Can I use 5-pin relay to reverse DC motor direction? - Page 1
Forum section: electronics / projects

author: adauphin
author_rank: Unknown
timestamp: May 11, 2016, 04:40:22 pm
content: My kids Power wheels is 24V, uses two motors and I'm going to install a scooter ESC but the ESC doesn't have reverse. Could I use a standard 5-pin relay and use the forward, reverse lever to actuate the relays? There's a two-pin switch on the forward/reverse lever so I'm thinking that I could use the closed position on the relay to provide the forward direction and the open for reverse..is this possible?So basically the output of the ESC to the relay or relays, then to the motors instead of the ESC to the motors.Would a 12V signal to the direction switch then a wire from the other terminal of the direction switch to the relay allow this to happen?Hope that makes sense.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: May 11, 2016, 04:48:02 pm
content: By "standard 5-pin relay" do you mean a Single Pole Double Throw (SPDT) relay? Two pins for the coil, one pin for the movable contact, one normally open, one normally closed contacts = 5 pins?I think to do the polarity reversal you are asking about you will need a Double-Pole Double Throw (DPDT) relay, so it will have 8 pins instead of 5.

author: ovnr
author_rank: Frequent Contributor
timestamp: May 11, 2016, 04:49:40 pm
content: No, you need a DPDT relay, which will have 8 pins in total. You may also use two SPDT (5-pin) relays.

author: adauphin
author_rank: Unknown
timestamp: May 11, 2016, 08:29:38 pm
content: Quote from: alsetalokin4017 on May 11, 2016, 04:48:02 pmYes, I believe that's what I was thinking of.Quote from: ovnr on May 11, 2016, 04:49:40 pmUsing two SPDT 5-pin relays, would this be one for each motor or combined and wired together with a double lead somewhere in the wiring across the relays?

author: ovnr
author_rank: Frequent Contributor
timestamp: May 11, 2016, 08:44:57 pm
content: Quote from: adauphin on May 11, 2016, 08:29:38 pmTwo relays before both motors, unless you want it to spin wildly out of control. Just connect the motors in parallel - taking into account that one of them might need to be reversed, not sure how the mechanics are set up - and attach them to the relay(s).Here's how you'd connect it if you use two SPDT relays:Remember to lay off the throttle when switching drive direction.

author: adauphin
author_rank: Unknown
timestamp: May 11, 2016, 09:05:45 pm
content: Quote from: ovnr on May 11, 2016, 08:44:57 pmOk, I see how it's working now....I did find a good DPDT pic and see how that would work as well. The motors are in parallel so that's correct. Forgot to mention, the reason I would like the 5-pin relays is I need them to withstand 50-60A for at least 30 seconds to 1 min at times and the 8-pin relays I have seen aren't as robust. I have found some 80A 5-pins but not sure how robust they are.

author: adauphin
author_rank: Unknown
timestamp: May 11, 2016, 09:16:41 pm
content: So I can see where two 5-pin relays could possibly pose a risk if one relay doesn't switch, as opposed to a DPDT relay which would be less likely to have an issue.So what relay's do you recommend for an 80A rating and is there an 80A DPDT relay avail? I'm going with 80A for some wiggle room, but I think a 60A would work fine.I was thinking of a polarity switching solenoid but it seems most are intermittent duty not continuous.This is what I've found if I wanted to make it as robust as I could...albeit expensive. A cheaper alternative would be great...http://www.gamainc.com/200aprc/

author: ovnr
author_rank: Frequent Contributor
timestamp: May 12, 2016, 12:03:02 am
content: Actually, when you mention it: Swap the motor and ESC connections in my diagram, so the ESC is connected to the NC and NO pins, and the motor to the common pin (like in alsetalokin4017's diagram). This way, if one relay fails to switch, the motor will simply brake (hard...); the ESC will be unharmed.DPDT relays will probably not be much more reliable; your biggest worry is the contacts welding, and that can lock up one side of a DPDT relay without affecting the other. The only advantage (reliability-wise) is that you only have one set of coil wirings to worry about.As for sourcing cheap relays: If you want high ratings, your options are quite limited. I'd honestly suggest dumping the money into a better ESC; I hear theRageBridge 2is pretty good - and you won't blow it up. Plus you can drive it like a tank with different inputs per side.

author: adauphin
author_rank: Unknown
timestamp: May 12, 2016, 01:06:25 am
content: The Ragebridge looks nice, I don't mind spending a little more for quality.I will swap the leads when I get it hooked up. I have two vehicles to modify so the first one I will run dual 1000W controllers with 100 amp Bosch 5-pin relays.I'll give it awhile and see how it goes, for the 2nd vehicle I will likely use that Ragebridge.Thanks for the tip on that controller.

author: adauphin
author_rank: Unknown
timestamp: May 12, 2016, 10:47:30 pm
content: With regards to this setup, could I also add an inrush current limiter while maintaining peak current flow once up to speed?I guess a soft start is what I'm after and I'm not well versed with these current limiters.I guess a 5 to 10 amp initial current would be fine but I would want it to build back up rather quickly. Trying to reduce the chance of gearbox damage from a high shock start or from changing direction accidently while moving.

author: ovnr
author_rank: Frequent Contributor
timestamp: May 13, 2016, 09:23:43 am
content: Quote from: adauphin on May 12, 2016, 10:47:30 pmThat'd generally be an ESC thing, not related to the relays. The Ragebridge ESC I linked will perform current limiting to whatever you set it to; mind you, you will probably want to stick a microcontroller between it and the rest, and you can just do ramping there too if you want an even more gentle start. I'd also remind you that currently, it will apply the full stall torque to the gearbox whenever started, assuming there isn't a clever ESC in there already.If you're doing pure relay switching of the entire mess, no, it's not very practical. Yes, you can buy an off-the-shelf limiter if you can find one; it just seems like a bit of a waste.

author: adauphin
author_rank: Unknown
timestamp: May 13, 2016, 12:22:57 pm
content: The stock setup is only an on/off foot switch, with low being the 1st step and that runs the motors in parallel, then high is in series.I suppose the ESC will have somewhat of a softer start, but the current limiting feature on those scooter controller is only an overload safeguard AFAIK. They do have a potienometer to control overall speed of the motors bit not related to an inrush of current.I will look into that Ragebridge controller for the 2nd vehicle for sure.I will try the scooter controller and see how it works in regards to startup...won't be until another week though.