Batteries not holding charge

[609albert]

 1953  LS 85 Mack,has new 12 volt batteries ,it is not keeping the batteries charged as it should currently has a generator and a rectifier , we are thinking to change over to an alternator, the question is what or how do we address the rectifier connections or are we going in the wrong direction  

[Geoff Weeks]

I suspect you have a Leace Neville alternator with remote rectifier system. It has a remote regulator.

Pictures of everything or replace with a modern unit depending on what you want.

Pictures would be helpful

[Geoff Weeks]

Does it look similar to this:

[CF-Firefighter]

Just a simple observation, I assume that year did not have a battery disconnect? 
 

All of the apparatus I’ve been around in my career, Mack’s have had the kussman “spelling” staple black quarter/half turn battery disconnects. 
 

In the event I’m willing to bet the field is energized or bleeding power  through the generator if nothing else. 

[mowerman]

thats what i was thinking,,,,you gotta draw someplace

[mechohaulic]

On 4/9/2025 at 7:52 PM, 609albert said:

 1953  LS 85 Mack,has new 12 volt batteries ,it is not keeping the batteries charged as it should currently has a generator and a rectifier , we are thinking to change over to an alternator, the question is what or how do we address the rectifier connections or are we going in the wrong direction  

a little bit more info and as requested some pictures help a lot. (1) being firetruck LS 85, is this a hobby truck which sits mostly? (2) new batteries charged fully BEFORE installation?? (3) does it have a master disconnect  and still loosing charge ?  (4) alternator needs power to make power , generator makes it's own :: if I remember correctly. (5) what does the charging circuit show gauge wise when unit running ??

[Joey Mack]

Generators need power, alt. make power...  Mech ???  Your losin it..  🍻. Me too...  

[Geoff Weeks]

47 minutes ago, Joey Mack said:

Generators need power, alt. make power...  Mech ???  Your losin it..  🍻. Me too...  

You got it backwards, mecho had it right.

If this truck has a rectifier, it has an alternator, like the one I posted pictures of. Generators don't have rectifiers (commutator does that job).

[Joseph Cummings]

Are we breaking the 1st law of thermodynamics here?

 

 

Edited Saturday at 04:32 AM by Joseph Cummings

[Geoff Weeks]

9 hours ago, Geoff Weeks said:

 

[Geoff Weeks]

9 hours ago, Geoff Weeks said:

You got it backwards, mecho had it right.

If this truck has a rectifier, it has an alternator, like the one I posted pictures of. Generators don't have rectifiers (commutator does that job).

It has to do with the regulation and how the two connect to the load. Most alternators, with the exception of the early Leece Neville's are always connected to the load through the diodes in the rectifier. Generators and the early L/N have a reverse current relay or "cut-out" that keeps them isolated from the load until the voltage internally is above normal at rest voltage for the system.

Diodes do a fine job of keeping current from flowing from the battery back through the stator windings, but allows any forward current to pass. If there is any kind of load on the output, be it a dead battery or just normal truck loads the stator voltage can't rise above that, and therefore the field current (voltage) can't either. This prevents the alternator from being able to produce useable power unless it has a high enough voltage on its output terminal to begin with.

Generator regulators, (and some of the early L/N alternator ones) keep the generator isolated from the load until output voltage exceed the pull in voltage on the reverse current relay (cut-out), so field current (voltage) will rise and so will the output until it is at operating voltage before being connected to the load. So with these type of regulators, they can start from nothing, build to operating voltage before the load is applied.

It  isn't alternator vs. generator but the regulation and how the load is applied that is the deciding factor.

[Joey Mack]

Ok.  Got it.  I was thinking of gennys needing excitement to generate.  I do know that alts are hooked directly to power.. hot all the time..

[609albert]

yes batteries are new , it has the large disconnect switch  and rectifier 

[Geoff Weeks]

15 minutes ago, 609albert said:

yes batteries are new , it has the large disconnect switch  and rectifier 

You are going to need to be more specific on what you have tested and what you have on the truck.

Does your charging system look like the one in the picture I posted?

Have you checked the regulator?

You can eliminate the system you have now and replace it, or you can address any problems with what is there now.

Both are valid ways to proceed, but a lot depends on your knowledge on working on these systems.

So far you haven't provided much information.

[609albert]

Yes ,It has a Generator, rectifier and voltage regulator mounted on inside of firewall (in cab)

[Geoff Weeks]

Once again, true generators don't use rectifiers, so still trying to get an answer to what you have. L/N calls it a generator because the ultimate output is DC.  The three big studs on the top of the unit are the 3 phase AC output that is fed to the finned rectifier.

SO FOR THE 3rd time, does it look like the one I posted or not. If not we need to see what you have.

Big question is: do you want to keep it period correct or not?

If you are not trying to keep it period correct, then rip everything out and use a modern "one wire" alternator for the correct polarity.

If you are trying to keep it period correct, bushes, brush holders, slip rings, regulators are all still available, the finned rectifier is not, and it would be best to replace with silicon diodes anyway, which will require some fabrication.