Hot grips, install a relay, winter's coming!

[Rob Frankham]

2 questions:
1 -Would this resistor drop the voltage from 14V to around 9 or 10 volts, which is what I need, and would it negatively affect increase actual power consumption.
2 - Would it need to be mounted on a heat sink plate or would it cool adequately if it was just hanging in the air on its own.
I'm open to alternate solutions.

Thanks again Rob.

1) Can't really answer that without knowing the characteristics of the heating elements. I would think there's a good chance it would be in the ballpark though. The easiest way to find out is to try it and measure the relevant voltages.

1a) The current would be reduced by putting the resistor in series with the two elements (which are themselves in parallel of course).

2) we can come up with an answer to that if we assume a drop of 4 volts across the resistor...

From Ohms law Amps(i)=volts (v) divided by resistance (r) thus 4 volts/2 Ohms = 2 amps.

From the power equation, Watts(w)=Volts (v) x Amps (i) thus 4 volts x 2 amps = 8 Watts.

The resistor is rated at 50 Watts so it will survive quite well. Looking at the spec for a similar resistor, I find that the 50 Watt rating requires the resistor to be bolted to a heat sink but the unmounted rating is 20 Watts (still well within spec).

That being said I would always mount such a component as a) it is relatively heavy and I would want to prevent fatigue fractures of the wires that might occur if it were suspended and b) even though it's within spec, it will get quite warm so it might damage plastic components if it rests against them.

Finallym I would expect the motor speed control unit you mentioned to work quite well but (a) you'd probably have to turn the variable reg up quite high to get any effect and (b) read the reviews before you buy... they aren't universaly complementary.

Rob

[gspd]

Thanks for the advice Rob.
I'm going install that resistor for the lower heat setting and I'll report back with the results.
Just wanted to make sure it was in the ballpark.

[Airbear]

Thanks to Rob for providing the theory in an easily digestible form, though I'll probably forget it all before the end of year exam.

[hal]

Is this the same grips as on my '97 R850R? That has a low - on - high switch, but don't know how it it set up..

[gspd]

Just got back from a 250 km test ride.
Outside temp 10 C (50 F)
The bike just loves this weather. Me? not so much.
120km/h cruising (75 mph)
Absolutely LOVE that higher 5th gear.

Grips on high, direct 14V from battery = TOASTY ROASTY HOT, borderline too hot actually.
Grips on low = via 2ohm 50W resistor = comfortably warm.
The resistor didn't get too hot, barely warm to the touch.

I also got to break in another new rear Metzeler Tourance.
3rd one this summer, the first two lasted about 12,000km each.

Thank you everyone for all the advice and pointers, especially Rob F, greatly appreciated!
luv ya'Airbear

[gspd]

Is this the same grips as on my '97 R850R? That has a low - on - high switch, but don't know how it it set up..

sorry, not familiar with that set up.

[gspd]

Now that I've established that the relay and dual intensity heated grip temperature switch works perfectly, I'm going to use the neutral switch circuit to ground the relay. I might need a second relay for this function. I might be able just to do the 87/87a thing, still working on that, but it might not work because I want that circuit off when the ignition is off. I'll use the same circuit to power the heated grips AND the accessory plug for my heated vest. This way they'll both get direct battery power via the relay, but only when the bike is in gear.
I want the heat to turn off when idling at a traffic light in neutral to minimize low rpm load on the alternator.
Neutral light on = heat off. Should work grrreat.
I pity whoever ends up with the remnants of my bike when the day comes that my cold dead hands are pried off its handlebars. Nobody will ever figure out all the wiring mods. Too bad, so sad.

[gspd]

Re. my previous post...The goal of this exercise is:
1 - Direct battery power via relay to hot grips and auxiliary socket (done)
2 - LOAD turns ON with ignition ON, and OFF with ignition OFF so grips can't accidentally left on when bike is parked (done)
3 - (the clincher) LOAD has to turn OFF when ignition is ON ONLY WHEN neutral light is ON. I think I can accomplish this relatively easily with 2 cheap relays.
My question for Rob: Can this be done with only one relay? If so, can you please elaborate?
I would like to use generic (cheap $3.00) 30-85-86-87-87a relays that I can get locally, not a special (expensive) relay that I would have to order.

This is how I would do it with 2 relays:

[Rob Frankham]

Nope, can't think of any way to achieve what you want to do using a single relay on it's own. I could do it using a simple semiconductor circuit to reverse the sense of the neutral switch (which is effectively what you are doing with the second relay) but that doesn't fulfill the specified conditions.

Rob

[gspd]

Nope, can't think of any way to achieve what you want to do using a single relay on it's own. I could do it using a simple semiconductor circuit to reverse the sense of the neutral switch (which is effectively what you are doing with the second relay) but that doesn't fulfill the specified conditions.

Ya, thanks Rob, that's what I thought, but I wanted your opinion just to be sure.

Sooo.... I taped 2 relays together and wired everything up and it works perfectly.
I'll pretend it's just one big $6.00 relay.

Another happy ending.