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matt down south
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Joined: 20/10/2007
Location: Australia
Posts: 50

Posted: 05:40pm 05 Dec 2008

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hi all
decided to gut the magnum 8000 mod square wave inverter to make a decent size 24v battery charger using the centre tapped transformer which puts out 36.3 volts open circuit using both sets of windings [18.15 per leg]and feed that into some car alt diode packs and than through a tristar ts 60 reg set on solar mode,in inverter mode the specs say for 2.4kva output it comsumed 120 amps input feed into both windings so im a bit concerned it could have to many amps output for my 60 amp voltage regulator would that be right?as i dont want to blow the smoke seals on a new controller!

matt

oztules

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Joined: 26/07/2007
Location: Australia
Posts: 1686

Posted: 09:29pm 05 Dec 2008

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If your transformer is putting out 36vac from 240v ac mains, and looks very big...then I would probably try this.

Hook up your diode bridge to the secondary, put amp meter in series with the batteries. Simple so far.

Now. The easiest way to regulate the power output is to use... you guessed it, capacitors.
Grab some run capacitors from some old cap start cap run motors, and put them in series with the mains 240v active... Not the start caps (non-polarised electrolytics.. they will not survive very long ..usually black or blue) The run caps are usually white.

This capacitor (start at say 10uf) will limit current and give you a reading. You can add or subtract capacitors as necessary to get it to the output max current you require, and so keep inside the specs of your controller.
Once you have a happy value, you can install your tristar

If this transformer was used as a multivibrator step up transformer, they will have wound it tightly coupled.. which is exactly what you don't want in a battery charger transformer. It would be unusable if connected normally, as it would over charge to hell when the batteries were flat, and barely charge them when nearly finished.... at 36v into a 24v pack... flat, say 20v, it would blow every fuse in the house at startup.

In the case of 36v ac input, it would still be blowing fuses at 28v state if charge.... but if you just unwound some turns to get it to 24v, it would still act very unreasonably.... too much at start , too little at finish.

Battery charger transformers are loosely coupled for this reason. They must deliver reasonable current over a broad range of voltage. If there is a lot of "slop" in the magnetics, then at low batt voltage, the leakage will keep our current tolerable until we get the volts up a bit, and we will have wound for a slightly higher voltage to compensate for this.

At equilization voltage, it will still be putting out some useful current, the tight wound one would not.

Thats why I think the caps will be the cheapest simplest way around this problem... otherwise current regulated SCR or Triac control would do it... or on the DC side, a very large chopper circuit... or a very big tristar.

.........oztulesEdited by oztules 2008-12-07

Village idiot...or... just another hack out of his depth

matt down south
Regular Member

Joined: 20/10/2007
Location: Australia
Posts: 50

Posted: 06:25am 06 Dec 2008

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hi Oztules
thanks for the very informative reply,the ex inverter transformer sounds like my friday night customers i take pizza out to [their a nicer mob on saturday]sooo can a use a varichoke based hi/low amps stick welder as i have 2 to choose from
1]home based up to 10 guage rods vari amps and hi/low amp settings or
2]industial 240/480v up to 8 guage rods vari amps and hi/low amps gruntmaster i also have a oiled cooled 6 amp settings up to 8 guage rods
so would any of these do the job for battery charger duties?or would a pair of 9.6v @20a c/tap trannies using 3 sets of windings [28.8v]be kinder to my lucent 600ah gell filled ex onetel batteries and controller?

matt

oztules

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Joined: 26/07/2007
Location: Australia
Posts: 1686

Posted: 01:51pm 06 Dec 2008

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Unfortunately I can't comment on the charge regime of gel batteries.

I also don't know how your controller works. I have had lots of experience with wet cells, and my chargers were transformers I made with the right characteristics to bulk charge at lower SOC voltage and taper off as the float voltage was reached, then a timed equalise charge.. then turn off. Yes, traction packs. (forklifts etc)

I don't know how the modern fancy ones work.

If they are intelligent PWM things, they may do all the work for you, in which case, you could take some turns of your inverter one... but that may still over current it...hmm

Check the input volts of the controller, and the output of the welder ones (and current), and see what you have to work with.

If it were mine, I would probably rewind the inverter one with the primary and secondary separated by as much as I could, and drive it with that. The pwm thing should have a best input voltage, and wind for that. The separation should soften the current considerably... loose coupled. Make extra turns on the secondary so you can peel a few off if you have too much voltage.

You only need 1.5kw output, so you should get a little room in the winding window for separation at the lower voltage you will need.

Sorry I can't be more helpful, but I have no experience with that kind of controller or gel cells..
.. but someone else will.

..........oztules

Village idiot...or... just another hack out of his depth

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