I have a new project which is a Tyre Balancer Machine

What's the other voltage regulator that is still on the board - a 7905 or a different voltage? And the value & voltage of the smaller electrolytic - that's not visible from that angle.

rjenkinsgb said:

What's the other voltage regulator that is still on the board - a 7905 or a different voltage? And the value & voltage of the smaller electrolytic - that's not visible from that angle.

Click to expand...

I was about to ask the same thing. One capacitor is labelled 25V 4700µF, and it numbers like that, a voltage and a capacitance, that is needed from the other capacitor.

With the regulator and the relays being 5 V, it's looking like the power supply is only used to create +/- 5 V, so a 9-0-9 V transformer would be what is needed.

You could also just get hold of a regulated +/-5 V supply, or even two 5 V regulated supplies, and wire them in, with the regulators removed from the board.

I will find out the information of the cap and the other semiconductor on the board.
the cap is 25 v. 2200 uf

Photo of board

It looks like the power supply is just +/- 5 V, with a bit more power available on the +5 V, probably to run the relays and maybe the display.

I suggest a 9 - 0 - 9 transformer. It will need the neutral of the three phase for just about all transfomers.

You could use one of these:-
https://uk.farnell.com/block/uste100-2x12/transformer-isolating-100va/dp/1177116
which is big and expensive but it will run directly from two of the three phases on 380 - 420 V with no problem.

That transformer has a 12 - 0 - 12 output voltage, which could make the regulators run hot. However, you can configure it for a higher voltage, and then when you run it on a lower voltage than it is configured for, the output voltage will be lower.

For instance, if you configured it for 600 V, and ran it on 420 V, the output would be about 12 x 420 / 600 = 8.4 V, which would be perfect for +/- 5 V supply.

You can always run transformers on a lower voltage than they are designed / configured for. The VA rating goes down when you do that, because the current rating stays the same. The transformer I linked to has a much larger VA rating than you need, so you would have no problems there.

If you run transformers on a larger voltage than they are designed for, they can get hot, as you found out.

can You work out the turns on a transformer by the resistance

What v transformer would you recommended With the information I have supplied.

Probably around 8-0-8 or 9-0-9, like I said many posts back & diver concurred.

But, you don't seem to have posted the info from the other voltage regulator yet? It's hidden behind the black multi-pin header in the photos above.

I will post the photo of the regular this will help I hope

OK, that is a 7905.

A transformer with an 8-0-8 or 9-0-9 secondary would be ideal, though a bit higher will also be OK, it will just mean the regulators run a bit hotter.
I'd not use higher that 12-0-12 though. One rated at 1A or so would easily be adequate.

As Diver said, you could use one with a somewhat higher primary tap than needed and under-run it to reduce the secondary in proportion.

I have purchased a trans former will this one do the job .

Gregory said:

I have purchased a trans former will this one do the job .

Click to expand...

That looks fine.

You must make sure that the supply isn't more than 240 V. You will need a neutral connection, not just the three phases. If you connect that transformer between two of the three phases, it will burn out.

You have to connect the 240 V to the correct winding. As far as I can tell, it will only have two wires, because there is only one voltage option for the input voltage, and the resistance between those two wires will be higher than the other windings, maybe 100 - 1000 Ohms. Having looked up that transformer, I think that it has wires for the 240 V connections and tags for the 0, 9 and 12 V, but check the resistance anyhow.

You have to work out which are the 9 V windings. It should be labelled. If not, they will be lower resistance than the 12 V ones. Alternatively, power up the transformer and measure the voltages.

The diagram that I found for that transformer shows two independent windings. http://www.soanar.com/images/ocw/1247500_400_300.jpg

It's not clear from that how you connect the secondary. You will need to supply power to the transformer to find out. First check that you can measure 9 - 10 V ac between the 0 and 9 V connections on each winding. Then turn off, and connect the 0 V connection on the first winding to the 9V connection on the second winding. Then turn back on and check that you have 18 - 20 V ac between the 9 V connection on the first winding and the 0 V connection on the second winding.

If not, turn off, remove the connection you made, and connect the 0 V connections on the two windings together. Then turn back on and check that you have 18 - 20 V ac between the two 9 V connections.

Whichever way gives you 18 - 20 V ac, you will have a common connection, and two wires are at 9 - 10 V ac from the common connection and they are 18 - 20 V ac from each other. That is how you leave it when connecting to the circuit board. The picture shows where the two 9 V connections and the common (0 V) connection go, as well as where the mains connections, L and N, connect.

The transformer has one side 0 and 9 volts with my multi meter
on the other side it has 0 and I get 9 volts with my multi meter
do I only have to solder one wire from the centre tap on the board to the 0 tab on the transformer
Or solder a another wirer on the board on the centre tap to the 0 tab on the transformer
could you give me a circuit digram please.

Can you send a photo of the connections on the transformer?

This is what you need to achieve. You need to join the two windings and that point needs to be wired to the centre tap point on the circuit board.

If you get around 0 V between the two ends of the windings, then one winding is the wrong way round. It doesn't matter which one you reverse, but you must get 18 V between the ends.

I have connected the transformer as per your circuit.
I have blue wires solder together.
the readings are in the photos . From 0 to 0 with power on.
Then from 0 to 9 volt both tabs on the transformer

If you would like other photos please ask.
If you are happy with the wiring I will go ahead and install the transformer.
Thank you

It's correct that you don't read any voltage with only one connection to each winding.

I can't see any markings to say which how the the directions of the windings relate to each other. Most transformers with two secondary winding have some indication. I was expecting something on your transformer or its data sheet, but I can't see anything.

If I call the windings A and B, you have 6 terminals, A0, A9, A12, B0, B9 and B12

Don't connect anything to A12 or B12.

Connect a A0 to B0.

Measure the voltage between A9 and B9

If that is about 18 V, you have the correct connection. The wire that joins A0 and B0 is your centre tap.

If the voltage between A9 and B9 is not about 18 V, disconnect the wire from A0 to B0. Connect a wire from A0 to B9. Measure the voltage from B0 to A9. If that is about 18 V, you now have the correct connections and the wire that joins A0 to B9 is you centre tap.

If neither arrangement gives 18 V, something has gone wrong.

Also I suggest you solder wires to A0, A9, B0 and B9 and take the other end of each of those wires to a terminal block, and do the measurements on the terminal block. It will be easier to make the connections and to perform the measurements on the terminal block, and you can do less soldering on the solder tags of the transformer. It's easy to damage the transformer if you keep on soldering and unsoldering wires.

I have connected the 0 wires together . The reading between the red white wirer and blue 0 is 9 volt
The reading between the red and blue 0 wires is 9 volts
The. Reading between Red White and red is .003 Volts Ac.
Does this help you out.

Transformer Info