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Boost generator output voltage for AGM charging

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My 110 has a No.16 Mk.1 Generator, said to provide 28V, 90A.


I've fitted two Banner AGM batteries, which like to be charged at 14.8V each, AGM's require a higher voltage compared to Lead Acid.


[i'm assuming that I can just divide the 28V by 2 to get the voltage that each individual battery is charged with, not sure if that's correct]


I see a few options and possible problems..


Can I modify the generator so it will output a higher voltage?

But 24V equipment might be put on a higher strain by this perhaps, or does the battery in the circuit smooth this voltage difference out?


I was thinking about an LDO between generator and battery, but don't think they come in versions that can handle a 100A.


Perhaps any other idea's or input?




Edited by SjoerdV
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Sjoerd I believe this alternator uses the Prestolite regulator 600-9. There seems to be no setting that you can change on this to adjust the output.


However if you look at the circuit diagram below you will see it has a diode trio for the vehicle batteries & another diode trio for the radio batteries. It seems that you might be able to use one output that could be regulated down to the chosen charging voltage for one of your batteries & do the same again for the other battery.


Is your 110 exclusively 24v? Or is the automotive side 12v & the radio batteries 24v? I don't know how the outputs are configured in the military version of this alternator whether there are two independent outputs or whether they are combined in parallel. But it might be possible to tease out two independent outputs?



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Hi Clive,


Thanks for that link, that will go into my car documentation :). Is there any way for me to verify that this regulator is actually fitted. It must be inside of the device, as there is no external box.


The alternator has the B1+ wired to the batteries (via the starter).

The B2+ was originally probably used for the radio's, but is now disconnected.

The WL is connected to the warning light (battery icon).





The vehicle is 24V, with the exception of the headunit and windshield heater, currently this is hooked up to a 24 to 12V converter. Remainder of the vehicle is fully on 24V.


You say regulating down, but I assume you mean up, as I'm trying to supply a higher voltage to the batteries.


So, if adjusting the regulator is not an option, then perhaps add a voltage step-up/boost between the starter and batteries? Can this be done efficiently?


Thanks Clive! (and yes, I read All Charged Up :angel:)

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Actually now I have thought about it a bit more, what I suggested is not a very good idea because the output negative rail is shared & then there is the issue that the "upper" battery has a negative that is 12v+ above earth.


Yes the regulator is internal. I used to have a 12v vehicle that I needed a 24v supply for radios. I connected the radios to an additional 12v battery with its negative going to the positive of the vehicle battery. To charge the upper battery I used a 12v inverter that gave a completely isolated supply so there were no earth clashes.


The AESP Technical Description that I have should cover that alternator is an early edition, unfortunately that particular chapter is marked as "not yet published".

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They may be perfectly OK with the existing setup. The standard radio battery was the UK6TN (4 of them to give 24 volts nominal), and the radio kit of the period used a voltage control relay to allow it to be operated with the alternator charging the batteries. The average alternator output may well say it's 28 volts, but it's rectified AC (3 phase, I think), so the peak voltage will be higher than that.


The UK6TN batteries were replaced by the UK6TNMF which is an advanced glass mat type (as far as I'm aware), and should be a 'drop-in' (not on your foot) replacement.


I'd be very wary about trying to increase the alternator output voltage. The whole system was designed to operate on 24 to 28 volts, and an overvoltage would not do the electronic equipment any good at all.



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The car isn't running currently, should run in a few weeks. What I'll do is actually measure the output voltage over the range of a small drive.


The UK6TNMF is rated to charge at 14.4V (which would be 28.8V for a 24V-setup), a slightly lower charging voltage.


I'll revisit the topic in a few weeks :D

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