Rectified Generator smoothing capacitors.

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robsmith asked Jan 3, '19

Rectified Generator smoothing capacitors.

Hello all,

I am new to this community and this is my first post... I hope it works.

Earlier today i spotted a Facebook link to an article by John Rushworth about a hydro electric setup by Markus who is registered on here too.

It looks like a three phase alternator on the hydro turbine and I can see a bridge rectifier and some capacitors, presumably for smoothing.

I have just finished putting up my solar panels but over the last few weeks of gloomy weather we had only half of our solar panels up and running so had to resort to using an awful diesel generator to keep our batteries alive.

The generator is a single phase 110v ac site generator with two sets of windings in series to give 110v ( 55v - 0 - 55v). I have configured these in parallel to give a 55v ac output. This then goes into our battery shed and through a home made bridge rectifier using four big stud diodes. From this it goes straight onto our battery bank without smoothing. The battery bank is flooded lead acid 48v 450ah and I am charging at around 30 amps from the generator. That is the limit of my undersized lash up wires. The generator can give more. I am using the generator as a backup to keep the batteries up over about 60% SOC if the solar panels are not producing enough in dark weather.

I did have 30 nice Rifa capacitors lined up for the job but the chap I was in contact with about them unfortunately died. His sons who now run the business are less generous, so I think I have lost those now.

Should I worry about smoothing?

@Markus

Generator

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Answer 1 · 2019-01-03T22:45:03Z

markus answered · Jan 03, 2019 at 10:45 PM

Hi @RobSmith

welcome here.

Yes, those capacitors are there, to smooth the MPPT input voltage a bit. They should be good, for the voltage tracking circuit in the MPPT charger.

In your case, the generator is connected directly over the rectifier. 55V AC after rectification, can get up to 77V DC. This is a dangerously high, charging voltage. I would suggest, to use a charge controller.

If you are manually monitoring the charging process, it will work without an extra charger to do some bulk charging anyway, but it is not so comfy in my opinion. And you are in danger of damaging something, if you do not turn off in time, and the voltage gets too high. You can also have a big voltage ripple on your DC circuit, this is not good for some loads and not ideal for the batteries. Capacitors will help, but they are no "universal solution".

I would think of using an MPPT charger after the rectifiers, but this is no officially supported solution and nothing I would do, if I am not 100% sure, how to.

Regards,

Markus

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Answer 2 · 2019-01-03T23:13:58Z

robsmith answered · Jan 03, 2019 at 11:13 PM

Hi Markus.

Thanks for the reply.

I have a charge controller on my solar panel input but not on this generator. I could have run the generator power through the charge controller but I did not want to do that without smoothing out the dc so bypassed the charge controller.

The generator is so noisy I can never forget it is running and I monitor the battery voltage regularly. At just 30 amps it takes hours to get the battery voltage to rise. The engine is awful so I am quite keen to turn it off as soon as possible.

I think I shall get an oscilloscope and actually measure what is happening. My Fluke multimeter measures dc but that is an rms value so doesn't show me the peak. I not sure if the battery bank just pulls the peak voltage down. Maybe my too thin temporary wires are helping in that respect. The engine has some govenor adjustment on it. I just use a spanner on this to bring the wires upto a warm temperature which is about 30 amps. I am just using it to keep the batteries above about 60% SOC on dark days. The solar panels got the battery bank nearly fully charged yesterday in the sun.

My plan is to remove the 55v generator from its terrible noisy diesel engine. I will then power the generator from a far quieter volvo car engine running on wood gas. This will have sensible automatic controls.

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markus ♦♦ commented · Jan 03, 2019 at 11:23 PM

This sounds, as you are on the right way. Measuring what's going on, is always best.

A car engine might not be ideal, as it is made for cars. And is in most cases, too oversized for the system to reach a good overall efficiency. I would suggest, to use a smaller, industrial type diesel engine (e.g. small excavator engine or similar).

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markus ♦♦ markus ♦♦ commented · Jan 04, 2019 at 09:04 AM

If you manage, to run your diesel engine on wood gas, I would love to read about it.

Regards,

Markus

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