How do I keep the generator from exceeding over 48 volts

Thread Starter

Kevin Nguyen 3

Joined Oct 25, 2016
I'm trying to use this generator to recharge my hybrid go kart while we are running on gas power. However, we are afraid the generator will generate too much energy and destroy our batteries (4 batteries combined to store 48V). Is there any way to prevent this? Please help, in great detail if possible please (very little experience in this type of thing).

Here's the link to the generator:


Joined Mar 30, 2015
Welcome to AAC!

It's generally not a good idea to charge batteries in series. A weak battery won't charge completely and will eventually fail. If it fails short, it will subject the other batteries to higher than expected charging voltages; resulting in their failure. Not to mention that battery run time will be decreased and the good batteries will abuse the weak one.

If you decide to do this in spite of that, you'll need a voltage higher than the nominal voltage to charge them.

What are the specs for the generator? Does it have any built-in over voltage protection?


Joined Sep 17, 2013
The generator in the link is a permanent magnet type, so the only way of reducing its output voltage is to reduce the rotation speed or else draw enough current from it (possibly using a dummy load) that the generator's internal resistance drops the necessary voltage.

schmitt trigger

Joined Jul 12, 2010
As Alec correctly mentions, without field control the voltage will rise directly proportional to RPM.

You could do a brute force approach like Alec mentions, but without its Kw rating we don't know how much power this could draw from your gas engine, reducing effective HP.

A better, but more complex solution, would be to add a SMPS regulator on its output.


Joined Nov 4, 2013
To give you any real definitive answer wee need to know the type and size of your battery bank.

As for the not charging in series thing if the batteries are all brand new and of identical size its not rally a valid issue or concern being thee are millions of devices in the world that run far more and four batteries in series without a problem.
After all, a 12 volt battery is just six 2 volt cells in series and 48 volt is just 24 of those same cells in series.

As for the 48 volt alternator I would not waste money on the one yo have linked too. You can turn a common commercial 24 volt high output unit into a 48 volt unit very easily if you have any degree of electronics skills.

Pretty much any of the big 24 volt 100+ amp commercial units like the big Delco, Prestolite and Leece Neville units (my favorites to modify and only ~$200 - $250 new) have multiple windings in parallel inside their stators most often set up in a three phase delta configuration. By reconfiguring them to a Wye connection they will easily produce 48+ volts and if the sets of parallel windings for each phase or put in series they will easily do 200+ volts DC without problems.

The only real issue is the rotor is still 24 volt so you need to either add a DC -DC buck converter to supply it and the regulator with 24 volts or use a properly sized and fairly large resistor. that and the stock 24 volt regulator will need a simple two resistor voltage divider on its sensing input so that it will see the new output voltage as still being the stock 24 volt it's looking for.

Still, a stock 24 volt 100 amp alternator can be converted over to work as a 48 volt 50+ amp unit with minimal work and modification.


Joined Mar 30, 2015
After all, a 12 volt battery is just six 2 volt cells in series and 48 volt is just 24 of those same cells in series.
And when my car battery craps out, it's usually because one cell is bad. More cells decreases reliability. One weak cell will decrease battery performance and the stronger cells will abuse the weak one; accelerating it's demise.


Joined Nov 4, 2013
More cells decreases reliability.
Sort of but the reality is no one wants to use single cell units in most any application unless the sheer size of them dictates that it's the most practical way to physically work with them.
Basically, ideal operation Vs realistic application says that putting many cells in series into one package is what is most practical method to deal with them in normal applications.

As far as when a a battery has a cell go bad in the vast majority of cases the rest are pretty close behind it being they all have seen the exact same service conditions and life.
I've worked around enough industrial backup batteries that had taps for equalizing or isolating individual cells to know when one cell goes bad in a battery the others don't have much service life left in them either.

Same with common power cells in everything else. When a cell goes bad in my cordless tool battery packs the rest of them are not far behind either.
Believe me I've tried taking the remaining still functional cells from battery packs and putting them together to make another good battery from them and the reality ws that the ones that were still working were very near their end of life anyway.

Same with the service life of a battery in general no matter how well you treat them in the end they are still a consumable that eventually wears out breaks down and fails. It's just how it works.
It may not provide ideal cell or battery life but it sure a whole lot easier to work with and for most people convenience is what matters.

I don't measure the value and function of any of my battery powered devices by how long the battery service life is. The only thing I care about is how well do the devices they power work!