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Generators & Electric Motors General Discussion Antique Generators and Old Electric Motors: Questions and answers about restoring and showing old power generation systems.

Generators & Electric Motors General Discussion

Regulating a 32v dc generator


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  #1  
Old 09-02-2014, 05:51:03 AM
Pettergen Pettergen is offline
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Default Regulating a 32v dc generator

Hi guys,

I've picked up an engine and Davey 32v dc generator set. I believe that the generators were originally connected to lighting plant switchboards, and part of that was a resistor as they were also able to recharge battery banks when knife switches were changed.

I'm looking for some advice on how to regulate the generator to charge my 12v battery bank and not exceed the maximum 40 amp rating.

Cheers
Chris
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  #2  
Old 09-02-2014, 06:17:12 AM
armandh armandh is offline
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Default Re: Regulating a 32v dc generator

how is the generator field wound?

shunt, series, both?

mostly one would be dealing with the shunt winding

adding fixed resistors in series with shunt circuit would bring the voltage down

this will not be very efficient with 1/3 the voltage out [more or less]
and the same current limit you will only get 1/3 the power

unless you charge the batteries in groups of 3 in series [or 2 for 2/3]

what is the end use? lighting ? why not 32 or 24 volt?

Last edited by armandh; 09-02-2014 at 06:38:30 AM.
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  #3  
Old 09-02-2014, 07:23:13 AM
DeereWrench DeereWrench is offline
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Default Re: Regulating a 32v dc generator

Hi I also have a F&J 32 volt generator. Can I use two 12 volt an a 6 volt in series to get close to 32 volt. As it has a 32 volt coil to run on an start with the generator. Thanks Mark
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Old 09-02-2014, 08:04:07 AM
Pettergen Pettergen is offline
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Default Re: Regulating a 32v dc generator

Quote:
Originally Posted by armandh View Post
how is the generator field wound?

shunt, series, both?

mostly one would be dealing with the shunt winding

adding fixed resistors in series with shunt circuit would bring the voltage down

this will not be very efficient with 1/3 the voltage out [more or less]
and the same current limit you will only get 1/3 the power

unless you charge the batteries in groups of 3 in series [or 2 for 2/3]

what is the end use? lighting ? why not 32 or 24 volt?
Hi,

It from memory is shunt wound.

The battery bank is 12v, because that's what I had. I can configure them for charging at 24v easily, but my main concern is to protect the generator from being overloaded.

I have 32v light globes that I can use, but wanted to make use of it for charging as well. I just don't know the best way to regulate/limit the current when charging.
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Old 09-02-2014, 08:04:49 AM
oldgoat oldgoat is offline
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Default Re: Regulating a 32v dc generator

I'm pretty sure Davey lighting plant generators only used shunt fields in them so a variable resistor in series with the field would do the job. The value would be low from memory it was about 10 ohms.
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Old 09-02-2014, 08:09:12 AM
Pettergen Pettergen is offline
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Default Re: Regulating a 32v dc generator

Thanks. It is currently wired directly to a power point so I'd have to try and identify the wiring. I've seen an old lighting switchboard with a dial knob, presumably a potentiometer or similar?
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Old 09-02-2014, 09:15:13 AM
cornbinder89 cornbinder89 is offline
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Default Re: Regulating a 32v dc generator

four 8 volt in series were common on 32 volt systems. I agree that knocking the voltage down to a 12 volt system is going to really reduce the power (watts) avaiable. How is the field fed?
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Old 09-02-2014, 12:37:49 PM
Andrew Mackey Andrew Mackey is offline
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Default Re: Regulating a 32v dc generator

Deerewrench, you might get away with 30 volts for a short time, but you will be overcharging your battery set, which will shorten service life. You might try 3 12 volt batteries, as your plant should actually put out 37.5 VDC if it is a charging unit (the overvoltage takes up internal losses in the batteries. If you do not already have batteries, your best bet is to pick up 4 8 volt batteries, I think still available from tractor supply or a good battery shop. If your unit only puts out 32 volts, then like I said, the 30 volts will work a while.
Andrew
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Old 09-02-2014, 04:24:56 PM
Thaumaturge Thaumaturge is offline
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Default Re: Regulating a 32v dc generator

Series two of these, use them to charge two isolated banks. With added heat sinking (100W default) each module can handle up to 200 W. Setable voltage, high conversion efficiency and current limit. Dirt cheap. Sadly max input is 30V, but will take much less. 18V each when connected in series will still properly regulate to charge 12V batteries. (13.5)
http://www.dx.com/p/adjustable-step-...-dc-12a-242230
Doc
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Old 09-02-2014, 06:38:20 PM
Thaumaturge Thaumaturge is offline
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Default Re: Regulating a 32v dc generator

Forgot to add using two large electrolytic caps stacked in series as a voltage devider to define mid connection point between series modules. Basically just put a large cap across each input when you series them.
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Old 09-04-2014, 06:18:14 AM
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BMiller BMiller is offline
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Default Re: Regulating a 32v dc generator

Caps to balance the line on DC? It works on AC, but not DC. You'd need resistors instead

Bill Miller
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Old 09-04-2014, 09:22:32 AM
armandh armandh is offline
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Default Re: Regulating a 32v dc generator

to charge 12 volt I suggest using lower engine speed for the lower voltage

with an amp meter and a large diode or cut out relay, bring the speed up to the desired charge rate or generator current limit.
a current relay to kill the engine when the low charging rate indicates done might be a nice addition
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Old 09-04-2014, 04:34:52 PM
Thaumaturge Thaumaturge is offline
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Default Re: Regulating a 32v dc generator

Quote:
Originally Posted by BMiller View Post
Caps to balance the line on DC? It works on AC, but not DC. You'd need resistors instead
Bill Miller
Caps WILL do the same, but without constant heat (power) loss.
Doc

Quote:
Originally Posted by armandh View Post
to charge 12 volt I suggest using lower engine speed for the lower voltage
With significant total power loss, but that would work.
Doc
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Old 09-05-2014, 05:55:13 AM
armandh armandh is offline
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Default Re: Regulating a 32v dc generator

Quote:
Originally Posted by Thaumaturge View Post
With significant total power loss, but that would work.
Doc
sure but they would get a lot of power loss any way
same current @ 1/3 the voltage = 1/3 the watts
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Old 09-05-2014, 04:17:10 PM
Thaumaturge Thaumaturge is offline
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Default Re: Regulating a 32v dc generator

Quote:
Originally Posted by armandh View Post
sure but they would get a lot of power loss any way
Not so using two high efficiency switcher supplies in series. Those I suggested do 92% efficiency.
Doc
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Old 09-07-2014, 09:12:05 PM
electronics sam electronics sam is offline
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Default Re: Regulating a 32v dc generator

Quote:
Originally Posted by deerewrench View Post
Hi I also have a F&J 32 volt generator. Can I use two 12 volt an a 6 volt in series to get close to 32 volt. As it has a 32 volt coil to run on an start with the generator. Thanks Mark
I believe that you will have unequal charging due to unequal plate area (amp hr) between the 6V and 12V batteries. You would need to equalize the charging currents so the 6V and 12V received the proper currents (usually defined nominally as C/10 as I recall) without overheating, gassing, or boiling away. Also remember, that you usually have to have a higher charging voltage to create the current to drive the chemical action of the lead acid, so all things being equal, 32V may not be enough to fully drive the charging action for a 30V set of batteries.
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Old 09-07-2014, 09:36:36 PM
Pettergen Pettergen is offline
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Default Re: Regulating a 32v dc generator

This has all been very interesting reading. I was thinking about lowering the speed and connecting batteries up as 24v banks. This will show my electrical ignorance, but how do I ensure (using the simplest and readily available methods) that I don't exceed the 25a rating of the generator?
I believe the original switchboards used a wire wound resistor (dial) and monitored charging by the built in ammeter and volt meters.

I like old school, so don't need anything fancy... Unfortunately I don't have the original switchboard that went with this all....

The engine won't be left unattended, so I'm happy to monitor things...

Cheers
Chris

Duh... I just read an earlier post I missed...

So limiting the engine speed and therefore generator, I limit the voltage and current.
Correct?

Cheers
Chris
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Old 09-07-2014, 10:28:09 PM
Radiomike Radiomike is offline
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Default Re: Regulating a 32v dc generator

Lowering the speed will reduce the power output. You will still need a variable resistor in series with the shunt field to regulate the voltage and hence the current. A discharged battery will present a low resistance to the dynamo so the voltage will need to be regulated. I suggest you purchase an inexpensive DC ammeter, reading say 30 Amps. Be aware that some ammeters need an external shunt.

Provided the batteries are similar in terms of amp/hour capacity they should charge well in series. To charge a 30 volt system up to 36 volts may be needed, 2.4 Volts per cell. A good voltmeter is also a good idea. If they are flooded batteries an hygrometer is a wise investment, if you can access the electrolyte. Batteries need current passed through them to effect the chemical changes as part of the charge regime.

This link explains some of the basics of charging lead-acid batteries.
http://www.evdl.org/pages/hartcharge.html

Mike
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  #19  
Old 09-08-2014, 12:05:59 AM
Pettergen Pettergen is offline
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Default Re: Regulating a 32v dc generator

Thanks Mike,

I have most of those recommendations already covered with ammeter etc in my shed.
Do you have any recommendations for a resistor capable of the amperage we're talking about? I had a quick look at a local electronics suppliers and most seems to be much lower amp ratings..

Cheers
Chris
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Old 09-08-2014, 08:00:55 AM
Pettergen Pettergen is offline
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Default Re: Regulating a 32v dc generator

By the way, is anyone familiar with the wiring of these units? I've attached a shot of mine.
The two red wires together go to a power outlet as + & - .
I'm guessing the green is the shunt field and the jumper red is energizing it?
Yellow I have no idea? Can anyone add any insight?
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