DPDT Relays

[AHarris]

Hello,
I am buying some relays for my ROV however I am getting awfully confused with what I am looking at.
When searching on, rapidonline.com, I came accross hundreds of different types which all look the same but I am guessing do completely different things.

What sort of thing should I be looking for? Is it literally a DPDT relay or would something like:

PCB Relay
DPCO Relay
DC Power Relay
Subminiture PCB DPDT Relay

Would these sort of things do? SPDT was the most common one that I found, but is it the same as a DPDT relay as used by so many others on the ROV forum?

[thegadgetguy]

A dpdt is basically two spst relays connected together. If you want forward/reverse control, you'll need two dpdt relays coupled together to make an H-bridge. You would need two for every thruster. They actually sell H-bridge relays, which are sort of like two dpdt relays in one enclosure. They're nice because they are smaller and there is a little less wiring.

Good Luck!

[thegadgetguy]

Here is an example of a relay that might work:

http://www.allelectronics.com/make-a-st ... LAY/1.html

What voltage is your control circuit running on? And what type of thrusters are you using?

[AHarris]

For the thrusters, I am most likely going to go for three "Rule 360GPH Bilge Pump" motors which are 12Volts and approximately 3 Amperes in Air.
I may however look into rudders and use a servo to operate that, but this is something which certainly isn't common so I may not go for it.

The other issue I have is that I don't particullarly want to order from America as I would then need to pay not only for shipping but also import/export tax, mooring tax and a load of other wierd taxes that noone understands. I live on a tiny island which means we have very little in terms of electrical, plumbing and other shops which would sell the stuff which you would usually find in an ROV.
For this reason I may need to go for something other than a DPDT or H-Bridge relay if I cannot find one from within the UK which is of reasonable price, any other ideas how I can do this without having a massive battery to reduce voltage drop or a super thick tether?

[thegadgetguy]

Do you have an autoparts store?

[AHarris]

A couple of garages, why?
Would an "Automotive Relay" be the same as a DPDT relay?

[derelicte]

you probably want to avoid relays with pcb in the description. these are meant for soldering on to a printed circuit board (pcb) and will have small, thin leads which will be difficult to work with.

unless you are very good at soldering, you want some automotive type relays with big lugs that are easy to work with.

[AHarris]

Yes, I ordered some a while ago and found it impossible to wire, it was smaller than a coin and I therefore am looking for another, however the only big ones seem to be of a different type such as an SPDT relay.

Do you think I could use a "breadboard" and then just glue the bits in place?

Thanks for all the help to all of you for answering as well. It has been of great help!

[thegadgetguy]

Yes, those little relays are really hard to work with. I was just wondering about the auto stores/garages because the relays that control the electric windows on cars work pretty well. I found some H-Bridge ones that ran at 12 volts, 7 amps online that I used in my ROV, but you might be able to buy some at a garage or auto parts store. If they don't have them they might be able to order them. I'm not exactly sure how things work over there.

[derelicte]

maybe. breadboards don't usually make the best connections, and you might have intermittent problems.

also, there is no guarantee that the pins on the relay line up on breadboard.

breadboards are good for little experiments, but not much else.