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Old 06-29-2011, 11:10 AM   #61
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Re-post...

To all those with the same setup, you WILL eventually have the same problem.

Theses starter boxes have little, flimsy contacts that, in stock form, handle ALL of the current the motors pull. Not quite the hot setup, IMO.

I had the same issue, so I made new contacts from copper(1/2" copper tube, smashed flat and cut/dremel'd to fit), but I still wasn't happy with the performance I was getting.

So I took it one step further and added a relay to handle the current.

This setup may be overkill, but it ALWAYS works and it's one less thing to worry about come race day.

And yes, it WILL start a Mack truck....

Gonna have to try this out.
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Old 06-30-2011, 08:55 AM   #62
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Anybody?? (caps have a arrow on the body for proper current flow)

Connect the capacitor to pin 85 or pin 86 on the relay, you want the arrow pointing to the pin. It doesn't matter which of the 2 pins you connect to because the polarity of the coil doesn't matter. Just connect the positive lead from the battery to the capacitor then the capacitor to the pin. This will require the capacitor to charge before the coil sees the voltage and switches the relay.

In all honesty, I think adding a capacitor is pointless for a couple of reasons. The main reason you're adding it is to create a brief delay before the relay switches and applies current to the motor. This will help reduce the current draw across the mechanical switch in the starter box.
So, when you add a relay, you are already getting a delay. It takes time for the coil to energize and switch to activate the motor.

It takes more time than most think too. If you don't believe me, connect your positive wire from your motor to the center pin (87a) on the relay. Activate your starter box and see what happens.
The wheel will start to spin before the coil in the relay is energized enough switch poles. It won't make a full rotation, but you will see it move then stop.

Reason 2 that I don't think a capacitor should be in is for the sake of your pit man. As someone previous mentioned, they have about a 1.5 second delay. Now try to imagine someone else operating your bump box and they keep hitting not thinking about there being a delay and it's not responding to them. Factor this into a race where people are rushing. You flame out for some reason, pit man rushes to get your car fired back up. He keeps bumping your box and nothing happens. You'll be on the drivers stand cursing that capacitor.

Reason 3: You're pushing down waiting for the capacitor to charge. Odds are you will be putting pressure to the point where the flywheel is making contact before the starter box starts spinning. Not a good combination. Not good for your starter box, battery, or high dollar engine especially if new and still has metal pinch. It will get stuck. Bad on battery and starter box because when you strain an electric motor is pulls more current. If you stop the motor, is the same as directly shorting out your battery.
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Old 06-30-2011, 10:12 AM   #63
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well said Pickle.
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Old 06-30-2011, 11:04 AM   #64
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OK, well in honesty, I had already hooked up the cap both ways, 85 to 86 and vise versa, no difference and no delay at all. as soon as the plunger switch made contact it would spin up,,no delay with the cap in place facing either direction. The motor would stay engauged for a second or so after I let off,,which I found odd. but I beleive it is the relay I am using.

The relay I am using is a Painless Wiring vehicle starter relay, which is a 20x20amp relay. It's designed to basically remove the vehicle starter soilenoid from the equasion in the event you have a slow cranking starter motor on your 1:1 vehicle. So I believe it might be just a bit to heavy duty for a rc starter box app and probably has a sneak circut to allow the relay to stay engauged and continue to spin after I let off.

I have another 40 amp relay and are going to give that a try this weekend. also try clipping the cap and see if that fixes the continuous cranking.
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Old 06-30-2011, 12:43 PM   #65
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OK, well in honesty, I had already hooked up the cap both ways, 85 to 86 and vise versa, no difference and no delay at all. as soon as the plunger switch made contact it would spin up,,no delay with the cap in place facing either direction. The motor would stay engauged for a second or so after I let off,,which I found odd. but I beleive it is the relay I am using.

The relay I am using is a Painless Wiring vehicle starter relay, which is a 20x20amp relay. It's designed to basically remove the vehicle starter soilenoid from the equasion in the event you have a slow cranking starter motor on your 1:1 vehicle. So I believe it might be just a bit to heavy duty for a rc starter box app and probably has a sneak circut to allow the relay to stay engauged and continue to spin after I let off.

I have another 40 amp relay and are going to give that a try this weekend. also try clipping the cap and see if that fixes the continuous cranking.
There can be a few things going on there. If you don't have your relay wired correctly, that will bypass the capacitor and eliminate the delay. Capacitor size has a lot to do with it also.

Let me explain capacitors a little
A capacitor discharges 7 times faster than it charges. When it reaches max capacity, current will skip right through it because current ALWAYS takes the path of least resistance.
So what that means is the first time you use your starter box, there will be a delay to charge the capacitor. When you release the starter box and the connection breaks, there's nothing there to continue drawing from the capacitor so it's left at a fully charged state. Capacitors can and will store voltage for years.
Now the next time you go to use your box, the cap is at peak voltage already so there's no charge time or delay and you think it doesn't work anymore.

Now in your case, when you let off the starter box, it keeps running for a little bit. That tells me that it's running off of the voltage stored in the capacitor and indicating that you don't have it wired up correctly.
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Old 06-30-2011, 12:44 PM   #66
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well said Pickle.

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Old 07-01-2011, 07:46 AM   #67
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It's wired up correctly, I suspect the cap is flowing the wrong direction and keeping the relay energized for a few brief seconds.
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