Smoothing Capacitor

[apprentice87]

Hi All,

Advice needed!! I am building a hydraulic unit to power my tube bender. The solenoids on the hydraulic valves were i thought 24v ac.Turns out 24v dc....

Sooo, i have obtained a 400/24v control transformer and now i need to be able to obtain a dc output for the solenoids. Ok no worries, a full wave bridge rectifier is what is needed, so i ordered one like this. 

https://uk.rs-online.com/web/p/bridge-rectifiers/0193026/?searchTerm=193-026&relevancy-data=636F3D3126696E3D4931384E525353746F636B4E756D6265724D504E266C753D656E266D6D3D6D61746368616C6C26706D3D5E5C647B337D5B5C732D2F255C2E2C5D5C647B332C347D2426706F3D313426736E3D592673743D52535F53544F434B5F4E554D4245522677633D4E4F4E45267573743D3139332D30323626

Massively over specced i know, but at least you can bolt it to something and not have to solder a teeny little widgit to a pcb board!!

Anyway, do i need a smoothing capacitor????? At a wild guess, i would say no, as the inductance of the solenoid coils would help in this respect i would think [hope!!]. Secondly, when the solenoid coils are switched off, there is going to be a big surge of back EMF from the things, do i need to take any precautions to stop this surge from buggering up the bridge rectifier???

Solenoid coils are 24V 1.23A dc so that is about 30 watt. Just as well i ordered a 40 VA transformer then!!!

What say you all???

john...

 

[Lurch]

You'd probably get away without one, just bear in mind that a capacitor will give you about 36V on the output of the rectifier so you need to factor that into your control circuit.

What solenoids are they? Probably don't need anything to clamp the input but who knows.

 

[Sidewinder]

I would use a smoothing cap personally.

 

[apprentice87]

Thanks for that. No idea what solenoids, they just control a drectional control valve much like. [but not the same as] this one http://www.ebay.co.uk/itm/311023298288?_trksid=p2060353.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

The coild are 24v 1.23A, that is all i know.....

john..

Hi Paul,

Any idea what value???

john..

 

[Sidewinder]

You'd have to work it out John, I can't tonight, sorry, I am sorting out for a trip tomorrow for 2 days.

If no-one else does, then I'll look later in the week, I'm sure that there are others that can help you.

 

[OnOff]

Erm.........would a decent single phase in / 24vdc out psu not do you for the control side? Say 3A? 

Together with a chunky EMF filter of course...............

 

[apprentice87]

Hi Canoe, Only the one...

john..

 

[bluetobits]

Hi All,

Advice needed!! I am building a hydraulic unit to power my tube bender. The solenoids on the hydraulic valves were i thought 24v ac.Turns out 24v dc....

Sooo, i have obtained a 400/24v control transformer and now i need to be able to obtain a dc output for the solenoids. Ok no worries, a full wave bridge rectifier is what is needed, so i ordered one like this. 

https://uk.rs-online.com/web/p/bridge-rectifiers/0193026/?searchTerm=193-026&relevancy-data=636F3D3126696E3D4931384E525353746F636B4E756D6265724D504E266C753D656E266D6D3D6D61746368616C6C26706D3D5E5C647B337D5B5C732D2F255C2E2C5D5C647B332C347D2426706F3D313426736E3D592673743D52535F53544F434B5F4E554D4245522677633D4E4F4E45267573743D3139332D30323626

Massively over specced i know, but at least you can bolt it to something and not have to solder a teeny little widgit to a pcb board!!

Anyway, do i need a smoothing capacitor????? At a wild guess, i would say no, as the inductance of the solenoid coils would help in this respect i would think [hope!!]. Secondly, when the solenoid coils are switched off, there is going to be a big surge of back EMF from the things, do i need to take any precautions to stop this surge from buggering up the bridge rectifier???

Solenoid coils are 24V 1.23A dc so that is about 30 watt. Just as well i ordered a 40 VA transformer then!!!

What say you all???

john...

I might be wrong but isn't this where you need a flyback diode? 

 

[apprentice87]

What about a varistor across the coils?? would this help the back emf?? again, i have no idea which one i would need...

john..

 

[Lurch]

On the capacitor front I was going to suggest 10-22000uF but err more to the lower end of the scale. The back EMF I wouldn't have thought would be an issue, it's not something you would normally see across a DC solenoid valve like that. You could stick some diodes across it just to be safe if they are some unbranded Chinese randoms.

 

[apprentice87]

Thanks for that!! So you think i need, say, a 10,000uF cap.. will go with that one then, what type?? presumably an electrolytic one? What diode would be best  if i wanted to use one?? an 1n4007 type thing?? Not much [no!] experience with this sort of thing??

john...

 

[Tony S]

I had the same problem a while back, railway points of all things.

Tiefenbach GmbH wanted £1500 for a new control unit. The hydraulic cylinders and valves were OK so I built my own control panel and chucked the original in the skip.

Phoned the valve manufacturers, replacement 110V AC coils £10 each.

Got to be worth a phone call or e-mail.

 

[apprentice87]

Hi everyone!!!

Thanks for all the brilliant advice!!!!!

Due to being daft and rushing out and buying all kinds of stuff before i discovered that the solenoids were DC and not AC [teach me to read it properly!] I think i will have to try to make the best of what i have got...

1 x TP contactor with 24v AC coil

1 x overload relay

1 x 40va 400/230/24v control transformer

and now..

1 x bridge rectifier

First thing i was worried about was the back emf from the solenoids. Well, the rectifier has a peak reverse voltage of 1.6kV and a repetitive peak reverse voltage of 1.2kV..

Is everyone agreed that i can forget all about back emf, as, at the levels i will see [i presume], it will not make a blind bit of difference to the rectifier, which will i presume [see below] block them/it?? from reaching the transformer..????

Next, arcing when i open the control switch....

These are rated at 16A but then again i do not know what the arc will be like. I could put a capacitor across the switches, but what if i did the switching on the AC side, would the rectifier short out the back emf and hence the arc???

john...

 

[OnOff]

How about a nice (free :lol: ),chunky 24VDC, 1.6A PSU? IEC mains plug in and long lead out:





Think I've also got a cased, home built 24VDC psu based on the L200 chip. Good for 2A from memory...........question is what shed's it in?

Also found a 100VA 415/24-0-24 trannie and 48VAC contactors. Then a 96VA 400/42 and again 42VAC contactors.

 
 
 

 

[Lurch]

First thing i was worried about was the back emf from the solenoids. Well, the rectifier has a peak reverse voltage of 1.6kV and a repetitive peak reverse voltage of 1.2kV..

Is everyone agreed that i can forget all about back emf, as, at the levels i will see [i presume], it will not make a blind bit of difference to the rectifier, which will i presume [see below] block them/it?? from reaching the transformer..????

Next, arcing when i open the control switch....

These are rated at 16A but then again i do not know what the arc will be like. I could put a capacitor across the switches, but what if i did the switching on the AC side, would the rectifier short out the back emf and hence the arc???

The back EMF diodes probably won't be needed, I would imagine if they are required the instructions for the solenoids would say so. Wouldn't hurt to put some in if you wanted. The switches should be fine for operating the DC valves, I've never had a problem doing it in the past with standard 16A contact blocks on control panel switches, again unless the solenoid instructions mention anything then they should be OK.

 

[apprentice87]

Hi OnOff,

Just managed to retake the computer from the other half!!! Yes!! free electrical components would be very useful!! Are you sure?? PM me!!

john...

 

[Sidewinder]

The freewheeling diodes are not there for the benefit of the valves, they are to protect the switching devices, hence why they should always be fitted to say plc controlled solenoids, in fact any dc solenoid valve where the system is required to exhibit long term reliability. They should also be fitted to contactor coils when plc switched, or again if long term reliability is needed .

 

[apprentice87]

Hi Paul, Yes, i am definitely going to fit some of them. I am going to get 1N5408 ones, as i think they will be more suitable than the 1N4007 ones. Have not decided yet whether to fit a resistor in series with them yet though, think i will...

john...