using flexmax charge controller with 36 volt DC generator

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using flexmax charge controller with 36 volt DC generator

Postby gene1949 on Tue Oct 30, 2018 3:04 pm

I have a flexmax60 solar charge controller (currently not in use) and am wondering if I could use it with my 36 volt DC generator which does not have voltage control. It is a Zenith welder with open circuit 72 volts and working voltage around 32-36 volts. Amperage is adjustable and output is stable much more so than a wind generator. The question is will the charge controller work with pulsed dc as opposed to battery straight line dc? My guess is the mppt function may still work.
Since the flexmax 60 is no longer needed I would like to try this experiment providing it wouldn't smoke the charge controller. Warranty not an issue as it's expired.
Any help would be appreciated
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Re: using flexmax charge controller with 36 volt DC generato

Postby Kurt Lundquist on Wed Oct 31, 2018 7:31 am

What is your goal?

-Kurt
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Re: using flexmax charge controller with 36 volt DC generato

Postby gene1949 on Wed Oct 31, 2018 10:43 am

Hi Kurt
My goal is to use the the DC generator to charge my batteries. I have an unusual situation as my 60 acres is surrounded by lava here in Puna Hawaii. Everything has to be packed in right now literally on my back until new access can be established which is months or years down the road. My Trace 4024 finally quit charging mode after 18 years of use. The DC welder generator is the only DC source besides besides my solar panels at present. Currently I am using the DC generator welder to charge my simpliphy batteries but I have to monitor it manually very carefully so as to not overcharge.
I could helicopter in the proper equipment etc but the financial hit I have taken is enormous and would not be cost effective right now.
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Re: using flexmax charge controller with 36 volt DC generato

Postby Kurt Lundquist on Wed Oct 31, 2018 3:22 pm

Ok I think I get what you are going for. To confirm, you are looking to use the DC generator as the voltage source input to the FM60 instead of a PV array. The idea is the controller will regulate the DC generator charge to the battery bank.

Is that correct?

First I will say this has not been tested so your mileage may vary. As you say in your first post you realize this would be an experiment and you are already out of the warranty coverage period. My initial thought is the FM60 is designed to work with a current limited DC source. Of the top of my head, I think the max input amps is listed at 48 (this is listed in the manual if you want to confirm). You will need to make sure your DC generator does not put out more amps than the controller input can handle regardless of the voltage. It sounds like you can limit current on the gen so that would help. A resistor in series with the input circuit would probably be a good idea as well.

Next issue is when the FM60 tracks a PV array it attempts to harvest amps at various voltage points as it searches for the MPP. Your generator might not react to this very well. If you proceed I would disable the MPP function by setting the U-Pick mode in the Advanced menu. The FM manual talks about this on page 100 where it references using the controller with a micro-hydro system.

I've seen FM's work with a full bridge rectifier chopping up 120Vac to feed into the PV input. On those setups, I believe a capacitor was installed to help smooth things out a bit.

These are just my thoughts on your application. I do not work for OutBack and I cannot give you any confirmation that your controller will not smoke or generator die even if you follow my advice. Sorry for the disclaimer but my moderator role in the forum often makes people think that I represent OutBack engineering which is not the case.

Let us know what you decide to do.

Good luck!

-Kurt

PS: Here is a link to the manual
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Re: using flexmax charge controller with 36 volt DC generato

Postby gene1949 on Wed Oct 31, 2018 5:43 pm

Hello again Kurt
Yes you got it right about why I want to try using fm60 to regulate voltage and amperage. Your input is greatly appreciated and knowing others have used pulsed DC with flexmax is a big help as well as starting off disabling mpp which I will do. If I elect to try leaving mppt on I will turn down to dc gen amps to less than 5 or 10 amps and watch closely what happens with my finger on the disconnect breaker.
I do understand your disclaimer and I would do the same. I can live without fm60 as I have a backup if it smokes.
Thanks Again ! This is a great forum!
Gene
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