What charges a battery, amps or volts? My battery is going weak when driving

[m-mman]

What ACTUALLY charges a battery, amps or volts?

Is it possible to have a charging system with high amps but too low voltage? 

 

The car is a 1942 Hudson. Bless their hearts, Hudson used an unusual design of charging system, I dont think anyone else did this. 

It is a three brush generator with a regulator that adapts VOLTAGE ONLY.   The regulator is a 2 relay design. One cutout relay and a voltage regulator relay. Charging amps is moderated, regulated, adjusted by moving the third brush.  (FYI Hudson used this design until 1950!) 

Because it is a Hudson design it uses its own style of regulator, so parts are not exactly plentiful. 

 

The battery has been going low driving at night with the lights on (sometimes the heater blower too) and the overdrive operating  (an electrical solenoid)  So I dug into it.

 

Testing today (with warm system) I found the following running the engine at 2000 RPM. 

Nothing on = 7.42V  15A  Headlights only 6.33V 30A     Headlights & fan 6.32V  20A

 

Shutting everything off then checking again  7.47V  10A  (could jump to 7.49V  10A)

 

Turning things back on: HL only = 6.24V 30A    HL & fan 6.22V 15A

 

At idle (600 RPM) it shows 6.7V zero amps - I know, generators dont charge at idle. 

 

Specifications from the manual (list a high output and low output generator) either 8V 40A  or 7.8V 29.7A

 

The generator was just rebuilt by a quality knowledgeable shop

The regulator(s) I have tried the one the car came with, and the two NOS ones from eBay. (Again they dont grow on trees)  The regulators are all sealed and the books say that they should never be opened or adjusted. 

 

It looks to me like the amps is within limits BUT the voltage is low. . . . ?

As I understand it the voltage should be adjusted/maintained by the regulator. Voltage is: created by the generator (and could increase to extreme levels) but it is held down and moderated by the regulator. 

 

Any thoughts?

[Joe Cocuzza]

"In summary, while both voltage and current are involved, current is the driving force that actually charges a battery through stimulating chemical reactions. The charger voltage enables the current to flow into the battery by overcoming internal resistance. However, the charging current’s magnitude determines the charging speed and efficiency. So, ultimately, current is responsible for charging the battery itself, while voltage allows the current to act. Managing both is crucial for effective battery charging."

[alsancle]

I think of it this way.  Volts are the size of the pipe.   Amps are how fast the flow is through the pipe.

 

 

[TerryB]

Voltage is the “push” that moves current.  It’s necessary to have enough “push” to overcome the resistance that is keeping the current from flowing.  The charging system has to have a voltage output higher than battery voltage to charge the the battery.  My 1937 dodge truck used the three brush generator and cutout relay.  Adjusting the position of the third brush determined the charging volts.  Too much volts can overcook the water in the battery and ruin it.  The basic three brush systems are always on when the cutout relay is closed and they are unable to adjust generator output as they have no way to sense the amount of charge really needed.  Some better designs included some form of load sensing buy my Dodge did not.

[Bloo]

2 hours ago, m-mman said:

What ACTUALLY charges a battery, amps or volts?

Amps, but it is inexorably tied to voltage and resistance according to Ohms Law.

 

2 hours ago, m-mman said:

The car is a 1942 Hudson. Bless their hearts, Hudson used an unusual design of charging system, I dont think anyone else did this. 

It is a three brush generator with a regulator that adapts VOLTAGE ONLY.   The regulator is a 2 relay design. One cutout relay and a voltage regulator relay.

Lots did it back in the 30s. It is a bit of a mind teaser but not that bad. In practice you were somewhat limited in how big the charging system could be. Not as limited as you are with third-brush-and-a-cutout, but still limited. Almost everyone who was still using this dropped it in 1940 when sealed beams were put on almost all new cars. They were a bit more wattage than the 2330/2331 bulbs that had been pretty common in the late 30s. If I remember correctly, Hudson had some hacks that allowed them to make the system a little bigger. I don't remember what they did.  In 1950 it was decidedly old fashioned.

 

2 hours ago, m-mman said:

Charging amps is moderated, regulated, adjusted by moving the third brush. 

As in any third brush generator. The difference occurs when there is a voltage regulator. On old third-brush-and-a-cutout cars, the rate had to be set low enough to not be boiling the battery all the time. Not true when there is a voltage regulator. The third brush is set in such a way to protect the generator from overcurrent damage. Unless Hudson says differently, it should be set for the maximum current that the generator can take without hurting itself. My 1936 Pontiac has a system like this, as do some late 30s Buicks, and the third brush is not movable.

 

**Importnat note** Many third brush generators have a test current listed in the service manual that is for quick bench testing only, to prove function. If you see that, don't confuse it with what the generator can take all day long.

 

On a system with a voltage regulator, current regulation, in this case done by third brush, is only there to protect the generator. A generator, unlike an alternator, will happily charge higher than designed until it melts. If Hudson left that brush adjustable after they added a voltage regulator, they have to have told you how to set it correctly. I would expect it to be a default value that you set on the bench while loaded and never change. Read carefully to make sure you are setting it to the value it is intended to run at, not a test setting only intended to prove bad/good generator.

 

2 hours ago, m-mman said:

Because it is a Hudson design it uses its own style of regulator, so parts are not exactly plentiful. 

Unless it has been on fire or something, it can probably be cleaned and set up.

 

2 hours ago, m-mman said:

Testing today (with warm system) I found the following running the engine at 2000 RPM. 

Nothing on = 7.42V  15A  Headlights only 6.33V 30A     Headlights & fan 6.32V  20A

 

Shutting everything off then checking again  7.47V  10A  (could jump to 7.49V  10A

How are you testing amps? I think that's too high, and anyway it is not tracking in a predictable way. Ignoring the amps measured, the voltage regulator setting sounds fine. We expect 7.4 volts on nice big systems, 7.5 volts on most cars, and and 7.6 volts on old systems that are tiny (like my Pontiac). There are exceptions. Always believe the manual. It sounds like the generator is not able to supply enough amps. It may need work, or if the third brush is adjustable, it may be too low.

 

2 hours ago, m-mman said:

Specifications from the manual (list a high output and low output generator) either 8V 40A  or 7.8V 29.7A

Those are the test specs, because they are at voltages higher than you would ever allow on a voltage regulated system. And now you get into the first screwball idiosyncrasy of third brush. If the voltage is allowed to rise above normal, the maximum available current will also rise.

 

The second screwball idiosyncrasy of third brush, closely related to the first even though it isn't obvious, is that available current vs RPM runs in a bell curve. In other words, above idle the generator starts charging, but does not have full current available. as RPM rises, the available current rises until it gets to some magic RPM, and then it starts falling off as the RPM continues to rise. Remember the whole point of currrent regulation on a voltage regulated car is to prevent overcurrent damage to the generator, so the brush has to be set to limit at the highest point. That's the main reason everyone else abandoned third brush. If you use a 40 amp current regulator (pulling a random number out of the air) and a two brush generator, 40 amps is 40 amps, and all of it is available as long as the generator is turning fast enough to do it. Of course if it isn't turning fast enough, less is available.

 

In a perfect world, a voltage regulated generator would behave exactly like an alternator, except for having less charge at idle. Post 1939, most of them do within reason, if not loaded up with a bunch of Trippe Lights or whatever. Assuming a fully charged battery (important), and engine running above idle, the system voltage is the voltage regulator voltage, and on most cars we expect about 7.5V at room temperature. The temperature matters if you are setting it.

 

When the battery is charged and the system is keeping up with the current (Amps) demand, the voltage should remain about the same, 7.5 volts or so, with the voltage regulator happily buzzing away keeping it from rising.

 

When current demand (Amps) by the ignition, lights, heater, radio, and whatever else exceeds the maximum current available, the battery suddenly becomes the source of current. The natural voltage of the battery is 6.3 volts. The system voltage will drop fairly suddenly to around 6.3 volts, and go down from there as the battery discharges. When some demand goes away, and the generator can keep up again, it should go back up fairly quickly, as it will on a modern car, or most post 1939 cars as long as they aren't loaded up with accessories. If the charging system is too small though, you might spend a lot of time with the voltage low. If there is only two amps of capability left over after lights and accessories to charge the battery (pulling numbers out of the air again), and it has to charge the battery with that, that is going to take a while just like a trickle charger would, but when the battery gets back to full charge you'll be back up to 7.5 volts or so.

 

i'd like to know how you got those amp readings. They aren't making any sense to me. It would be interesting to know how much current the heater and the overdrive solenoid draw. The lights can probably be figured out online (6006 headlight bulbs?).

 

My first reaction is that the generator output is low and the regulator is fine (once again ignoring the amp measurements). Unfortunately engine speed is going to affect how much current is available, so it is really hard to predict.

 

EDIT: I can't help but wonder if your regulator or generator might not be grounded good.

 

Edited February 15 by Bloo (see edit history)

[joe_padavano]

Think of it this way. Voltage is PSI. Amps is gallons per minute. You need both to feed your carburetor.

[m-mman]

A charging system that can keep up with the ignition only is great. However a charging system that has to borrow from the battery when the lights, OD and heater is on isn’t going to take you very far.  
 

I know that the battery is getting weak when it doesn’t shift into OD.  (The lights are probably dim also but in the city with the high intensity search lights on modern cars how would you know?). 
 

So driving all DAY is nice but it’s winter and there’s still a lot of darkness in the day.  
 

Looking at the numbers I’m thinking that while the amps seem good a low voltage is preventing a “charge” or replacement for the operating current. (Lights and OD) 

 

I’m seeing the voltage drop to 6.2 - 6.3 and I’m thinking that isn’t enough to force the electrons back into the battery so they are stolen from it.  

Shouldn’t the system show 7.1 - 7.2 volts at 40-50mph? 
And shouldn’t this target voltage be set/created by the regulator?

So maybe it needs adjusting?  
 

The amp gauge I’m using is an old Stewart Warner under dash unit. (0 to 60 amp scale). It’s the only amp gauge I could find that could readily measure 35-40 amps. It’s working well. 
 

Another test, I grounded the field and saw 8.55 volts and 50 amps.  So I think the generator can put out what I need, but is it still the regulator that is holding things back? 

[Bloo]

These amp readings are coming from a dash ammeter in the car? If so ignore them for now. Double check that the generator and regulator are grounded well and together. If one is grounded to the engine and the other is grounded to the body, verify the body and engine re well grounded together.

 

Now about the car's ammeter... All accessories must be connected to the generator side of it. Lights, radio, heater, wipers if electric, whatever. It all goes on the generator side, NOT the battery side.

 

An exception might be the horn. GM puts the horn on the wrong side, and i have a theory why, but that's not important right now. Hudson might have done the same, I don't know, but it only draws current when you honk so it wouldn't matter.

 

Current drawn by anything that is on the wrong side of the ammeter will register as charge. It sounds like that might be happening. If so, it is an illusion.

 

The ammeter in the dash should only show current in or out of the battery. That way when the system keeps up, or is at least gaining, it will register charge. When they system does not keep up, it will register discharge.

 

1 hour ago, m-mman said:

Shouldn’t the system show 7.1 - 7.2 volts at 40-50mph? 

Maybe. Probably. As long as there is enough current available to keep up, yes. It's third brush, so the available current will drop at higher speeds.

 

1 hour ago, m-mman said:

I’m seeing the voltage drop to 6.2 - 6.3 and I’m thinking that isn’t enough to force the electrons back into the battery so they are stolen from it.

That's true, but don't allow it to mislead you. It is precisely what happens when there is not enough current available.

 

1 hour ago, m-mman said:

And shouldn’t this target voltage be set/created by the regulator?

Yes.

1 hour ago, m-mman said:

So maybe it needs adjusting?

Probably not. It was at 7.47-7.49 unloaded, and that is *exactly* where I would expect it to be set, at least without a manual to look at. It won't be far from that. If it was set at 6.3 it never would have got there.

 

 

1 hour ago, m-mman said:

 

Another test, I grounded the field and saw 8.55 volts and 50 amps.  So I think the generator can put out what I need,

In that case, there must be a resistor in the regulator from the field to ground. The opposite end of the field is powered by the third brush. The regulator points short out the resistor to kick the field on high and the generator into high charge, The regulator relay coil is powered by system voltage. when it gets to 7.5, the points open, the voltage drops, points close, voltage at 7.5, repeat, repeat, etc. It is probably designed to rattle fast or buzz so you notice it less in the headlights.

 

Note that the "sense" point for system voltage is at the regulator, power and ground as it exists in the regulator. The ground that turns the field on is also at the regulator. I think you have stray resistance somewhere between the generator and the regulator. Probably in the ground(s).

 

One unrelated thing, just in case you don't know. never run a third brush system with the battery disconnected. They burn the field up if you do.

 

Edited February 16 by Bloo (see edit history)

[roysboystoys]

My experience with Hudson's with that set up is, If the Overdrive doesn't work when the lights and accessories are on and the voltage in range, always boiled down to a bad battery. I believe you will find a higher amperage battery is specked for a car with overdrive, or 8 cyl.

I've run into this on several of my own Hudson's, and a fleet of them I maintained for a collector.

You can mount the later style generator and voltage regulator and rewire the regulator circuit to work.

I believe the later regulator was used as a replacement from the factory, with a bulletin to show how to make it work. The brain is a little foggy on the details.

I've had several cars with both systems, both worked well , with a heavy duty battery.

 

[m-mman]

Additional grounds and possible battery. Both excellent ideas.  Now I can get to work.  
 

FYI I’m currently using an Optima battery.  

[Steve Braverman]

[dodge28]

I your battery is in poor condition there is no amount of  repair and adjustment is going to help. Do a load tests. Poor grounds will affect charging.

[m-mman]

A lot of folks have posted good information about electrical theory.  
 

In my case I am seeing good flow (amps) with low pressure (volts). In discussing theory

 

 

would a six volt battery charge if the system provided say 20 amps but at 4 volts?  

 

By comparison, 100 gallons a minute through a big pipe at 1-2 psi isn’t going to produce much of a dribble from a faucet that is 3 feet above the big pipe despite the river that is flowing through the pipe. 

[TerryB]

Charging volts has to be higher than battery voltage.  On newer cars the amp gauge was replaced with a voltage gauge because the charging system voltage is the parameter you want to know and I think people understand voltage better than amps.

[dodge28]

In a perfect functioning system as voltage rises amp drops. For this reason most modern vehicles instrument gauges only have voltmeters  . In the old cars the distribution load starts from a Amp meter. I have never seen and old car with a volt meter. I am not saying there is not. 

[Bloo]

57 minutes ago, m-mman said:

 

would a six volt battery charge if the system provided say 20 amps but at 4 volts?  

No. The battery would try to charge the generator or charger. Current will flow from the highest voltage source.

 

I think you may be approaching this wrong. Volts, Amps, and Ohms are inexorably tied by Ohms law. It is a natural law you can't change. As a result of this, pushing 20 amps at 4 volts into a 6 volt battery is literally impossible if the battery has any charge in it at all.

 

The thing about Ohms Law is is that if you know two of the three at any one device (like a hot running headlight bulb for instance), you can just calculate the third. Volts=Amps x Ohms. If you change one, the others have to follow. You can't get around it. If I lower the Volts at a hot headlight bulb, the Ohms wont change very much as long as the filament stays hot, so the current (Amps) has to go down when I lower the voltage.

 

Charging a battery is a funny thing though. In a car, with a sophisticated charging system like a 2-brush generator with a 3 unit regulator, or an alternator, the strategy is to have more current available from the charging system than you will use.

 

Current only flows on demand. Demand made by lowered resistance in devices. If you have a charging system that can provide 50 amps, and the ignition and lights (or whatever) that you have running draw a total of 10 amps, that leaves 40 amps available to charge the battery. The battery won't ask for all 40 or anything near that.

 

Back to charging the battery. If you regulate the system to a specific "magic" voltage, usually 7.5-ish at room temperature in a 6 volt car, a dead battery will draw very little at first, more as it gets charged. If this "system voltage" is what it should be, the battery will self regulate and stay fully charged. If the system voltage is too high, the battery will always be somewhat overcharged. if it is too low, always undercharged. Tenths of a volt matter. Once full the battery will draw very little current, and can be fine at 7.5V all day long. Well almost. I guess if you drive all day the voltage might rise a little bit above expected. Some cars have an extra contact point in the voltage regulator relay to shut the system off intermittently if this happens. Most others ignore it.

 

So... back to your Hudson. You do have separate control for both voltage (the regulator) and current (the third brush), but you can't use and set them that way because you can't fool mother nature. Current to power accessories is drawn off first from the generator, and whatever is left is available to charge the battery, but only if the battery asks by drawing current. How much is up to the battery.

 

If the total load of accessories, plus what the battery wants to recharge itself exceeds what the generator can put out, the voltage drops. Unchecked, it will drop from about 7.5 to about 6.3. The thing is though, when the voltage drops below 7.5, the voltage regulator relay should react. It is just a relay that opens points at 7.5 volts. It seems to be regulating at 7.5 volts when there is hardly any load. When it drops below 7.5 volts, the voltage regulator points close. That shorts the field terminal on the generator to ground. Why cant it do that? When you did that, it charged like crazy.

 

The most likely thing in my opinion is when voltage falls below 7.5, and those points close and ground the field wire to the regulator frame, the regulator frame must not be grounded to the generator frame. Otherwise it would have the same effect you got by grounding the field. Then the voltage should go too high like you saw (8+ volts?), which would close the points, raising the voltage, opening the points again, etc. The relay probably buzzes and since the battery itself reacts much slower than this buzzing relay, the system stays at a stable 7.5 volts.

 

 

Edited February 16 by Bloo (see edit history)

[m-mman]

Good explanation.  Thanks.  
 

Sadly I can’t try out the suggestions until next week.  I’m taking a short excursion this weekend with a friend.  I had hoped to use the Hudson but I have to take the (modern) 1966 Mercury instead.  

Edited February 16 by m-mman (see edit history)

[Larry Schramm]

On 2/15/2024 at 4:23 PM, alsancle said:

I think of it this way.  Volts are the size of the pipe.   Amps are how fast the flow is through the pipe.

 

 

 

Actually the other way around.  Amps is the amount of current or electrons that can go through a wire ("or pipe").  The amount of electrons/amps is governed by the size of the wire. 

 

Volts is the amount of "pressure"  or push that is exerted on the available current.  No different than water in a hose.  More pressure/volts can accomplish more water/amps through a given size of pipe/wire.

Edited February 17 by Larry Schramm (see edit history)

[Frank DuVal]

On 2/15/2024 at 4:23 PM, alsancle said:

I think of it this way.  Volts are the size of the pipe.   Amps are how fast the flow is through the pipe.

See Steve's picture. Ohms is the size of the pipe. Inversely that is. Larger pipe fewer ohms (resistance).

 

I have that picture posted at work to explain ohms law!

[m-mman]

Ok, it has been a while but I made some changes and have updates to report. 

 

When I full fielded the generator (grounding the field wire) I got 8.55 to 8.63 Volts and 50 amps. So the generator should be Ok. 

 

Bloo theorized that since I was getting such good numbers with a full field test, then perhaps the problem is with the ground and that I should run a solid connection between the generator and the regulator. Good thought, makes sense. 

I did, then the rains came (in CA) and life happened, so I didnt get back to it for a while. 

 

With a recent clear day and twilight hours (so I would use my headlights) I took it 30+ minutes to dinner and 30 minutes back. Ran up there just fine. Upon return after 25 minutes of driving, the OD quit. I have come to learn that this means that it is not charging. (Note: the charge light remains off)  We were only 10 minutes from home so there was no problem making it back. 

 

In the garage I checked again and I was getting only 6.55 volts total at about 2000 RPM. I full fielded it again and saw the same 6.55 - 6.56 volts. 

I had 6.46 volts at idle. Headlights on I was getting 6.24 volts then switching them off I saw 6.13 volts. (Again this was after 30-40 minutes of operation) 

 

Again I am thinking that for WHATEVER REASON the system is not able to put out enough VOLTAGE to overcome the electrical demands and charge the battery. 

The charge light never came on (it is working) which implies that there are AMPS flowing. 

 

In testing and working with it, it seems to provide the higher necessary VOLTAGE when it is cold. (Starting in the morning) and the low/no charge situation happens after it has been driven for a while. 

 

I like the 6 volt system, and l like originality but this is frustrating. 

Hudson changed their charging system in 1951. PERHAPS acquiring parts and making it a later design would work?

I do not like when people change to (6V) alternators, but this thing is putting those ideas in my head.  <arrrgggg>

 

[Fordy]

It sounds to me like there is a problem within the insulation of the windings. This is essentially varnish and I would bet it is breaking down with the heat of the motor. Not exactly causing a short but reducing dielectric strength of the varnish. This is also made worse by any gunk that may be in there too. Only sure fix if that is the case would be a full rewind of both the fields and armature.

Steve

[Larry Schramm]

6.55 volts is basically battery voltage and the generator is not charging.  A suggestion might be to take the generator to a generator repair shop and have them check it out for you.  They should be able to inspect it and probably load the generator to see what it is capable.

 

I recently took an electric motor (a generator in reverse) to the repair shop and the guy looked at it and told me almost immediately that the wiring looked good and probably needed just a good cleaning and maybe a bearing or two.  His inspection and evaluation was worth what I am paying him for his expertise.

Edited March 16 by Larry Schramm (see edit history)

[Bloo]

4 hours ago, m-mman said:

In the garage I checked again and I was getting only 6.55 volts total at about 2000 RPM. I full fielded it again and saw the same 6.55 - 6.56 volts. 

I had 6.46 volts at idle. Headlights on I was getting 6.24 volts then switching them off I saw 6.13 volts. (Again this was after 30-40 minutes of operation) 

So you full fielded it while it was having trouble, and it didn't even try to come up to 7+ volts? Even with the lights off? And its a 50 amp generator?!

 

I think @Fordy and @Larry Schramm are on to something here. There is little doubt that you have a problem in the generator. If you full field it, it should try to come up, period. Full fielding makes it do everything it can. If it was a 15 amp generator or something like that, and the battery was low, the response might be slow, but 50 amps?! That should jump up immeidiately. I'd be looking at everything under a magnifier, and testing the windings in every way I could think of before committing to a rewind though.

 

Only exceptions I can think of:

 

1) If that 6.55 volts was taken at the battery, and not the generator, and the generator DID go high when you full fielded it, then there is high resistance in the wiring, or the ground, or the cutout points in the regulator.

 

2) On my trip in the 36 Pontiac from WA to WI, I discovered the generator stopped working after about 45min(?) or so on the road. Full fielding didn't help. I was convinced there was a broken wire in the generator somewhere. When I got home I tore the generator down and scrutinized it closer than any generator I ever worked on and found nothing wrong. It turns out that the radiator overflow tube was supposed to have about a 4 inch piece of hose on the bottom to make it exit below the side shields, and it wasn't there. The copper tube ended right in front of the generator pulley. After about 45 minutes or so on the road, apparently the radiator would dribble a few drops of antifreeze on the belt and pulley and it would slip. It wasn't enough that you could see anything wet, nor did it squeal, or do anything else to tip me off that it might be a belt problem. One day I caught it dribbling a few drops. I shut the engine off and found I could spin the generator pulley easy. This had evidently been wrong the whole time I owned the car, and I never noticed it on shorter trips. Four inches of hose fixed it.

 

 

Edited March 16 by Bloo (see edit history)

[leomara]

I recently had an odd experience with my 1991 Ford Bronco.  Battery discharged, took the battery to the local NAPA store where they checked it and said it was good, just needed a charge.  Charged it and within 5 days it was discharged again.  I start thinking about parasitic drains and have my mechanic check that out and he finds nothing but recommends that I replace the battery even though it was only 2 1/2 years old.  Go to NAPA and get another battery, put it in and in 5 days it's stone dead.  Go back to NAPA and they charge it for me but recommend that I leave it there overnight so they can see it it retained the charge.  The next day they said they did not like what they saw and replaced that battery with another.  Since then, no problems.  Conclusion, batteries that are no good can take a charge and not retain it, even new ones.  Go figure.....

[Larry Schramm]

One thing that I learned years ago was aftermarket anything.  That includes radios. 

 

I had a vehicle that if I did not drive it every day the battery would go dead.  I checked the parasitic drain from the radio and found that it was HUGE. Poor design to keep the radio memory and clock alive. 

 

Changed out the radio and never had another problem.