high power supply

R!f@@

Joined Apr 2, 2009
9,682
I don't get it.

If you are rewinding them. I like to know how you went about it.

My circuit works and I have the current limit schema, I haven't uploaded it cause it is still a rough sketch.

for ur specs u need a lower secondary voltage. The core saturates when it is overloaded and this will reduce output.

To get higher amps u can parallel the windings. I believe u are unwinding the secondary and reducing the turns to get lover voltage.

Are u using the same unwounded wires to rewind it ?
 

Thread Starter

spankey666

Joined Nov 30, 2011
91
I have used same wire, wound on top of existing windings, unloaded voltage + 120v. loaded 90v both windings
removed second winding (to go back to where i started ) all ok ??
unwound all secondaries, re-wound to your spec with thinner gauge wire, high voltage once again ??, so just for kicks, i rewound again with thinner gauge, but this time paralleled the wire , high voltage once again from both windings. doesnt make sense. but a single winding of either gauge is ok even fully loaded.
it takes hours to rewind and re-assemble :(

if you would please let me have the cc part so i can get an order together and hopefully get something made by the weekend. :)
one point, the darlington pair switching the main transistors is an unknown component, i cannot even find a data sheet to cross reference an equivalent ??
 

R!f@@

Joined Apr 2, 2009
9,682
There is formula to wind mains transformers, but for this u need the Primary no. of turns.

Second, the winding must be tight. Loose windings cause problems.

Third, what u say is confusing.

Did u take apart the lamination ?
How are u keeping the lamination from vibrating during the test phace ?

Keep in mind the Voltage difference must be 5% from that of unloaded to loaded voltage. Any more difference means u are overloading the transformer.

Do you have picture of ur work
 

Thread Starter

spankey666

Joined Nov 30, 2011
91
I started off with 220v pri, 110 sec (stamped on the side figures)
the transformer is an E core type, with the top row of laminates welded down the sides. i machine the weld in a V to remove, and then re-weld each time for testing.

using the wiki equation,
started off with 108 turns secondary (110v) so pretty much 1v per turn.
using the formula equates to 216 primary turns
i have been winding 23 turns each time .
and yes i did the centre tap as you requested, this is when it started to go wrong LOL
it may just be that with all this winding and unwinding, the wire is getting distorted and not winding so tightly it is looking a little baggy although ive been using a lathe for turning so that i can get good tautness.
ive just been down the local motor re-wind shop, but the bloke i need to speak to isnt there until the morning, so i'll show him whats happening and get his advice and .pick up some fresh wire.
in the mean time, i need to get the circuitry sorted, i will feel better once ive actually started to make some progress LOL
so for simplicity (and costing ) i'll stick to your design inc output transistors, 12 of these are half the price of 6 of the ones i mentioned.
its just the BD727 i need to find a replacement for, and the CC part so i can get the bits ordered. at least then i'm commited and all of this googling and daft ideas about pwm and switching will stop LOL
 

Thread Starter

spankey666

Joined Nov 30, 2011
91
problem found............
my digital voltmeter is reading 136v when connected to 24vdc
DOH !!!!!!!
spent days chasing my tail trying to work out whats going on !!!!
 

R!f@@

Joined Apr 2, 2009
9,682
Ok...I am not been harsh but I cannot help it.

"Dummy" :D


{ed}
Ok... so I suggest u get some fresh wire but twice the size.
I will do some figures.

Vs = Ns/Np X Vp

For 34VDC output in CT config needs ≈ 53VAC ( 5% increased to allow for load drop ) ≈ 26.5 - 0 - 26.5 VAC.

Using the above formula and 216 for Np

Ns = 53 / 220 X 216 = 53 turns for secondary ( decimal rounded )

So now u need to wind 27 turns first. Take out some wire for the CT connection ( loop the coi ) and continue another 27 turn.

Using thicker wire than before wind two winding if you can .
you will than have two secondary windings of equal voltage.

Then u can parallel the two winding or series them if desired.

note


U have figure out if u can wind using thicker coil. If you can't, you can wire two windings of the same sized wire used originally.

I say this because u have a 110VAC. so basically it's 110/2 = 55VAC.

It is possible using same size wire.
I doubt thicker wires cane be wounded.

Use varnish or those stuff used to hold the coil in place. Wound tightly.
Use cable tight to hold the coil before u immerse the coil into glue ( varnish or whatever).

Immerse it completely and dry it in the sun.
After that insert the core.
 
Last edited:

Thread Starter

spankey666

Joined Nov 30, 2011
91
hahaha point taken :)
do you test your meter before every use ? does anyone ?? its relatively new and the fault seems to be intermittent .
not something i would expect to happen . anyways, i'll take it back tomorrow as its still under warranty.
 

Thread Starter

spankey666

Joined Nov 30, 2011
91
transformer re-wound, I took the bobbin to the local re-winders to buy the wire, and they wound it for me FOC... inc sleeving , lacquering etc, just paid for the wire . result :)
so now ive started bolting bits together, and found a rather nice pc case in the shed to assemble in.
so now onto the issue with heat, or should i say cooling of the transistor bank.
ive got various lengths of ally heat sinks but space inside the box is going to be limited, and ducting the air supply will be even more tricky.
so water cooling looks like the best option.
i was thinking that 4mm copper plate between e pipes like this
http://www.vonslatt.com/images/cc11-sink1.jpg
and seeing as the transistor collectors are all connected, the heatsink could be the bus bar.
my version

the heat can now be pumped outside the workshop, which at the moment i could do with inside, but in the summer it will be unbearable .the outside rad can be a car rad with 12v fan already fitted.
if anyone has any experience with this type of cooling please chime in and let me know of any pitfalls i might experience.
Thanks for everything so far
 

R!f@@

Joined Apr 2, 2009
9,682
Did u do any voltage and current measurements on the transformer.

I need actual specs. Loaded to unloaded voltage. It's important u know..

As for the water cooling, that won't do. U need to use copper pipes Soldered on to copper base which will give excellent results.

Have u seen any water cooling methods.

And see if you can find a copper sheet block for the transistors. This will be awesome. And keep in mind that the sink needs to be isolated from the rest of the chassis.

U should not water get into contact with live parts.
 

Thread Starter

spankey666

Joined Nov 30, 2011
91
that was a cross section pic, water will be pumped through the pipes top and bottom, plate is 4mm copper, all will be brazed.
i will sort out some figures tomorrow, i'll try to run full load, and measure temp rises etc in core to check my fan cooling.
 

R!f@@

Joined Apr 2, 2009
9,682
Remember to keep the sink and radiator insulated from the chassis.

U will have RAW DC all through out. Run Copper pipes from sink to Radiator.

Have enough space to mount the emitter resistors as well and the current shunt if u are using the latest heat sink mountable ones.

And when drilling Make sure u have enough space from edge to the hole where u will have to use eye lugs to connect +B wire to the Base plate.

Never try to solder heavy duty wires. Always uses lugs to bolt the wire to copper or metal.

When measuring transformer voltage and current.
I will need the unloaded AC secondary voltage details with loaded current and voltage. Loading should be calculated by measuring unloaded voltage.

It should drop by max 5% of the unloaded VAC. This will be ur continues transformer secondary current. U cannot exceed this value.

Have u decide anything on the filter caps yet.

I suggest that u make copper plates to mount the caps to cope with heavy current. I presume the caps will have screws as connection terminals.

By the way, order some arctic silver heatsink compound. U won't regret it.
 

Thread Starter

spankey666

Joined Nov 30, 2011
91
i eventually have some raw figures. the joys of buying cheap ammeters from china via ebay :(
all i have is transformer ,bridge rectifier and shunt for ammeter connected.
using 1 set of windings, as doubling them up amps go over 100 (the limit of my ammeter)
unloaded :
28.25V ac - 33.6V dc
loaded pulling around 54amps 23.5V dc
 

R!f@@

Joined Apr 2, 2009
9,682
I was wondering where u were.

Maximum regulation u can achieve is 23.5 - 5 = 18.5VDC @ 54 Amps.

Are u happy with that figure.

If not u need another transformer in parallel. with that I guess u can go up to 27VDC more than 70 amps.
 

Thread Starter

spankey666

Joined Nov 30, 2011
91
i have had the transformer wound as you suggested with 2 identical windings, so i have another set to parallel up :) i could not measure the output current as it was beyond the 100a range of my meter :( i can measure the voltage though and report back :)
 

R!f@@

Joined Apr 2, 2009
9,682
Hey wait....

Figures are not as I suggested. I said no load voltage should be 53VAC. as per post #67

What happened. Did I screw up the Ns figure or the one who wound it screwed up ?

Tell me this, how many terminals are there in the secondary. It should be 3 not 2.

If 2 is there, u guys screwed it up.
 

Thread Starter

spankey666

Joined Nov 30, 2011
91
it was wound 27 turns, pull a bit extra wire out then another 27 turns. the centre tap ive cut so i have 4 wires . ive only tested 1 set of windings for the above reasons :)
i will re-check figures , tested with a brand new multi meter, i will check that as well just in case
 
Top