DPDT Relay Max Current Draw

[Triton]

Hey every one!

I have the DPDT relay control system (as described in http://www.homebuiltrovs.com/howtorelays.html) for my ROV but have not yet tested it under real conditions.
I have already bought the JQX-115F (http://pdf1.alldatasheet.com/datasheet- ... -115F.html) 12V coil, 8A DPDT relays. Yet, a professional guy here (I'm from Greece) assured me that these relays are not going to last for long (no more than 100 On/Off operations) with the current my motors draw (approx. 4.5Amps).
Does anyone know something on this?
What should I expect from these relays?

Thanks in advance.

[bikerbones1968]

Hi Triton, I read the data sheet for these relays. The physical contacts are rated for 10A @ 24VDC. Running a lower voltage across the contacts the current rating will be less than the rated 10A. I have no idea how much lower the rating would be on 12 VDC. I still can't see how or why they would only be good for so few of cycles even with lower load voltages. If you can find another supplier for DPDT relays with higher current rating at 12VDC you might be better off just the same. Personally if I were soucing relays I would use ones rated way higher than your maximum loads anyway. Better safe than sorry later.

[Triton]

Thanks BikerBones,

the problem is that there are not such DPDT mini relays at 12V with more than 10A rating (until now I have been able to find only 8A).
I have serious difficulties to find any different type of DPDT relay with higher rating in the Greek market but I'll do some searching
in the European market.
Anyway, I'll keep in mind your advise and see what I can do. Since I have already bought everything, I think I'll give it a try and see how it behaves under real conditions and higher depths (where currents would be higher).
I'll try to inform the forum when I'll have any results.

[bikerbones1968]

Your welcome, and you may never have any issues with the relays you have. Real world applications will tell the tale. I gather you dont have enough room for ice cube relays?

[Triton]

Hi BikerBones,


I actually have enough available room for ice cube relays, but still I haven't find any rated for more than 10A.
Is there any difference between the ice-cube relays and the mini-relays, so we would expect the ice-cubes to last longer?

[bikerbones1968]

They are physically larger and likely more robust. I have seen them with 15 amp 12vdc rated contacts. I believe they were Siemens.

[Triton]

Thanks again Bikerbones.
I'll keep looking and see if something comes up.

[thegadgetguy]

Most likely the relays you showed would work fine. I've been running mini H-Bridge relays for a few years now, rated to 10 amps, and they have worked flawlessly with up to a 5 amp load. Ironically enough, I had one of the ice cube ones melt in the same application! Anyway, a bigger safety margin is better, so go for larger ones if you can. If not, you should still be okay.

[Triton]

Thanks for the positive feedback thegadgetguy!
I was glad to hear that other people have tried succesfully something similar.
My first try with these relays on the ROV worked fine but not for long as the relays were not potted in wax or something similar.
I actually tried to use two plastic boxes to seal the control box: A small that contained the relays and a bigger one, in which I put the small box. The space between the two boxes (approx 1/2'' around the small box) was filled with wax.
I did this in order to be able to change a broken relay.
As it was proved, I did something wrong in the construction and water find its way in, at 10m depth (at the 2nd try!).
After this failure I decided not to try this sealing method again, and pot the relays in a 'liquid glass' material which I have tried to seal lights and has worked perfectly.
In this case though, if something is broken it can't be fixed but should be changed entirely.
I'm planning though, to pot the relays for each motor separetely in order to minimize the damage if just one relay is broken.
This way I'll have to change only to relays instead of 6.