# Charging batteries with a modified AC generator (genset)



## boekel (Nov 10, 2010)

Does anyone have experience with this idea?

Using a 'normal' (industrial) genset to charge a hv battery, directly connecting the battery through a rectifier, and regulating the output of the generator by replacing or 'tricking' the AVR

Normally the AVR (Automatic Voltage Regulator) does two things:
-Regulating the voltage to the set value
-Lowering the voltage when the frequency drops (from a to big electrical load) so the combustion engine driving the generator gets a break and can restore rpm

The AVR does this by varying the voltage on the stator.

Now if you would rectify the AC from the generator with a 3 phase rectifier, and feed this directly to the battery. An adjusted AVR could be used to set maximum power / voltage. the rpm of the genset could be controlled to adjust to the power needed.


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## onegreenev (May 18, 2012)

PM sent. You can check my blog for some ideas I have and my videos on using DC sources to charge my pack. One from my stationary battery bank and also using my welder. For generator charging most will just plug in their chargers. There needs to be a way to control the voltage and current into the pack.


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## boekel (Nov 10, 2010)

I currently have a diesel-electric setup of about 65 kW (in my boat)

I will replace this with a serial-hybrid setup using 1 or 2 DMOC645 / Siemens motors to drive the propshaft.

For delivering power / charging I'll need a minimum of about 50 kW continuous. I could just use another Siemens / DMOC combo to make a generator (because they are available for a decent price), but using this would be a bit of overkill IMHO

I have a 75 kVA Cummins-Stamford generator installed, so if I can use this machine to produce enough DC at the right voltage it would be great (I know, voltage would probably be to high at 1500 RPM, etc.)


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## aeroscott (Jan 5, 2008)

I've lived with generator power (off grid)for over 20 years and have dealt with generators and regulators . My latest generator used a 1 cylinder diesel engine turning a pm brush motor(24 volt) . I was charging a 48 volt pack.Motor/gen needed higher voltage winding so I just charged 24 volt/half pack until a higher voltage motor could be found. Operation was to close the connection with battery thus motoring the engine then adjust the engine speed to get my amps /volts in the range. 
Chevy volt and Preius use pm alternators which have higher efficiency then a wound rotor generator has. I don't know how they regulate them.
I have a BMW 2.5 6 cylinder diesel that I want to setup as a pm generator.


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## skeeterb (Feb 6, 2009)

I've been thinking of something along the same lines. I was thinking of something that had to be compact, durable, and scalable. The compact part is the important thing for me because I want it to be able to fit into the former engine compartment of the car. But durability and scalability are also important too though, I want to be able to be able to change the voltage output if required for the project. I was thinking of using an electric motor that can turn at the required RPMs and torque to keep the genny turning. I'm still working on how to control the motor to start it and keep it running.


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## akseminole (Jan 5, 2014)

I was thinking about using a welder generator that can output 480v, isn't that what they power fast charge stations with?

http://www.wayfair.com/Miller-Elect...-LP-4-Cycle-OHV-Engine-907255011-MLR1220.html

Granted, it's big and heavy and won't fit in a engine compartment, but it Would fit in a trailer for range extension purposes. 

Idk, it's just a thought to put out there.


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## cts_casemod (Aug 23, 2012)

Directly attaching the genset output to a rectifier is technically going to work, but it's not efficient.

Generators are rated in KVA rather than KW. A rectifier only pulls current once the peak of the sine wave is larger than the battery voltage, so the apparent power can be many orders of magnitude larger than the real power.

That means a generator rated for something like 3KVA might be able to supply something in the lines of 1.2-1.7KW of useful power to a rectifier system.

To improve this scenario one needs to add a PCF front end to the genset, so that means using the charger will always be more efficient than directly attaching the genset to the battery. 

The AVR could still be used, but more efficient would be to open the throttle fully and let the generator speed change in function of the charger load (keeping the field coil power constant, rather than changing it to match the demand) This works well during the CC charge phase and offers the greatest efficiency.


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## boekel (Nov 10, 2010)

Thank you cts!

Do (large, 50-150 kVa) VFD's generally have PCF correction?


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## cts_casemod (Aug 23, 2012)

boekel said:


> Thank you cts!
> 
> Do (large, 50-150 kVa) VFD's generally have PCF correction?


 They generally do, but mostly use a bulky inductor to improve crest factor/conduction times (and therefore PF) rather than an active system.


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