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from the I&C department...
Relay Required
Engineering and workplace issues. topic
Posted by Anonymous on 2 July, 2004 - 12:05 am
I am looking for the following type of relay:
Contact rating: 125 VDC, 8 A, DPDT type.

Can anybody help pls?


Posted by Fred Townsend on 3 July, 2004 - 1:17 am
There is probably no more than 100,000 give or take 1000,000 relays that would meet your requirement. Why do you need help?

Fred Townsend


Posted by ANA on 7 July, 2004 - 10:21 am
No its not so simple....the problem is genuine. Please look at he voltage rating its 125VDC and its really hard to find any realy at this voltage rating for 8A of current. If it is AC voltage then i agree with you but not for DC.

I guess our friend might have to go for a contactor instead of realy and if cabinet space allows. In my recent project i was looking for 2A, 125VDC realy with continous duty and it was hard to find. Please check in Schneider AS series.

You can contact me on ana@iics-sa.com

i might be of some help or at least to discuss.


Posted by Dean Norton on 6 July, 2004 - 11:13 am
Give WAGO a call. Part number is 788-315.

1-800-DIN RAIL or 346-7245.

http://www.wago.com


Posted by Johnny Crab on 6 July, 2004 - 11:26 am
We've had failures of a "well-known" vendor's relays here on similar applications...in one case a large machine with a 500 hp motor stayed on when it should've shut down(relay did not open). Not pretty and lotsa damage caused by a few $$ relay. We replaced the questionable relays with these( http://catalog.weidmuller.com/asp/datasheet.asp?PN=991998 ) and have had good service so far(4 years, no failures). They are modular and DIN rail mount, Part Number 991998.


Posted by Meir Saggie on 6 July, 2004 - 2:17 pm
At this DC current and voltage levels, you'd rather look for a contactor. 110 VDC is substation control voltage level.

Meir


Posted by Matthew Hyatt on 7 July, 2004 - 9:55 am
Try out

http://www.newark.com, http://www.digikey.com, http://www.mouser.com

Geez, there are probably 10 to 20 relay manufactures I can count on one hand who have this type of relay available from stock.


Posted by Leigh on 9 July, 2004 - 3:55 am
When I saw this post, I assumed there were plenty as well, but if you read the data sheets properly, it's not so easy. The Wago 788-315 suggested by a contributor won't do it. (According to the data sheet, yes it will switch 8 amps, yes it will switch 125VDC, but it won't do 8amps at 125VDC, even with a resistive load and two contacts in series). In case I should ever need such a device myself, I wonder if the contributors who know of numerous examples would be kind enough to list the first ten or twenty part numbers they feel would be suitable. Personally, I think you're going to need a contactor, especially if the load is inductive and you need large number of ops.

Leigh


Posted by Curt Wuollet on 13 July, 2004 - 1:35 pm
These days a FET would probably be the best way. But I haven't seen many packaged solutions since they started discouraging mercury.

Regards
cww


Posted by Michael Griffin on 11 July, 2004 - 1:17 pm
I think you would need a DC contactor, which will probably have an arc chute. At above 24VDC (possibly in the 50-60 volt range?), the DC rating of most relays drops off drastically. The market for this type of application is very limited, so it can be difficult to get the detailed relay specs required to determine this. Fairly often, the relay manufacturer doesn't know, because they haven't tested that model under those conditions.

If you can switch the relay at zero current (e.g. by disabling the DC power supply electronically), then the relay doesn't have to make or break the DC current and you have a lot more options available.


On July 9, 2004 03:54, Leigh wrote: <clip>
> When I saw this post, I assumed there were plenty as well, but if you read
> the data sheets properly, it's not so easy. The Wago 788-315 suggested by a
> contributor won't do it. (According to the data sheet, yes it will switch 8
> amps, yes it will switch 125VDC, but it won't do 8amps at 125VDC, even with
> a resistive load and two contacts in series). In case I should ever need
> such a device myself, I wonder if the contributors who know of numerous
> examples would be kind enough to list the first ten or twenty part numbers
> they feel would be suitable. Personally, I think you're going to need a
> contactor, especially if the load is inductive and you need large number of
> ops.
<clip>

--

************************
Michael Griffin
London, Ont. Canada
************************


Posted by EST on 28 July, 2004 - 10:50 am
Good luck. As an engineer for a European manufacturer of relays and contactors, I felt obligated to research in a bit more depth. What I found is that there are different current ratings depending on the load. They are defined by IEC terms as DC-1, DC-3, DC-5, DC-12, DC-13, DC-14 (and likely others). Regardless, no relay we manufacturer meets your needs. The closest we get with a relay is 6 amps at 110VDC, 5 amps at 220VDC, and this requires placing 3 contacts in series.

For those recommending utilizing a contactor, remember the need for DPDT, meaning he (or she) needs normally open AND normally closed contacts. If that is truely a requirement, your field narrows.

Sorry I could not be more help. For those of you stating there are "1,000s" of relays out there, please let us all know ONE relay with two normally open and two normally closed (or two form C) contacts, each rated 8 amps at 125VDC. I, too, would like to know.

Thanks and good luck.

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