Update on 'transformer question'

[wildbill hickup]

Thanks to everyone for your ideas. Well here it is 120VAC in 13.85VAC twin outputs and I didn't even wind up in the morgue.

I checked out all the links you folks gave me and set down last night with a chisle and hammer. Boy there is alot of wire on that secondary. I ran a test winding of about 4' (8 turns) and wound up with a little over 5V, unwound and cut moe wire thought I had enough for 20 but only got 17 (i prayed I wasn't short) it took awhile to get that double strand of 14ga romex (I know it's not the best but it's the only thing I had handy) on there. Hook up to the meter and was pleasently surprised 13.85-86VAC. Talk about dumb luck.

According to what I read at one of the suggested sites this shiould be capable af 10-15 amps. I still need to scrounge up a couple of bridge rectifiers 25A i figure will do the trick.

Boy now I got to go the the junk yard and find more microwaves. Nextime I'll probable use winding wire and go for a few more turns, but for now I've got something to play with. Found a circuit for controling chage rate as well on one of those sites looks pretty easy to build.

Thanx again to all

Wildbill

[wpowokal]

Wildbill, don't forget that when converting by full bridge from AC>DC volts are 1.4X AC.

Also remember I squared R losses in the transformer windings, they can heat up quite a bit. I have found that @ 25A into a 24V system they get ouchy hot, 15 amps is much more reasonable.

This might help

http://www.chantronics.com.au/Data/Transformers/transformers.htm

allan down under

[wildbill hickup]

Thanx for the info Allen,

>>Wildbill, don't forget that when converting by full bridge from AC>DC volts are 1.4X AC.

Lets see thats 19.39 that seems to be just about right (a little high) for charging 12volts right? This opperation will only be run for about an hour maybe two each day, and it will be monitored. This is deffinatly more of an experiment than anything else.

As far as temps go the transformer will be in my unheated dirt floor basement (about 50F yearround). Also let me see if I have this straight the amperage is controled by the size of the wire on the output side correct?? So even if the batts were very low the output would still only be the max of the wire size correct???I know it must also have to do with the purity(condutivity of the wire)this is just a rough interpretation.

Thanx for your time on this.

Wildbill

[wpowokal]

Wild bill, lets answer this backwards.

Use enameled winding wire, you are not going to need many turns so there will be plenty of room. I use multipul strands, much easier to wind and get looking neat.

Refer to this site for current ratings for a given wire size,

http://www.powerstream.com/Wire_Size.htm

For low batteries the current is limited by a combination of winding wire resistance but mostly the voltage, this is where to much volts and therefore amps,quickly overheats the winding. (remember volts is equal to pressure in water while amps is equal to flow)

I believe you will need close to 15-17 turns, based on your first post you have an AC volts/turn of 0.81, so 15 turns gives you 12.15V AC. DC 15.8V (12.15V AC X 1.4 - 1.2V( bdidge diodes) which should be adequate. The benefit of matching the volts to your ideal finish volts 15.5V DC, is the current should reduce to a trickle when the battery is fully charged.

So taking some voltage losses in the windings I would wind two strands of #18 gauge for 15 turns. Bring a loop out, do another winding, bring a loop out then another, finishing on the 17th. If you need more just soilder the ends and put on more windings. You will have plenty of room so wind three if you wish, the windings will run cooler.

 Now each of these loops sticks up the side of the coil forming a tapping point giving you some choice allowing you to tune the output current.

Please wind them at once, if you wind seperatly be very sure the number of turns are equal, and wound the same direction.

The temperature of the transformer in operation is predomintly from heating in the windings, yes ambient does make a difference but not as much. It does not want to be enclosed in an unvented case, but clearly safetly enclosed.

For the purists yes there are more factors to take into account in transformer design but not in this case.

allan down under