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Old 06-12-2018, 03:51   #1
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Generator (3 phase AC) to constant voltage DC charge controller for LiFePO4

Hi,

I am thinking about extending our energy generation on Entropy with a Hydro Generator to charge our LiFePO4 battery bank when cruising.

The following question came up after doing some research on charge controllers for electromagnetic generators such as wind gens or hydro gens available for boats. Apart from COTS solutions there are some interesting smaller vendors for Hydro Generator Turbines which I am currently considering for this purpose. Most of them offer a charge controller for the turbine, but this is always designed to charge Lead Acid battery chemistries.

This got me thinking about obtaining the Hydro Generator 3 phase AC turbine and buying a suitable charge controller from a different vendor/sector - if such a thing exists at all.

As you may know LiFePO4 like to be charged to a set point voltage and then charging should stop. There is no need for fancy charging profiles in this case.

So now I started searching for a magic device which fulfills the requirements for charging a LiFePO4 bank from a generator type energy source. (It should not really matter if this is a wind or a hydro generator.)

I have identified the following requirements:
  • Raw generator AC raw voltage range is not known yet, as I have not chosen the turbine yet, but it will be likely less than 50 V.
  • The charge controller should ideally accept 3 phase AC. However it would be possible to add an external rectifier and feed the charge controller rectified AC (i. e. very choppy DC).
  • The charge controller should ideally use MPPT and buck voltage regulation for efficiency reasons.
  • The charge controller should produce a clean and constant 13.8 V (or better yet, adjustable) voltage when only lightly loaded (i. e. near 100 % SoC of the LiFePO4 bank). There should be no voltage spikes above the voltage set point (which could lead to unnoticed overcharging).
  • The charge controller should be resistant to a short on the load side (which is basically what a LiFePO4 with < 100 % SoC is to a charging source) and be able to protect the generator from overload. This basically means that the charge controller should have an adjustable output current limit.
  • The charge controller should ideally provide a digital input for shutting off the power output to the main load output, diverting it to a heating element attached to a "dump load" output of the controller. (However, this could also be done by external circuitry such as a make-before-break toggle relay between charger and battery load/dump load.)

If anyone knows if such a miracle device exists it would be great to hear about this.

If nothing is available on the market maybe it's time to eventually get out my rusty EE circuit design skills
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Old 07-12-2018, 09:02   #2
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Re: Generator (3 phase AC) to constant voltage DC charge controller for LiFePO4

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Originally Posted by mbartosch View Post
If anyone knows if such a miracle device exists it would be great to hear about this.


I take this as a "Sorry dude, you're on your own.".
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Old 08-12-2018, 06:56   #3
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Re: Generator (3 phase AC) to constant voltage DC charge controller for LiFePO4

I think you and Bill Thomason should put your heads together on this.
VSR Alternator Regulator
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Old 10-12-2018, 09:31   #4
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Re: Generator (3 phase AC) to constant voltage DC charge controller for LiFePO4

Erm, his name is Al.
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Old 10-12-2018, 14:36   #5
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Re: Generator (3 phase AC) to constant voltage DC charge controller for LiFePO4

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Originally Posted by rgleason View Post
I think you and Bill Thomason should put your heads together on this.
VSR Alternator Regulator
Thanks for the link. I pondered this and decided not to go this route.
The main reason is that the project has apparently gone closed source. If it were still OpenSource I would have probably gotten involved.

The second reason is that an alternator regulator is somewhat different from what is needed for this purpose. Some of the circuitry of an alternator regulator (e. g. voltage and current sensing) might be reused, including some of the source code of the regulator, but significant portions of the system would have to be different:

An alternator is an externally excited generator. The regulator will be able to adjust output power and generated voltage by controlling the excitation field of the alternator. Power generation can be cut down to zero by cutting the field excitation.

A wind or hydro generator is permanently excited via powerful permanent magnets. There is no way to regulate generated power at a given rotational speed, hence the need for dump loads with wind or hydro gens.

So building a regulator for wind or hydro generators will require different circuitry and a different regulation algorithm compared to an alternator regulator.

Will consider doing some R&D on this topic if I find the time.
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