controller, relay or...

jdcburg · #1 (**permalink**) 07-27-2009, 06:18 PM

OK, I'm already on to the next question. I want to power my ebuild with a 24 volt 350 watt motor. I am willing to pedal start and then have the motor kick in to help on the hills. Deacon has written eloquently about the pulse jet method of operating and I think that would work for me. So should I get a controller, a 24 volt relay or just a big heavy duty 30 amp switch? I'm leaning towards the controller as I think it might help keep me from burning up the motor. Razor has one matched to the motor I am interested in for $19 + $6 s/h, but I'm no electrical engineer and there's a lot of wires coming out of those things! There are generic controllers as well for a little more on eBay. Are they simpler to hook up? Would anybody here be willing to walk me through the process with either the Razor one or a generic? thanks - jd

deacon · #2 (**permalink**) 07-27-2009, 08:29 PM

I use the controllers these days thought I honestly don't see any big advantage. I wouldn't recommend one over the other to be honest. With a controller you need a throttle so the pulse method really isn't much of an option.

The truth is you are going to run it wide open throttle most of the time with a controller. But if you do get one you can leave most of the wires unhooked. You need to hook up the battery wires, the motor wires, the throttle wires, and if the controller has a switch set you need to jumper them together or use them for a kill switch. My kill switch is a household switch inline on the battery side.

If you do not use a controller you need a heavy duty fuse and switch for sure. Your biggest stress on the engine is starting from a dead stop and hills so high they slow you to a crawl. The controller keeps your wiring from burning up in those situations I think.

Hysteresis · #3 (**permalink**) 07-28-2009, 10:33 PM

Controllers are mainly used for speed control. Depending on the size of your motor and your application they may not be what you are looking for. If you are just going to full load amps with the throttle instantly then a switch may be what you are looking for. It's slightly more dangerous to do that though as you may get all that torque at an unexpected time if you aren't careful.

When you are sizing fuses for your application a quick way to do it is to multiply the full load current rating of the motor by 1.25 this will allow for the inrush current to establish the field and still protect your equipment during normal operation. You don't want to put a massive fuse on a motor that is only drawing a few amps, might as well just hard wire it because that is defeating the whole purpose of the fuse.

jdcburg · #4 (**permalink**) 07-29-2009, 06:27 PM

Gents - thank you for your responses. I just ordered a 40 amp relay. I will probably use a deadman switch to power up the motor. That way if things get too exciting I can just release the switch and that should shut everything down. So if my math is correct, a 24 volt 350 watt motor will draw 14.6 amps. 14.6 times 1.25 = 18.25, so a 20 amp fuse or circuit breaker is about right? As I said, I plan to pedal start and use the motor to help on hills. I have ordered a geared down motor designed for a Razor Dirt Quad ($36 + s/h) and hope to get it put together fairly quickly, so I'll let you know how things progress - jd

deacon · #5 (**permalink**) 07-29-2009, 07:28 PM

good luck and how are you attaching it

jdcburg · #6 (**permalink**) 07-29-2009, 09:57 PM

Thanks Deacon. I'm not sure what you are asking me about attaching, so I'll give you the whole enchilada: I acquired a matched pair of old Huffy 3-speed bikes. The kind with the internal gears in the rear axle. What we called an English bike when I was growing up. I put the rear wheel from one on the front of the other with the sprocket on the right, so it will engage to drive forward and freewheel when the motor is shut off. I've already done that and it fits fine. I'll mount the motor on a rack above the front wheel with the sprocket on the right. I'm shooting for a final drive ratio of 12-14:1 and speeds in the mid-teens. I think I read in the archives that you did something like that. Did it work for you?
Because I'll be using a relay, I can use a lighter duty switch. Probably Radio Shack has a deadman rocker or toggle switch. Interestingly, I emailed Razor about the motor, asking questions about final rpms, sprocket size, etc, explaining that I wanted to use the motor to power an ebike. They wrote back saying: "We are not able to assist with making modifications to or building a product. Our goal is to make sure that your product is as safe as possible." Big help, hey? I'd like to mount the batteries (2-12v 12ah sla's) between my legs above the crank or along the front tube but I'm waiting to see them before I make the final decision on that.
So that's the plan. See any major flaws or have any suggestions? jd

deacon · #7 (**permalink**) 08-03-2009, 05:30 PM

I wanted to let you know i went back to a simple on off switch on a 350 watt motor with a friction drive and it works perfectly. I did that after the controller died for some reason.

jdcburg · #8 (**permalink**) 08-03-2009, 09:22 PM

Thanks Deacon. The relay came and I think I've figured out how to hook it up. I'll be working off the place the next few days so I won't have a chance to work on it but maybe over the weekend...

deacon · #9 (**permalink**) 08-03-2009, 10:37 PM

let me know how it goes I'm always curious about other builds. My progect not is to build a friction drive mechanism from scratch. Right now I'm using scooter wheels assemblies.

jdcburg · #10 (**permalink**) 08-12-2009, 09:19 PM

It works! I finished it and took out a couple of times for test runs this evening. I ended up using a 40 amp Bosch type relay from ElectricScooterParts.com (~$8 w/s&h) and a momentary toggle switch from Radio Shack ($3). The Razor motor had a #25 sprocket on it. The shaft is 11mm (7/16") with a 2x4mm key so I bought a 9 tooth bike sprocket that fits the shaft from EScooterParts ($23). It was a little narrower so I had to file notches in a couple of 7/16 washers to shim it out. I built a rack out over the front wheel out of a 2x4, 2 pieces of 1x1 angle aluminum and some shelf brackets. The 2 12v 12ah SLAs are secured to a shelf between my legs just above the crank.

I'm happy with the way it performs. I had the 3-speed front axle set to low gear and it climbed "heart attack hill" near my house pretty well with me pedaling like I was on level ground. When I stopped pedaling, it slowed down to where I thought it might cause problems, but picked up nicely when I started pedaling again. Later I set the front axle to high gear and it went along on level ground about as fast as I could pedal comfortably in high gear - I'm guessing about 18-20 mph. I doubt if it will have enough "hill power" in high gear but I may get a shifter for the front axle sometime. For now I just tie it tight for low gear and let it loose for high gear.

I took some pictures during construction and I'll take some more tomorrow if the weather cooperates. I'll take it for another (longer) test run too. Probably another post or 2 and I'll be able to post the pictures here.

Thanks again to all of you for the helpful suggestions and encouragement - jd