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Author Topic: Inverter welder as battery charger …. Will a choke break it?  (Read 2942 times)
Dyslexicbloke
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Blue sky thinking ...


« on: May 06, 2011, 03:58:51 AM »

Hi folks, I run a small inverter based welder connected to my genny as a battery charger.
I’v been doing it for ages and have a small mod on it that allows me to control its output current so that I can maintain a stable charge voltage.

My first set of batteries were all scrap automotive and I wasn’t to bothered about being nice to them so never bothered about the ripple but having just bought some good, I hope, second hand cells I would like to add a choke to shift the 0.8v ripple I get.

I am pretty sure I can wind / acquire a big choke without too much bother but I am unsure if it could damage the welder by fitting it.

I will also be adding some huge caps I have to the battery bank to provide a low impedance path for the offending waveform.

Any and all thoughts will be apriciated.

Alistair
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Off Grid - Big Caravan and huge enclosed gazzebo.
300W PV 12V system.
400Ah of AGM Absolyte GP cells. (Second hand)
600W Inverter (Maplin's finest :-) )
CHP in the works - Chinese Horisontal Diesel [S195 Generic - Kukje]
VAWT testbed flying - Back to that when its warmer I think.
johnrae
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« Reply #1 on: May 06, 2011, 11:03:09 AM »

The choke shouldn't bother the welder since all you are doing is buffering the ripple from passing through, so to speak.  As to fitting capacitors across the batteries, I feel that would be a waste of time and money since the battery impedance is exceedingly low and in any case, to gain maximum benefit from an LC filter you really need another choke after the capacitors as well.  ie welder then L then C then L and then batteries.  What sort of charge currents are you looking at.   Your main problem is in relation to control of system voltage and current to prevent cooking your batteries.  I would have thought you needed some form of regulation device so's you can connect and forget.
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Dyslexicbloke
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Blue sky thinking ...


« Reply #2 on: May 06, 2011, 02:47:55 PM »

Good info, thanks, I didnt know about the L-C-L thingy but it makes sense.

I have 3 X 2200 uF electrolytics rated at 450 DC that I pulled out of a dead UPS years ago, I wasnt planning on buying anything if at all possible.

I also dont have any idea how big the choke would have to be, I was sort of planning on trying a few turns around a torroid core I have but I apriciate that I may well have vastly underestimated the size. I am simply working on the premise that I have seen big chokes wound with 20 - 30 turns in large chopping supplies but it is entirly possible that I am just missing the point.  What I know about the theory here you could write on a verry small thing...

Max current will be circa 80A but I am more worried about the ripple once it has significantly dropped as I aproach float VPC.

Could both choke windings be on the same core, asuming I can get enough turns on them, if they were the same way up the wouldnt they summ and reduce the total number of turns required ....

              | - Caps - |
Winding> -               - Winding >
=========================               Where " ==="  is actually a torroid.

The core is about 80mm OD 40mm ID and about 25mm deep.

The welder has a remote curent setting device, OK bodge - its a motor driven pot, that my PLC is quite capable of adjusting to keep the voltage in check.
Its pulsed up or down with a pair of open collector outputs so I can shift it quite quickly id necessarry but still have a suprising amount of control by varying the pulse width. Hardly high teck I know but it works and didnt require much modification of the welder, in fact it is using the origional pot.

I do know it will ware out the track rather quickly but I will cross that bridge when I come to it perhaps something a bit more high tec next time.

Alistair
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Off Grid - Big Caravan and huge enclosed gazzebo.
300W PV 12V system.
400Ah of AGM Absolyte GP cells. (Second hand)
600W Inverter (Maplin's finest :-) )
CHP in the works - Chinese Horisontal Diesel [S195 Generic - Kukje]
VAWT testbed flying - Back to that when its warmer I think.
Dyslexicbloke
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Blue sky thinking ...


« Reply #3 on: May 06, 2011, 08:30:45 PM »

An update un progres with the choke .....

I just put 20 turns of 6mm trirated on the to the troid I mentioned, just the one winding, no caps at all.

The ripple, which is at about 17KHz has reduced from about 800mV to 300mV with a charging curent of around 55A.
The choke is warm to the toutch but given that the cable is only rated for 32A it probably that as much as anything else.
I am going to have to get some huge enammled wire.

So now I have some diferent questions ....

If I double the nunber of turns can I expect a further significant reduction in ripple?
and
How much ripple is actually too much?  (400Ah high current AGM's in 2V cells)

Also,
My inverter, 12>240AC not the welder, is causing a ripple of about 20mV at about 120Hz, is there any point in putting a choke on the DC feed to it?


Anything anyone can offer will be very much apriciated, I am well out of my comfort zone here.

Thanks, Alistair
Logged

Off Grid - Big Caravan and huge enclosed gazzebo.
300W PV 12V system.
400Ah of AGM Absolyte GP cells. (Second hand)
600W Inverter (Maplin's finest :-) )
CHP in the works - Chinese Horisontal Diesel [S195 Generic - Kukje]
VAWT testbed flying - Back to that when its warmer I think.
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