Isolation transformer heat.

[Jerry]

A year or so ago when the pulse charger discusion was going on I had built several types.

My favorite is the capacitor, fullwave bridge, AC line type. This unit can be concidered very dangorus.

I first saw it here on the board. The problem was its connected directly to the AC mains with no line isolation and with no battery load open voltage will go very high.

Thats not a safe combonation. For my own use I had no prblem using it this way. As a matter of fack I use it this was on my golf cart and 85 Ford ranger E-truck. Never been shocked off of either one.

However a freind with a 60 volt battery bank wanted one. This made me nervus. I deducted I'll atleast need a large isolation transformer with this charger perminet hard wired and conected to the AC mains through a GFI unit.

I had no high powered line isolation transformers and new unit were way to pricey.

An idea hit me about modifieng microwave oven transformers. I took to of the same phisical size remove there primary and secondary coils. Then I place the 2 primary coils back on one of the laminations.

WAL-LA, A high powered 120v to 120v isolation transformer made from 2 throughaway microwave ovens.

The problem was however they run very hot. I just figured out the heat problem.

I'm not sure what you call a transformet when the primary and the secondary coils are seperated by a stack of lamination between.

When I reasemled the 2 coils I would push them close together and fill in the gap at one end with lamination stacks.

This week I've built 2 identical transformers, however I left the filler lamination segments out of one transformer. That transformer runs very cool and has about 1.5 amp higher out put.

I've posted this story because if I remember correctly several of you tryed the same conversion and had extream heat problems. I've had the heat to but I've been using very agresive fans directly on the transformers. It was seeming that the laminations were getting hot but not the coils?

I've asumed it must be heavy Eddy currents, the space, and gap dosen't hurt preformance, the heat goes away and the transformers is way more eficient.

I'll be building a few more in the future to confirm my findings.

MeanwhileI like how these pulse charger/desulphaters work.

                          JK TAS Jerry

[oztules]

Hi Jerry

I had the same problem.

If there are laminate plates between the primary and secondary, they tend to limit the curreent transfer from primary to secondary (they short some of the magnetic field from seeing the secondary a bit to a lot.... depends on the no of plates) This can be useful for battery charging directly, as it will give you a larger voltage swing without severly overloading (With tight coupling at low battery volts will be drawing lots of current, and hardly charging at high battery volts) With the shunt in place this evens out the current a bit (loose coulped transformer).

With your setup, it will be of no use as the capacitor effectively controls the current .

Most of the heating is from the welding on the laminates. If you can stop shorting the plates out (use a different method of rebuilding the laminates, this problem largely dissapates.

By welding the plates together, they are easy to build, but are then prone to overheating even with no load at 100%duty cycle (ie microwave oven does not tend to work 8 hrs straight.)

Take out the short citcuit from the welds, and it should run cool..... at least mine did that I converted to a 36v battery charger. It was stinking hot with the welds, cool without them.

Mine didn't have shunts in it either.... I wanted more current.

..........oztules

[Jerry]

Hi oztules.

In these last 2 transformers I did not weld the lamination back together. But on the hot one I did fill in the gap at the bottom with the lamination stack pices from the original.

On the second unit I just left the stack out and it runs very cool with very good output.

These transformers have a 1/4" hole all the way through the lamination at each corner. I used bolts, nut and metal brackts to secure the 2 seperated pices back together rather then welding.

This worked very well but the heat culprit was the lamination filler.

These were transformers from 1 KW ovens. My clampon AC amp meter showed about 7 amps into the rectifier.

I'm very happy with the results.

                           JK TAS Jerry

[Ungrounded Lightning Rod]

In these last 2 transformers I did not weld the lamination back together. But on the hot one I did fill in the gap at the bottom with the lamination stack pices from the original.

How did you orient them.

You need to orient them so the magnetic field enters and leaves through the edges.  If you position them so it enters and/or leaves through a face you'll get a lot of eddy currents that heat it up.

[joestue]

It isn't so much the Lamination welding as it is the flux density and hysteresis loss.

Of the several microwave transformers i have rewound, the flux density was 1 to 1.1 million lines/square inch.

I'm using the 1900 era C.G.S units, flux=(E*10^8)/(4.44*hz*turns).

Incidentally that figure is 2 to 5 times times the density found in isolation transformers.

a good source for a transformer iron is those pc backup power supplies (UPS), most manufactures alternate the E cores and do not weld them.