly was good for business so they went to negative ground. By the early 1950s, GM had such control of the automotive industry, other manufacturers had all changed over to negative ground.
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zubzub
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« Reply #12 on: April 21, 2008, 06:17:23 AM »

Dallas has the correct answer on the generator. If you reverse the battery install and don't reverse the generator, you will quickly discharge the batteries and then.charge them backwards. If you have the original generator, it will have a carbon pile regulator which is not polarity sensitive. Most of the gauges will work on either polarity. The only diodes in a 4104 were parts of a selenium rectifier stack used for steering diodes in the alarm system (low oil pressure/high water temperature). If you reverse the battery polarity change these diodes to modern silicon diodes available from Radio Shack (1N4002 or similar).

 Thank you very helpful from everyone....this is close to my experience....while running the bus with a gas gen charging the batts I was loosing charge (small gas gen with charger)  Everything I have read says that the temp gage won't work reversed.  No big deal as that's an easy switch.  The alarm system is not working anyhow.  This is all good news a sthe gen looks like a recent rebuild so maybe i'll get some life out of it after all.   I'll read up on the pos to neg switch later. 
btw has running this thing for a few hours damaged more han the batts?

Positive ground was used by most vehicle manufactures as a cathodic protection system. GM decided that car bodies rusting out quickly was good for business so they went to negative ground. By the early 1950s, GM had such control of the automotive industry, other manufacturers had all changed over to negative ground.
sounds about right to me, never could see the difference myself (not that I know squat about electonics).  The rust thing mirrors my experience; as a kid I had a friend who's dad worked in design for Chrysler. One of his jobs was engineering those oblong stiffening/weight savings punch outs so that they were positioned to best trap road water = rust.  Nice to know the big boys care so much...
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Sean
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« Reply #13 on: April 21, 2008, 08:09:08 AM »

If it is set up as original, the 53 PD4104 most likely didn't have the alternator. They were still using the dual field generator.


Thanks, Dallas.  I knew someone familiar with this model would jump in.

Is re-flashing the field all it takes to change polarity on one of these generators? (No diode packs, I assume.)

-Sean
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Dallas
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« Reply #14 on: April 21, 2008, 09:00:52 AM »

If it is set up as original, the 53 PD4104 most likely didn't have the alternator. They were still using the dual field generator.


Thanks, Dallas.  I knew someone familiar with this model would jump in.

Is re-flashing the field all it takes to change polarity on one of these generators? (No diode packs, I assume.)

-Sean
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Yes, all you have to do is re-flash the generator field. The regulator doesn't care which direction the electricity is traveling, especially the old carbon pile regulators or the mechanical Delco or Autolite type.

There are some perks to using a generator system as opposed to an alternator... it doesn't care if there is a battery connected or not, no diode trios to mess up, change some brushes and clean up the armature and it'll last a hundred years. You can also weld with the darn things if you are into the McGyver stuff, like I am.

The Dual field generators on the old buses, depending on application had the ability to supply 160A per field.. when the the bus was not using the blowers, or any of the high draw items, only one field was engaged. when you kicked in the blowers for the A/C both fields would kick in to give you 2X 160A, keeping the batteries up and running the blowers from the generator instead of the batteries.

Some of us old fellers do remember the way things use to be done and it still comes in handy from time to time.

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