solid state relays

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Old 09-07-11, 12:11 AM
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solid state relays

hi i have 4 X 12 volt batterys conected up to make 48 volts

im trying to find a solid state relay that i can use to reverse the polarity of the current to the motor

what type of solid state relay should i be looking for
i recently a 3 phase solid state relay off ebay that i cant get to switch the current when i input voltage to the coil to switch . . . .im not sure if there are AC relays and DC relays ...........
any help be apreciated : )
thanks
 
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Old 09-07-11, 07:49 AM
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Why not buy a motor reversing switch? It does all the work for you. OF course you are in the UK and you didn't say what you would be using this 48 volt supply on, so we are at somewhat of a handicap not knowing the full picture.
 
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Old 09-07-11, 09:21 AM
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Solid state relays are made in both AC and DC models and no, they are not interchangeable. Since you state you have a 3-phase relay I am pretty sure it is an AC relay and it won't work on DC.

Also, while there are exceptions, most common solid state relays are going to be normally open models and finding a SS relay that has multiple poles along with being "double throw" is likely an exercise in futility.
 
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Old 09-07-11, 09:42 AM
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ah i think furd has hit nail on the head .
these are the relays i bought
eBay - The UK's Online Marketplace

and i wanted it to control the reverse polarity of 48 volt motors with relays
because i plan to have a computer controled relay card operate the ssr`s
 
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Old 09-08-11, 04:24 AM
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DC Solid state relay

Hi Rattled_Cage

The relays you purchased are indeed AC relays. This relay has a 3-32VDC input (coil in conventional relay) that will then switch an AC current through the terminals.
If you wish to drive a DC motor then you would need a DC SSR. If you wish to switch motor direction then you are going to need a H-Bridge configuration of 4 such relays. Depending on the current your motor will be drawing there are few "ready made" H-Bridges .
Something like this may come into question
Crydom - Product Catalog
or
http://www.crydom.com/en/Products/Catalog/d_p4_r.pdf

I warn you now though that these will not exactly be cheap.

Hope this helps.
Regards
Stewart
 
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Old 09-08-11, 04:31 AM
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A double-pole double-throw mechanical relay will do this, but it will be on all the time in one direction or the other. Connect the motor to the armature contacts. Connect +v and 0v to the NC outputs, and reverse the connection for the NO outputs. (Or vice versa.)

You would need a second relay to stop the motor. It would connect between the power source and the other relay's armature.

Also, I strongly recommend buffer relays between the computer and the coils of the load-carrying relays. This is where you could use a solid state relay.
 
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