PWM Controller for Motorcycle Heated Grips

[60Hurts]

All,

I have Oxford heated grips on my motorcycle and it only has a single controller for both grips. The problem is that the right (throttle grip) is insulated from the handle bar due to the throttle tube whereas the left grip is on the handle bar directly. So no matter the setting the right grip is too hot and the left grip is too cold. I am following other riders who have used a pulse-width modulator speed controller to make an independent temp controller for each grip.  I have found a PWM speed controller that is rated for 5A (grips are ~3A max 12vdc but I rarely need full blast), Amazon link;

https://www.amazon.com/RioRand-Motor-Controller-Control-Dimmer%EF%BC%882PCS%EF%BC%89/dp/B07WGT8K82/

I think this will work (open to critiques of this choice). In any case, the controller says it can use 3V 6V 12V 24V or 35V input voltage but obviously on a motorcycle it will be 12v.  Below is an image of the PCB with a contact to jump for 3-15v and unjumped for 5-35v input so my question is what is the electronic purpose and advantage for jumping those contacts in my case since the range overlaps. Thanks!

[Someone]

90% chance its some form of regulator (possibly just resistive dropper) that would add unnecessary dropout/heat below 15V, but without it some parts would be outside the maximum ratings above 15V supply.

For automotive, always consider transients above the nominal operating voltage 12V has lots of not 12V conditions. In general if it isn't specifically described for automotive use, don't connect an electronic devices power directly to a vehicle.

[60Hurts]

For automotive, always consider transients above the nominal operating voltage 12V has lots of not 12V conditions. In general if it isn't specifically described for automotive use, don't connect an electronic devices power directly to a vehicle.

Charging system is a Flintstone era permanent magnet generator with a shunt regulator/rectifier.  Volts at the battery when riding is <14vdc but variable with RPM and around 12.8v at idle so it should be okay?  This an old bike but it does have an electronic control unit (ECU) that interfaces with a number of sensors (air and coolant temp, intake pressure, throttle position, etc.) and controls the fuel injection.  Do you think the PWM would create electrical noise on the main bus that could impact the ECU? If so should I add a low-pass filter or ferrite bead inductor on the supply power to the PWM controller to block any electrical noise upstream?

[60Hurts]

I haven't really done anything on this project since November (see above) but in mulling this over I was thinking that perhaps it is possible to lower the power in the right grip by placing a resistor in series with the right heated grip. Even better would be to install a potentiometer or rheostat (not sure what the difference is here) so I could adjust the resistance to lower the power in the right grip till comfortable.

I measured the resistance and the left grip (too cold) is 6.3 ohms and the right grip is 7.3 ohms (too hot). Assuming a nominal voltage of 13vdc and V=I*R yields a current of 1.781A on the right grip.  Using P=I^2*R to get the right grip power at 23.15W. If I put a 1 ohm resistor in series total resistance is now 8.3 ohms and current reduces to 1.566A and right grip power of 17.91W for a reduction of power (and I assume heat) of ~30%. My guess is that I don't need to reduce the heat that much but with a potentiometer or rheostat it would be adjustable. At max resistance the power of the resistor added would 2.5W.

Here is where I need some advice (apart from checking my math or a better circuit design or any other caveats). How do I find a 1 ohm, 2.5W potentiometer or rheostat? Pot/RS specs don't give a range but I assume that a 1 ohm pot is adjustable from ~0 to rated ohms, is that correct? Pots seem to be tiny ohms and low power whereas rheostats seem to be high ohms and high power so I am not sure which way to go. What about range or sensitivity of the control?  In other words, how do I make sure that tiny movement of the pot/RS doesn't cause big changes in power making it impractical to adjust? Also, is 2.5W a lot of power/heat to dissipate?  Would it need airflow or could I safely put it in an enclosure? Metal or plastic ok?

Thanks.

[brucehoult]

I haven't really done anything on this project since November (see above) but in mulling this over I was thinking that perhaps it is possible to lower the power in the right grip by placing a resistor in series with the right heated grip. Even better would be to install a potentiometer or rheostat (not sure what the difference is here) so I could adjust the resistance to lower the power in the right grip till comfortable.

Dumb question maybe, but why not just add a similar insulating tube to the left grip?

My 1995 R1100RT (owned from new) has factory heated grips and I've never noticed any particular difference between the two sides. The control is pretty crude though, just a three position lo / off / hi rocker, so it's never the right temperature, but it takes a long time to go from "too hot" to "too cold" or the reverse.

[60Hurts]

Dumb question maybe, but why not just add a similar insulating tube to the left grip?

My 1995 R1100RT (owned from new) has factory heated grips and I've never noticed any particular difference between the two sides. The control is pretty crude though, just a three position lo / off / hi rocker, so it's never the right temperature, but it takes a long time to go from "too hot" to "too cold" or the reverse.

Not a dumb question but there is no room for any tube or insulation on the left grip.  I was thinking about wrapping the handle bar with teflon tape (high insulator) but the left grip is a really snug fit to the bar and secured with glue so no room. I'd guess that with OEM grips (mine are aftermarket Oxfords) they adjust the number of resistance coils left versus right to balance the heat to compensate for the throttle tube.  The controller on the Oxford is nice as it has 5 settings from 35-100% power.

[themadhippy]

but I assume that a 1 ohm pot is adjustable from ~0 to rated ohms, is that correct?

yep

Pots seem to be tiny ohms and low power whereas rheostats seem to be high ohms and high power

nope both come in a large range of resistance and power ratings,the difference is a pot has 3 connection ,both ends of the track and a wiper,a rheostat only has 2 connections

[Xena E]

Beware! Potentiometers are rated across their tracks, generally not for power taken from their wipers.

Personally, I'd go for PWM, though the one you have pictured looks sketchy, (that D pak device doesn't look as if it's leads are on the pads properly).

XE

[60Hurts]

So after thinking about this further I am going to just wire an inline fuse holder in series with the right grip power so I can easily add resistance to the circuit. The fuse holder will make it easy to swap resistance to get the power where I want it with a little experimenting.

The nominal power in that grip now is 23.15W and using my uncalibrated hand to measure I'm guessing that the power needs to drop 10% to be comfortable. So the target power is 23.15x0.9 or 20.8350W and with P=I^2*R with R of the grip at 7.3 ohms that yields a current of 1.6894A. Using V=I*Rt with nominal voltage of 13vdc and Rtotal=R1+7.3 yields R1=0.395 ohms to add in series to knock the power down about 10%. Rounding to 0.40 I get a power drop of 9% instead of 10% which is close enough. All these calcs were based on a nominal voltage of 13vdc so I calculated the power on the 0.40 Ohm resistor at 14vdc and got 1.3223W. So I need a 1.5 or 2W, 0.40 Ohm resistor. I briefly looked online but it doesn't look very common but I will keep looking.

My Plan-B is to wire five 2 Ohm resistors in parallel which works out to be 0.40 Ohms. Assuming that the current is evenly spit between each resistor at 14vdc the power is about 0.2646W. So I would need five 2 Ohm, 1/2 W resistors which seems pretty common.

[Ian.M]

0.39 ohms is a standard E12 series resistor value. When dissipating their rated power, the surface temperature of some types of power resistors can reach  200 °C , so to keep the temperature under 90 °C (to avoid melting wire insulation), assuming 0 °C ambient, you need at least a 3W resistor.  Note that metal cased power resistors with a flat mounting surface and mounting holes *MUST* be properly heatsinked to reach their power rating.   Without a heatsink they may not be capable of even 20% of their rating.

[60Hurts]

0.39 ohms is a standard E12 series resistor value.

This is really helpful as I don't have a background in electronics and I am now learning about the E-series of resistors. I was also looking at E3 (40% tol) and E6 (20% tol) which both have a standard of 0.47 ohms and E12 (10% tol) which has the 0.39 resistor you mentioned.  What is interesting, in my case, is that these tolerances actually give me a way to adjust the power drop in the right grip by just swapping a resistor. For instance for an E3 at 0.47 ohms the nominal power drop would be -11.7% but due to the tolerance range it could be as low as -7.3% and as high as -15.9% for E3 resistors. E6 at 0.47 ohms nominal power drop is also -11.7% but the range due to tolerance would be -9.6% to -13.8%. E12 at 0.39 has a nominal power drop of -9.2% and a range of -8.9% to -10.8%.  So for my purposes the higher tolerance resistors might be useful as a means of adjusting the power.  If these E3 resistors are cheap enough I could buy a bag of them and have a range of resistors (and thus power drops) to try.

When dissipating their rated power, the surface temperature of some types of power resistors can reach  200 °C , so to keep the temperature under 90 °C (to avoid melting wire insulation), assuming 0 °C ambient, you need at least a 3W resistor.  Note that metal cased power resistors with a flat mounting surface and mounting holes *MUST* be properly heatsinked to reach their power rating.   Without a heatsink they may not be capable of even 20% of their rating.

I will definitely have to think about the heat because I don't want to melt things.  Also, in my prior post I calculated about 1.5W max at 14vdc and just rounded the power up to 2W thinking that would be enough margin. But you make a good point that I hadn't thought of which is that rated power dissipation is dependent on max cooling so maybe I should double expected max for extra margin.

[Ian.M]

You need to know about derating.  The nominal power rating is at what ever the device's max. temperature rating is, and assumes 25 °C ambient.   For a 200 °C rated resistor that's a 175 °C temperature rise difference.  If the ambient is higher and/or the max temperature *you* can tolerate is lower, the power it can handle will be:
Psafe = Pnominal * safe_temp_rise / (Tmax - 25)

This can be very restrictive if the ambient temperature is high, and the part must remain cool enough to briefly touch without injury.   

In your application it wouldn't be unreasonable to use a 5W or even 10W resistor to be confident it will remain cool enough to be safe in close proximity to a wiring loom or plastic parts.

Also, real world tolerances don't work that way - they are just a guarantee that the odds of getting a value outside the tolerance range is negligible and say nothing about the distribution within the tolerance range. e.g. a single manufacturing batch is likely to have a mean resistance biased towards one end or the other of the tolerance range, as it isn't worth stopping the line to adjust till QA determines they are starting to go out of spec, and if the manufacturer sells a closer tolerance version of the part, the wider tolerance parts may be the rejects from the closer tolerance production, so have a total gap in the middle of their distribution, or if there is more demand for the wider tolerance part, actually be the closer tolerance one marked as wider so as not to spoil the market for the close tolerance part!  Therefore don't expect to be able to select on test to get a specific resistance value within the tolerance range unless you are lucky.

[AndyC_772]

Just FYI, the Oxford 'evo' grips have the version 9 controller, which has closed loop regulation of the temperature of each grip individually. So do the 'PRO' grips which have the controller built in.

[Zero999]

The problem with adding a resistor is power dissipation.

I would recommend PWM. The controller mentioned in the original post looks reasonable. Leave it unbridged for 5V to 35V operation.

It's true there can be voltage spikes, but the battery should take care of them. Yes, if the battery is disconnected, when the engine is running, then there can be high voltages, but as long as that doesn't happen, then it'll be fine. That controller is cheap enough, that even if it does blow up, it's no big deal. Once you've got one and confirm it works, buy a couple spare. It already has a fuse, but you might want to add another fuse, closer to the battery.

[themadhippy]

The problem with adding a resistor is power dissipation.

use 2 resistors and mount em in the foot pegs as foot warmers

[60Hurts]

You need to know about derating.  The nominal power rating is at what ever the device's max. temperature rating is, and assumes 25 °C ambient.   For a 200 °C rated resistor that's a 175 °C temperature rise difference.  If the ambient is higher and/or the max temperature *you* can tolerate is lower, the power it can handle will be:
Psafe = Pnominal * safe_temp_rise / (Tmax - 25). This can be very restrictive if the ambient temperature is high, and the part must remain cool enough to briefly touch without injury. In your application it wouldn't be unreasonable to use a 5W or even 10W resistor to be confident it will remain cool enough to be safe in close proximity to a wiring loom or plastic parts.

I will definitely take this into consideration, thanks for the info.  That said, the coldest I would ride would be 55 °F (12.8 °C) and I probably would not need grip heat over ~65 °F (18.3 °C) so that is the ambient temp range. Also, the resistor will be near the handle bars that get a lot of airflow since I am mostly moving when using the grips. Anyway, lots to think about.

Also, real world tolerances don't work that way - they are just a guarantee that the odds of getting a value outside the tolerance range is negligible and say nothing about the distribution within the tolerance range. e.g. a single manufacturing batch is likely to have a mean resistance biased towards one end or the other of the tolerance range, as it isn't worth stopping the line to adjust till QA determines they are starting to go out of spec, and if the manufacturer sells a closer tolerance version of the part, the wider tolerance parts may be the rejects from the closer tolerance production, so have a total gap in the middle of their distribution, or if there is more demand for the wider tolerance part, actually be the closer tolerance one marked as wider so as not to spoil the market for the close tolerance part!  Therefore don't expect to be able to select on test to get a specific resistance value within the tolerance range unless you are lucky.

Great explanation. I will add my idea to my list of brilliant ideas dashed upon the rocks of the real world.

[60Hurts]

Just FYI, the Oxford 'evo' grips have the version 9 controller, which has closed loop regulation of the temperature of each grip individually. So do the 'PRO' grips which have the controller built in.

That is good to know. Mine is an older model and the whole project started when one of the connectors broke (the early Oxfords had crappy connectors) so I pulled them to replace all the connector. Once I had them out  I started thinking about how to solve the heat differences. It was supposed to be fun Winter project, lol.

[60Hurts]

The problem with adding a resistor is power dissipation. I would recommend PWM. The controller mentioned in the original post looks reasonable.

I tend to agree but this was supposed to be a Winter project and it is already Spring and getting warm enough to ride.  If I add the inline fuse holder on the right grip and resistor gets too hot I can alway plug in a high amp fuse and I am back to where I started except the connectors are fix (see reply above).

Leave it unbridged for 5V to 35V operation.

Can you explain why? Just curious.

It's true there can be voltage spikes, but the battery should take care of them. Yes, if the battery is disconnected, when the engine is running, then there can be high voltages, but as long as that doesn't happen, then it'll be fine. That controller is cheap enough, that even if it does blow up, it's no big deal. Once you've got one and confirm it works, buy a couple spare. It already has a fuse, but you might want to add another fuse, closer to the battery.

I won't have time to do a PWM controller till next winter but thanks for the info/tips.

[bson]

I haven't really done anything on this project since November (see above) but in mulling this over I was thinking that perhaps it is possible to lower the power in the right grip by placing a resistor in series with the right heated grip. Even better would be to install a potentiometer or rheostat (not sure what the difference is here) so I could adjust the resistance to lower the power in the right grip till comfortable.

This is how all heated grips I've owned have worked, but my experience is limited to BMW and H-D.  In addition, the two grips have been in series behind a single rheostat.