Author Topic: Toroid isolation transformer  (Read 4098 times)

tim.moore

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Toroid isolation transformer
« on: December 23, 2009, 04:19:33 AM »
I got some new advice on my problem with the Russco charger.  Lee Hart of EVDL said I need to put an isolation transformer in front of the battery charger, so as to make the Russco isolated.  Does anyone know where I might obtain a Toroid isolation transformer in the area?  The toroid website showed a simple plug in model, I am holding my breath and hoping that is all that it is, though few things are plug and play with EV's.   In terms of my specification, I am running 120v AC and my pack is 126 vdc.

ted.lowe

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Re: Toroid isolation transformer
« Reply #1 on: December 23, 2009, 07:58:56 PM »
Ouch... that sounds expensive at that wattage (up to 2.5kw)!  Can you explain more (or paste his response)? Lee Hart is an EV guru, but there has to be a better way!
« Last Edit: December 23, 2009, 08:01:23 PM by ted.lowe »

rich.carroll

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Re: Toroid isolation transformer
« Reply #2 on: December 24, 2009, 12:30:27 AM »
John E., John J., Steve and I discussed your problem over morning coffee.  We (collectively) suspect you still have a ground fault problem, likely in your battery pack.  I know you have super cleaned, then recleaned, and even cleaned the batteries again, but what you reported to John E. seems to indicate a ground fault problem.  John said that there is a measurable voltage when the most positive and most negative battery cables are isolated, and when measured from chassis ground to places in your battery pack.  I agree with your method of measuring voltage (potential) between places in the isolated battery pack and the chassis.  The ground fault is certainly (but obviously, not obviously)  ;) where the voltage between the pack and the chassis go to zero.  The fault is usually on the top, but could be a track down the side of the battery, either a crack, or a miniscule carbon track.

Our solution:  Identify the battery or batteries where the measured voltage from the battery to the chassis is zero.  It is likely that battery or the one next to it.  Remove it, and carefully wrap it in a plastic bag, even a garbage bag.  Trim, and reinstall.  Then remeasure all possible voltages to see if some other battery has a similar but lesser problem.

You could also measure the resistance between the battery cable and the chassis where the ground fault is indicated.  That resistance should theoretically be so high, that no voltage could be measured, but check the resistance.  If it is real high, it is usually not a worry, but we know the Russco chargers are sensitive to ground fault errors.  You need to do what ever it takes to make the resistance between the battery and the chassis so high that the Russco does not identify this as a ground fault.

If you are really tight for room, and there isn't room for an insulating bag, try to paint the surfaces involved.  A good thick coat of strong enamel that wears well would be my choice. 
Rich Carroll                           rc@rc.to

tim.moore

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Re: Toroid isolation transformer
« Reply #3 on: December 24, 2009, 01:17:50 AM »
Ouch... that sounds expensive at that wattage (up to 2.5kw)!  Can you explain more (or paste his response)? Lee Hart is an EV guru, but there has to be a better way!

 Russco charger... a problem with the GFCI tripping despite
>     doing
>      >     all of the things Russ has told and all of the things the
>     guys in my
>      >     FVEAA group have told me.  Russ said you isolated the
>     batteries from
>      >     your battery box with a polyproplene box.  Could you explain
>     this to
>      >     me more.
>      >
>      >     As you know, the Russco is a non-isolated charger. There is a
>     direct
>      >     path from the "hot" AC input to the DC output. If there is
>     any path
>      >     from anything in the high voltage wiring to chassis ground
>      >     (batteries, motor, controller; anything), it will trip the GFCI.
>      >
>      >     I've been building and driving EVs for years. I have found
>     that no
>      >     matter how hard you try, flooded batteries will always develop a
>      >     conductive acidic film. The carbon dust from brush wear in a
>     motor
>      >     will also form a conductive film. So, ground faults are
>     inevitable.
>      >
>      >     I have switched to isolated chargers for this reason. It's
>     not hard.
>      >     You can add an isolation transformer ahead of the Russco, and no
>      >     more GFCI tripping. But, this is a 20-30 lbs transformer that
>     will
>      >     cost $100 or so. The one I used is a toroid that weighs 23
>     lbs and
>      >     costs $75 (let me know if you want one).
>      >
>      >     The other option is thoroughly insulate the batteries from
>     ground.
>      >     My previous EV had a metal battery box with with flooded golf
>     cart
>      >     batteries. I got some 10 mil polyethylene sheet, and folded it to
>      >     make a  "bathtub" liner for the battery box. By folding up the
>      >     corners, it would hold water without leaks. That's what you
>     want to
>      >     be sure there are no holes.
>      >
>      >     I installed *two* of these liners (insurance; in case one
>     leaked). I
>      >     punched a hole in the center, and installed a plastic pipe nipple
>      >     that went through the battery box and out the bottom of the car.
>      >     This was so I could wash down the batteries, and the water would
>      >     drain out the bottom without ever touching the metal battery box.
>      >
>      >     Then I lined the battery box with 1/2" thick white "bead board"
>      >     styrafoam (for insulation, and to take up the extra space so the
>      >     batteries were tightly wedged in place). These batteries were
>     used
>      >     for 7 years, and never developed any leakage to ground.
>      >
>      >     For my present EV, I had a plastics company make me a 5-sided box
>      >     out of 1/4" thick polyethylene, plus a lid with a 1" flange
>     around
>      >     the sides. This sits in my battery racks, which are made of
>     1.25" x
>      >     1/8" thick angle iron. Again, with flooded batteries I have
>     had zero
>      >     problems with leakage current from the batteries.
>      >
>      >     The motor is another story. It is inevitably grounded, so all you
>      >     can do is blow it out with compressed air once in a while when it
>      >     accumulated carbon dust, dirty water from the road, or other
>      >     contaminants.
>      >
>      >     Hope this helps!

tom.gralewicz

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Re: Toroid isolation transformer
« Reply #4 on: December 24, 2009, 02:09:48 AM »
I have a similar problem with my charger tripping a GFCI when I plug it in.  If I then reset the break it works fine.  I am using a system with 1 charger per battery.

The next clue came when I was changing 1 charger and got a shock when I touched the grounded charger and a battery terminal.  My assumption is that I had a short to the car chassis somewhere.  I grabbed my DVM and checked for a voltage between the battery terminal and the chassis.  There was over 100V! (a bit of a surprise since the shock I got was rather small) So I started moving across the pack to localize the short.

The readings didn't make sense, I read almost the same voltage everywhere.  So while I scratched my head I left the DVM connected and in a few seconds saw the voltage drop!  all the way to 0!

My current theory (pun intended) is that the large metal car and the collection of lead plates in the batteries make a nice capacitor.  Driving charges things up (static friction, RF noise from the controller, or ?)  As I haven't been driving the car due to the lack of a heater I haven't gone much further with this problem.   I expect a large (10M ohm) resistor between the middle of the pack and the chassis should clear up the problem.  I hope to spend some time next week working on this.

Tom





todd.dore

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Re: Toroid isolation transformer
« Reply #5 on: December 24, 2009, 03:59:19 AM »
I too noticed this problem today.  It also happened on Electric Blue.  At one point in Electric Bug, I get 122V when measuring battery post to chasis ground.  Anyway, the resistance doesn't show up, so I think it is a very weak ground fault.  At some point I may thoroughly clean the wet muck off the battery cases, but that's a big effort.  Hopefully, I can just take out the batteries and install the Lithium batteries that I plan on buying (would be nice to have a local importer - hint George H).

Anyway, if all goes well, I'll be using Lithium Iron Phosphate by the end of 1Q 2010 and won't have the problem noted above.

nathan.stowe

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Re: Toroid isolation transformer
« Reply #6 on: December 25, 2009, 04:01:50 PM »
Hi guys, 

I have never had the ground fault problem myself, but I learned from the EVDL that putting a plastic sheet under/around the batteries to completely isolate them from the chassis seems to do the trick for the old timers.  Even if one gets behind on the maintenance/cleaning.  I have this in my EV and can share details if you wish.  (maybe even some plastic sheet left too)

Also if you are just trying to isolate the pack many 1:1 transformers should do the trick.  I believe that the toroid ones are the variable ratio, which as you have found are not cheap. ( I could be way off base here too)

Nathan