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24V Transformer burning on Noritsu 3501

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Hi friends.
May anyone help please. AC24V Transformer for replenisher pumps is burnt on Noritsu 3501. I replace it and it works for 1 day then is burnt again. I replaced 2nd time and it works 1& a half days it is burnt again. What could be problem causing this?

 

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The input to the transformer is set on the wrong tapping.

For example you have 240V going in to the 200V tapping

The other cause is the 24VAC output is being shorted out, check the cables are not damaged and shorting to the machine chassis.

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Thank you for the reply Dave. Well I checked the input was connected to 240V tapping which is also shown on the manual. I tested pumps individually for short circuit & there is no short circuit . 

When I connect pumps 1 by 1 direct to transformer they are all rotating very well. Transformer does not burn instantly, machine can work for a day or so then burn later. 

Can the processor relay Pcb input voltage fluctuate causing transformer burning? Can processor i/o control circuit section be the one causing this problem. How best can I check these? 

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Thank you for the reply Dave. Well I checked the input was connected to 240V tapping which is also shown on the manual. I tested pumps individually for short circuit & there is no short circuit . 

When I connect pumps 1 by 1 direct to transformer they are all rotating very well. Transformer does not burn instantly, machine can work for a day or so then burn later. 

Can the processor relay Pcb input voltage fluctuate causing transformer burning? Can processor i/o control circuit section be the one causing this problem. How best can I check these? 

Sorry 220V input tap

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It's a very simple circuit, AC mains goes into the transformer and 24VAC comes out, The Processor relay PCB cannot alter the voltage going into the transformer, the voltage comes directly from your electricity supply. Measure the voltage coming in and check it is not above the transformer input voltage.

The Processor I/O PCB simply switches the AC24V to each pump with solid state relays, I can't see how it can cause the transformer to burn out.

You need to check all the wiring from the processor control PCB to the pumps, maybe one of the wires is shorted to the chassis earth, a wire trapped under a screw for example.

The only thing I can suggest is to put the tapping on to 240 instead of 220 to give a bit more leeway.

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Did you use original transformer, or just used transformer, which you found in local shop? If it is not original then you can't change input voltage. Original transformer has 5 inputs ( 200V, 208V, 220V, 230V, 240V ) and not original usually has only one.

Can test transformer before instillation on minilab. To secondary connect few 24V bulbs and primary connect to mains.

How your minilab is connected? If 4 wires then check "neutral" wire connection. If it has loose connection ( in your wall socket, distribution box and etc ) then transformer input instead 220V get 380V and will be burned.

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since Fototech can change a few times the transformerS make me feel they are of course not original ones. . . i would guess the local transformer copper wires are VERY thin... current rating too low.

once replenishment cycle starts,,, all replenish pumps work starting working at the same times,,  doing damage to the transformer ..   my best guess

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They are the original. I have found out that one of the replenisher pumps cable was not nicely tapped on the wire join so I am sure it was getting in contact with machine body. Problem is solved, thank you all for your contributions. 

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