Renewable Energy Questions/Discussion > Renewable Energy Q&A

Capacitive battery charging

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WooferHound:

kurt:
zubbly was playing with that when he died but he was smart enough to use an isolation transformer on the input for safety

rossw:
You could have left the last part off that, Kurt, and let it serve as a warning!
Statement of fact.... and an suitable warning!

"Zubbly was playing with that when he died"

Rest in peace our friend. Gone, but not forgotten!

oztules:
It is quite a simple and effective circuit Woof...

It would be nicer if it were isolated by a transformer

The use of caps to control AC currents is very widely used now days, but mostly for small power supplies in range hoods and other domestic appliances where they are too slack to use a tranny or a pwm isolated solution... it goes without saying it needs to be double insulated to get away with this on a commercial level.

So I agree with Steve, that lack of isolation is a problem, but I won't pretend it is the end of the earth or a game stopper.

There will be many instances that this can be used quite safely, but house banks and other systems where the battery cannot be isolated from ground or people is not one of them.

A gentleman on the old fieldlines used this technique to charge his EV every night.

You would think this would be a death trap, but in fact if you know what your doing, is perfectly safe. Remembering the neutral is grounded anyway, we know one side of the battery is grounded already.

Providing we choose the active to go through the cap and to the non-ground end of the bank, and it is half wave with neutral grounded.... it is perfectly safe..... as the battery is already at high DC voltage, touching it would frizzle your hair without the AC component to worry about. The half wave will cut the available energy to half before we regulate with the cap.

It would be tempting to think that the capacitor in this case probably mylar aluminium will stop the conduction across the dielectric gap, and so give isolation to say the active side, and the neutral is already earthed anyway......... and so safe ... yeah???........NO.

The electrons going into the cap are not the same ones coming out to do the work it is true,  they are new electrons, the result of displacement current through the cap, but do not provide any isolating properties. The current limiting is a result of the capacitive reactance of the cap, so current is controlled by the amount of uf used and the frequency of the system or XC= 1/2piFC.

So we have effectively controlled the current without the losses associated with a resistive impedance with a capacitive impedance.

So really the only downfall is the isolation problem, and thats only a problem where folks can get their mits on the system .
In isolated cases this can be a perfectly valid way of doing things.

I cannot join the chorus of folks that worry the sky is falling if we don't get protected from every little thing, but would rather get involved with saying how it could be done  with the least risk... which is a different perspective.

The number of folks getting fried from this sort of thing, pales into insignificance compared to auto accidents and shootings in the US. There are far more urgent things to get excited about than this. Consider that only 325 or so people die from electrocution in a population of 300 million annually...  interestingly over 50% of those are smart people who work in the electrical industry daily.... who should know better, the other half are people who know nothing, but play with electrical stuff every day...and plenty of them in dubious circumstance from what I see on the telly from time to time.

And I am totally baffled by the veracity of the  power factor comments...

Evolution will sort it out eventually anyway.... there are always the Darwin awards to look forward to..... although the modern RCD's will probably stop evolution from weeding them out as it should.



................oztules

rossw:

--- Quote from: oztules on October 04, 2017, 06:28:00 pm ---Providing we choose the active to go through the cap and to the non-ground end of the bank, and it is half wave with neutral grounded.... it is perfectly safe..... as the battery is already at high DC voltage, touching it would frizzle your hair without the AC component to worry about. The half wave will cut the available energy to half before we regulate with the cap.

--- End quote ---

Agree with everything you said, Oz... except this bit.

Series capacitor and half-wave rectification?
Without other components, the cap will quickly charge up and not pass any further current.

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