230vAC - 12vdc problems?

[Diver300]

You could try reducing the number of secondary turns on the transformer.

The secondary turns will be very thick wire, and they will be outside of the primary windings, so it isn't all that difficult to do.

 

[dannix]

mvs sarma, We have a 230v supply here in the UK so I can not supply it with 110v, the primary windings are already wired in series.
THere is little information with the dc convertor, there is some pots for output voltage adj and battery low voltage disconnect setting, other than that there is little to see, an inductor, several caps and what look like SMD mosfets or similar. There is a hight res pic here: http://www.mpegbox.com/DSX12VD.html the DSX12V is the same but with less features, it has a better manual and in that it says: Input Protection Clamp 24V so unless peak is just hitting it since the transformer is under no little load the output voltage is higher than stated which compounds the problem.

I will try with a resistor on the input, might be an idea to order a new transformer at 12v out and try that. I could use this transformer for a desktop supply with a few more bits.

Regards,


Driver300, your right it could work, but I only just got this transformer, don't really want to rip it to bits

 

[mvs sarma]

mvs sarma, We have a 230v supply here in the UK so I can not supply it with 110v, the primary windings are already wired in series.
THere is little information with the dc convertor, there is some pots for output voltage adj and battery low voltage disconnect setting,.................

Sorry Dannix, I missed it. You have in fact indicated that you are working at 230V in the first post itself. Of course, no indication that you are in UK.

OK. please try inserting a 100Watt bulb in series to Primary for a short while for observation. By some trick i wanted to supply a voltage of around 15V to the DC-DC converter, from the Transformer you have.

In fact the transformers of the olden days used to have taping in the primary section to enable input voltage setting.now we need some rectified supply near 15V for test purpose. Perhaps you can connect a 7915 with some heat sink, and get 15V.

However it is only for test, and not for real load.Let

 

[dannix]

I was hoping pwm would have worked for that but it didn't. I will try and get the voltage down one way or another prob a 7915

 

[mneary]

@dannix, you can help us (and in the end help yourself) by including your location in your profile.

 

[mvs sarma]

I was hoping pwm would have worked for that but it didn't. I will try and get the voltage down one way or another prob a 7915

It should be 7815 and not 7915. 79 series are negative regulators.

 

[dannix]

It should be 7815 and not 7915. 79 series are negative regulators.

Yeah I noticed when ordering, I work shifts so I have little time to test untill monday when I have 3 days to get this working. I am ordering supplies including a 12v transformer, It occured to me that if I have a load on the output of the dc-dc convertor it may stop the backfeed of the the onboard caps letting me put unsmoothed dc in. think its worth a try? I can try that tonight. Otherwise I need some supplies as I only have 7805's in my little stock (thats growing quickly)


@mneary I will update my profile

 

[dannix]

Right I have got a 9vac out transformer 100va this will give me the 10a max i require with a little extra (not as much as I would like but wont't be max'ed out much)

so by my calc thats 9vrms * 1.414 = 12.73
12.73 - 1.4 diode v drop = 11.33vdc at max current

in reality the transformer output voltage will be higher at the intended lighter loads, I guess about 10vac, which is 12.7vdc.

In both cases the DC-DC convertor will buck / boost it!

I will keep the 15vac 300va transformer for a desktop PSU, any recomended schematics that can take 15vac in and give variable 3-12vdc (give or take) out?

 

[electronic spark]

Sounds like it's shutting down on over voltage? (16V)

 

[mvs sarma]

Right I have got a 9vac out transformer 100va this will give me the 10a max i require with a little extra (not as much as I would like but wont't be max'ed out much)

so by my calc thats 9vrms * 1.414 = 12.73
12.73 - 1.4 diode v drop = 11.33vdc at max current

in reality the transformer output voltage will be higher at the intended lighter loads, I guess about 10vac, which is 12.7vdc.

In both cases the DC-DC convertor will buck / boost it!

I will keep the 15vac 300va transformer for a desktop PSU, any recomended schematics that can take 15vac in and give variable 3-12vdc (give or take) out?

Change the transformer and turn o , you would succeed.
the converter has buck&boost

 

[Diver300]

Driver300, your right it could work, but I only just got this transformer, don't really want to rip it to bits

I guessed that vandalism wasn't high on your list of priorites.

Here is a less permanent suggestion.

Firstly find the approximate volts per turn. to do that, feed the transformer with 230 V and measure the voltage on one turn. You can just feed one lead of your voltmeter through the center of the transformer, and short the probes together and that will show you the voltage.

Now devide 230 V by this and it will give you the number of turns on the primary. I expect about 1V per turn, so about 200 - 300 turns on the primary.

Now wind more turns around the transformer. If you add 10%, the output voltage will drop 10%. Just use some PVC insulated wire. It doesn't have to be neat.

You have to put the wires the right way round, so put a 60W bulb in series and check the voltage on the transformer and on the series combination of the transformer and the extra turns. The voltage on the transformer must be less than the voltage on the combination. If not, you have the extra windings the wrong way round.

Once you have the windings the correct way round, you can feed the combination directly from 230V.

Obviously, be carefull messing with 230V.

Good luck.

 

[dannix]

Driver300, good idea! I have some spare twin&earth perfect for this, I already took the earth out for something else, it's even the old black and red. I will give it a try.

I am ok with mains, used to work on industrial 3phase overhead cranes till I went into IT, im 16th eddition with no plans to take 17th, although amazing what you forget as time passes though!

 

[Diver300]

Single core flex might be easier to wind. You need to push the wire through the torroid once for each turn.

 

[mvs sarma]

Single core flex might be easier to wind. You need to push the wire through the toroid once for each turn.

Generally single core wire is used by the manufacturer and a flexible connecting end wire is provided for ease of termination.

you have to appreciate that winding direction is important and it should be same and in continuation of original, to be effective.

 

[dannix]

Good news, I replaced the 15vac transformer for a 9vac transformer and it is now working a treat, thank you everyone for your assistance, most appreciated!

 

[mvs sarma]

Good news, I replaced the 15vac transformer for a 9vac transformer and it is now working a treat, thank you everyone for your assistance, most appreciated!

Nice to know that you have a Realized project and not a dream project.

 

[dannix]

not quite, this is just one aspect but I am reaching the end, slowly.