Fwd/Reverse Motor Control using DPDT's?

[Pcolaboy]

Hi everyone...first post here.

My son and I are building a submersible ROV and I'm researching how to devise a simple motor control setup.

The ROV will be powered by a total of 3 12VDC motors that will draw up to 5amps each. Two motors mounted horizontally are used for forward/reverse and also for turning the vessel by alternately reversing direction on the motors. The third motor is mounted vertically and is for up/down only. 12V Power will be supplied from the surface via 100ft 12 or 14 gauge stranded wire. A 100ft CAT5 cable will also be brought down to the ROV for input to the relays from a control box where there will be a 9v battery.

I haven't nailed down exactly how the control box will be layed out or how I will perform input to the relays. I would like to use momentary on-off-on toggle switches if possible - one for left horizontal, one for right horizontal, and one for the vertical motor. Can these be used in conjunction with the relays? Better suggestion?

I've read from various sources that to achieve Forward/Reverse , I will need to use two DPDT's for each motor. Logically speaking, to move straight ahead both horizontal motors would be switched to 'forward', and to go straight backwards both would be switched to 'reverse'. For turning left, the right side motor would be switched to 'forward' and vise-versa for turning right.

My main question that I've been unable to find the answer for is, are there any other electrical components that will have to, or should be used on the ROV side of the circuit in conjunction with the relays. I'm not ready to dive into the world of using speed controllers, programmable interfaces, etc.

I'm sure that there are alot of gaps in my description of what I'm needing so please don't flame me too hard.

Thanks in advance,

Pcolaboy

 

[3v0]

Does this work for you?

On the surface use a SPST center off switch for each motor.
The switch will activate one of two relays (in the vehicle) connected to the motor.
Pushing the switch ahead will activate a normally open two pole relay that will cause the motor to run forward.
Pushing the switch back will activate a 2nd normally open 2 pole relay to run the motor backward. The supply/input side of this relay is wired opposite of the 1st relay.

Duplicate this setup for each of the three motors and you have it.

If this is not clear I can post a schematic.

 

[crutschow]

Here's the basic relay circuit to reverse a DC motor.

 

[Pcolaboy]

Thanks for the great information. A diagram of what you have in mind would be awesome. Of course, then there lies the problem that I honestly don't know how to read a true electrical diagram -YET.

Is there a layman's way you could diagram this including the 9v battery used for the control power?

At the risk of "wearing out my welcome" , I have a few other questions keeping in mind that I've never built a circuit in my life:
1. To protect the motors, should I use fuses downstream from the relays?
2. Is soldering the relays and connections to a proto board recommended?
3. Should heatsinks be used on the relay board? If so, do you have a recommendation?
4. Are there any other circuit components to consider on the relay board for regulation of the voltage/amps, etc?

Thanks again!!!

Scott

Does this work for you?

On the surface use a SPST center off switch for each motor.
The switch will activate one of two relays (in the vehicle) connected to the motor.
Pushing the switch ahead will activate a normally open two pole relay that will cause the motor to run forward.
Pushing the switch back will activate a 2nd normally open 2 pole relay to run the motor backward. The supply/input side of this relay is wired opposite of the 1st relay.

Duplicate this setup for each of the three motors and you have it.

If this is not clear I can post a schematic.

 

[3v0]

EDIT:
The schematic was not easy to read. See one a few post up.

 

[3v0]

Thanks for the great information. A diagram of what you have in mind would be awesome. Of course, then there lies the problem that I honestly don't know how to read a true electrical diagram -YET.

Is there a layman's way you could diagram this including the 9v battery used for the control power?

At the risk of "wearing out my welcome" , I have a few other questions keeping in mind that I've never built a circuit in my life:
1. To protect the motors, should I use fuses downstream from the relays?
Fuse goes between the + bat terminal.

2. Is soldering the relays and connections to a proto board recommended?
For this I would try to find relays with screw terminals. Crimp and solder terminals to the wires and screw them to the relays. Not a must. Others may not agree.

3. Should heatsinks be used on the relay board? If so, do you have a recommendation?
Not required for mechanical relays.

4. Are there any other circuit components to consider on the relay board for regulation of the voltage/amps, etc?
Not that I know of.

Thanks again!!!

Scott

.....................

 

[3v0]

Better schematic.

This is an easier to understand schematic of the same circuit.

When the switch S1 is in the center both relays are off.

When the switch S1 is up 2 provides power to 1 which activates relay K1.
K1 closes contacts S1 and K1 and the motor is powered -,+


When the switch S1 is down 2 provides power to 3 which activates relay K2.
K2 closes contacts S2 and K2 and the motor is powered +,-

That is all there is to it. Questions ?

 

[Pcolaboy]

That does make much more sense to me..thanks a ton! Did you happen to see the other questions I had in the previous reply?

Pcolaboy

 

[3v0]

Check the post following the one in which you asked the question. My answers are in bold.

 

[holdit]

sorry to butt in like this but i have a similar problem
i have 2 motors that i want to control individually eg:
M1 forward/backwards
M2 forward/backwards
(but either one could be on or off but none on when power is appiled to curciut)
with a 2 dpdt switch with a off postion is easy to do but the dpdt relays i have dont have a off but have another dpdt relay is there an easy way to wire this up as i have thought for a long time now by the way it will be controlled by a pic controlled relay board i built But i must only use 3 relays max
thanks i could start a new thread if required

 

[3v0]

but either one could be on or off but none on when power is appiled to curciut) with a 2 dpdt switch with a off postion is easy to do but the dpdt relays i have dont have a off but have another dpdt relay is there an easy way to wire this up as i have thought for a long time now by the way it will be controlled by a pic controlled relay board i built But i must only use 3 relays max

That is one long and difficult to understand chunk of text.

I think the circuit I provided below will do exactly what you want.

The control switch has a center off position. That will keep all motors off when power is applied. When the switch is moved to either side (throw) it will energize one of two relays. On relay runs the motor forward, the other backward.

Use as many of these as you have motors.

If you need a different setup please explain what you need in short clear sentances.

 

[Pcolaboy]

3VO,

Did I mention you are the man?

I've been shopping around for DPDT relays and I'm a bit unsure how to select one based on the various specifications.

Considering the following factors can you recommend what specifications to look for when selecting relays?
1. Each motor draws a minimum of 3A @ 12VDC and are rated to 5A @ 12VDC
2. 12V will be supplied from a 12V Deep Cycle Marine battery on 12 ga stranded wire at 100ft in length (obviously there's going to be some pretty decent voltage drop)
3. The control box circuit will be powered by a 9v battery and will travel down to the ROV on 100ft of CAT5e cable.

Having said all that, many of the relays I'm seeing online have a description of "12V DPDT Relay 5A" or "5V DPDT Relay 2A". If my control inputs are going to be less than 9V with output being around 10-11V which one would I choose? Does this make sense?

Thanks again for all the input!!!

Pcolaboy

 

[holdit]

ok sorry about that
relay 1 dpdt = motor 1 fwd/bck
relay 2 dpdt = motor 2 fwd/bck
relay 3 dpdt on off for ???? (motors ? relay? power? there is common/nc/no
i cant think how to wire relay 3 because there must be no power to motors when not energized but must still allow independent control of motors
sorry for long text

 

[3v0]

3VO,

Did I mention you are the man?

I've been shopping around for DPDT relays and I'm a bit unsure how to select one based on the various specifications.

Considering the following factors can you recommend what specifications to look for when selecting relays?
1. Each motor draws a minimum of 3A @ 12VDC and are rated to 5A @ 12VDC
2. 12V will be supplied from a 12V Deep Cycle Marine battery on 12 ga stranded wire at 100ft in length (obviously there's going to be some pretty decent voltage drop)
3. The control box circuit will be powered by a 9v battery and will travel down to the ROV on 100ft of CAT5e cable.

Having said all that, many of the relays I'm seeing online have a description of "12V DPDT Relay 5A" or "5V DPDT Relay 2A". If my control inputs are going to be less than 9V with output being around 10-11V which one would I choose? Does this make sense?

Thanks again for all the input!!!

Pcolaboy

Relay specs can be confusing. If only one voltage is listed it is for the voltage required to activate the coil. So you want to match the control battery voltage to the relay coil voltage. There is no reason to stick with 9V, 4 rechargeable C or D cells would work well with 5V relay and power the relays for a reasonable amount of time. (guessing here) I do not think the voltage drop over 100 feet will be much with good connections.

The contact current voltage is not clear to me. Some relays only give a current ratting for the contacts while other give a current and a voltage. Maybe and EE type could say more about that and if you need to add a cap to prolong the life of the contacts.

 

[3v0]

ok sorry about that
relay 1 dpdt = motor 1 fwd/bck
relay 2 dpdt = motor 2 fwd/bck
relay 3 dpdt on off for ???? (motors ? relay? power? there is common/nc/no
i cant think how to wire relay 3 because there must be no power to motors when not energized but must still allow independent control of motors
sorry for long text

Are you saying that the relay 1 and 2 could be on when power is applied? You want to use relay 3 to prevent power from flowing through 1 and 2 at power on time.

I am afraid that I still do not understand. Maybe if you explain what the application is I can figure it out.

 

[audioguru]

My electric model airplane weighs only 400 grams and uses a 67W motor.
Your motors are only 60W.

You can look up Underwater Personal Submarine to see how much more power they use.

When a motor is running in one direction then you suddenly slam it into reverse without leetting it slow down then there is severe strain on the motor.

 

[crutschow]

The contact current voltage is not clear to me. Some relays only give a current ratting for the contacts while other give a current and a voltage. Maybe and EE type could say more about that and if you need to add a cap to prolong the life of the contacts.

The contact voltage rating is basically for flashover concerns. That is, if the voltage is high enough an arc could form when the contacts switch which would maintain the current flow until the contacts burn away. This is generally not a concern for 12V circuits.

A small capacitor across the contacts will help protect the contacts but too large a value may actually weld the contacts from the surge current into the capacitor. Often a small resistor is added in series with the cap to limit this surge.

 

[holdit]

Are you saying that the relay 1 and 2 could be on when power is applied? You want to use relay 3 to prevent power from flowing through 1 and 2 at power on time.

I am afraid that I still do not understand. Maybe if you explain what the application is I can figure it out.

i have a pic 16f628a going to a uln2003a to control 3 relays (no problem)
as in picture attached

but as you can see the motors are moving as soon as power is appiled
so i needto control them with relay 3
these relays dont have a off postion c(pole1) nc no /
but use relay3 as 2 indivaiual spst

I think i better start a new thread as this is no mine iam sorry for butting in like that it was very rude of me sorry

 

[Pcolaboy]

Ok I think I found a relay and switch that will fit my needs:

**broken link removed**

**broken link removed**


The coil on the relay is operated at 5V while the contacts are rated for up to 8A @ 18VDC. I bought 6 of the relays and 3 of the switches.

Pcolaboy

 

[mneary]

I should chime in here that a deep-cycle marine battery may be overkill. 12V 7Ah sealed lead acid batteries aren't very expensive and might fit inside your ROV. Of course you'd have to shed a lot of ballast. I don't know how big your ROV is, but in the end a small SLA should weigh (and cost about $22) a lot less than 100 ft of 14AWG stranded wire.