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Discussion Starter · #1 ·
How much power do you lose, compared to an analog controller, from a PWM controller like my SCP1 with analog cart? PWM is the same method of applying power used in RC car speed controllers. I still dabble a bit in the Mini-Z world, where it's common to replace the FETs in the speed controller with some aftermarket parts with lower ON resistance. I've done it to my Mini-Z, and it makes a difference. Too much difference for me. I suck at RC, so I had to dial back the peak power on my radio after doing this mod. I know that it's very unlikely that my analog cart's ON resistance is as low as an analog controller's full throttle contacts. So has anyone done any testing to compare power and/or top speed of a PWM controller vs analog?

Or does the SCP analog cart have a full throttle relay? If it does, I can't hear it.
 

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Yes I have tested some brands of PWM and linear controllers to compare the resistance on full power. I haven't measured a SCP1.

Ideally a controller should have zero resistance on full power. Any resistance will reduce the power and top speed but the difference may be too small to be worth bothering about.

There is a difference between different brand of controller but the difference is all down to the detailed design and build of the controller, not whether it is PWM or linear.

That difference is big enough to concern those trying to get ultimate performance from high powered modern slot cars (tens of milliohms and 20+ amps means several percent less power) However, the difference is too small to be worth worrying about for home set cars (tens of milliohms and a fraction of an amp isn't likley to be noticeable.)

All the controllers I've measured with really low on resistance have the blast relay or power MOSFETs mounted near the plug. The resistance of the wire too and from the handle is more than the total on resistance of the really low on resistance brands.

There is no need for a blast relay if MOSFETs with really low on resistance is used, The MOSFETs for the high power stuff have very low on resistance, inevitably their current ratings are way above the current the motors take. If MOSFETs are specified with just enough current rating to drive the motors they will inevitably have more on resistance than desirable so there would be some advantage in adding a blast relay. I assume that's why after market MOSFETs are used in RC.
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Greg Gaub
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There is no internal relay in any of the SCP cartridges that I'm aware of, however the High Amp aka METAL cartridge does have a connection point to trigger a relay for full power, and slot.it provide instructions on where to put that connection and how to wire a relay. It should be on their site somewhere. The "regular" analog cartridges do not have that connection point, though.

I've found that the metal cart gives me plenty of power and braking without the need for the relay, though. I'm certainly not losing any races as a result of whatever minute power loss occurs through the MOSFETs.
 

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Rich Dumas
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Most electronic controllers bypass the transistor, etc. when you pull the trigger all the way, I don't know if that is the case with a Slot.it controller. I use a Difalco Genesis controller and that has a full speed blast relay located in a dongle along with the transistor and heat sink and a second blast relay for the brakes. The dongle is only a foot from the track connections in order to minimize the amount of wire in the circuit.

Someone with a Slot.it controller could do a test with a load on the circuit to see if the voltage to the track is the same as the voltage at the power supply.
 

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Discussion Starter · #5 · (Edited by Moderator)
Ideally a controller should have zero resistance on full power. Any resistance will reduce the power and top speed but the difference may be too small to be worth bothering about.
Well, yeah... that IS the basis of my question.

There is a difference between different brand of controller but the difference is all down to the detailed design and build of the controller, not whether it is PWM or linear.

That difference is big enough to concern those trying to get ultimate performance from high powered modern slot cars (tens of milliohms and 20+ amps means several percent less power) However, the difference is too small to be worth worrying about for home set cars (tens of milliohms and a fraction of an amp isn't likley to be noticeable.)

All the controllers I've measured with really low on resistance have the blast relay or power MOSFETs mounted near the plug. The resistance of the wire too and from the handle is more than the total on resistance of the really low on resistance brands.

There is no need for a blast relay if MOSFETs with really low on resistance is used, The MOSFETs for the high power stuff have very low on resistance, inevitably their current ratings are way above the current the motors take. If MOSFETs are specified with just enough current rating to drive the motors they will inevitably have more on resistance than desirable so there would be some advantage in adding a blast relay. I assume that's why after market MOSFETs are used in RC.
But are FETs with really low ON resistance used in Slot.it analog carts?

There is no internal relay in any of the SCP cartridges that I'm aware of, however the High Amp aka METAL cartridge does have a connection point to trigger a relay for full power, and slot.it provide instructions on where to put that connection and how to wire a relay. It should be on their site somewhere. The "regular" analog cartridges do not have that connection point, though.

I've found that the metal cart gives me plenty of power and braking without the need for the relay, though. I'm certainly not losing any races as a result of whatever minute power loss occurs through the MOSFETs.
I figured that there was no internal relay in the std analog cart. Wasn't sure about the high current cart. I doubt I've lost races due the minuscule power loss through the FETs, but... the local club track is something of a "horsepower track". In some classes, the trigger will be pinned for a majority of the lap. Not my favorite classes, but I race whatever the class is. In those classes, there's not much to differentiate 1st from 2nd from 3rd, etc. So losing a half a lap over an entire race could be significant. On a technical course, the ability of the driver to adjust the controller to his liking will likely be more significant than the slight power loss.

Most electronic controllers bypass the transistor, etc. when you pull the trigger all the way, I don't know if that is the case with a Slot.it controller. I use a Difalco Genesis controller and that has a full speed blast relay located in a dongle along with the transistor and heat sink and a second blast relay for the brakes. The dongle is only a foot from the track connections in order to minimize the amount of wire in the circuit.

Someone with a Slot.it controller could do a test with a load on the circuit to see if the voltage to the track is the same as the voltage at the power supply.
Agreed about most electronic controllers. But that doesn't apply to PWM controllers. And that's the basis of my question. PWM controllers WILL have a slight power loss at full throttle. How much? I don't know. That's why I asked the question. I have two other analog electronic controllers. Neither have relays, but both have full throttle contacts that bypass all electronics.

I have an SCP1 controller. I'm an engineer with access to equipment to characterize the controller. On the bench. But even if I determine that the full throttle ON resistance is 10 milliohms, or 100 milliohms, or 1000... what does that mean on the track? I know that it will depend on the track, too. Compared to a typical analog electronic controller, the myriad of controls on the SCP might do a better job of making a car easier to drive, which might more than compensate for the power loss. On other tracks, with other cars, that might not be the case. I was hoping someone had experience with this. The SCP controllers have been around for a while.

Thanks for the replies.
 

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(1) But are FETs with really low ON resistance used in Slot.it analog carts?

(2) Agreed about most electronic controllers. But that doesn't apply to PWM controllers. And that's the basis of my question. PWM controllers WILL have a slight power loss at full throttle.

(3) I have an SCP1 controller. I'm an engineer with access to equipment to characterize the controller. On the bench. But even if I determine that the full throttle ON resistance is 10 milliohms, or 100 milliohms, or 1000... what does that mean on the track? I know that it will depend on the track, too. Compared to a typical analog electronic controller, the myriad of controls on the SCP might do a better job of making a car easier to drive, which might more than compensate for the power loss. On other tracks, with other cars, that might not be the case. I was hoping someone had experience with this. The SCP controllers have been around for a while.
(1) The electronics are mounted in the SCP handle, The wiring resistance between the handle and plug will be more than the really low ON resistance other controllers achieve with MOSFETs or blast relays.
That's only likely to be worth bothering about if you are using motors that need the SlotIt high amp cartridge. If you are running high enough powered motors for that to be an issue, you could add a blast relay to the SlotIt high amp cartridge. MrF has told us about that in post #3.

(2) Some PWM controllers do have blast relays, some don't. The SlotIt high amp cartridge has the option to add one. All controllers (PWM and linear) will have a slight power loss at full throttle. Relays, MOSFETs and contact on the trigger all give a slight power loss at full throttle. I've measured a variety of controllers with both relays and MOSFETs. The lowest power loss ones which use relays lose about the same amount of power as the lowest power loss ones which use MOSFETs

(3) It's not difficult to measure the power loss using a resistor that takes the same amount of power as the highest power motors you want to run. Connect the resistor to the track rails, hook up the controller, put the trigger in the full power position and measure the voyage drop AT THE CONTROLLER HOOK UP. On the international standard raceway hook up that'll be the voltage drop between the black and white connection, but the track you use may have different connections. From that it's easy enough to calculate the percentage of the supply voltage being lost in the controller.

How much matters? When racing high powered cars, power reduction is sometimes an advantage. This is often called "choke", a rather confusing name which in this context means some form of power reduction, NOT inductance. Where resistance is used to reduce power, it's normally in the range from a few tens of milliohms up somewhat over 100 milliohms. That's how much resistance makes a noticeable difference with high powered slot cars.

Of course ohms law applies to resistances, so with the low current consumption of home set type cars blast relays etc. are likley to be pointless.
 

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Slot King
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(2) Some PWM controllers do have blast relays, some don't. The SlotIt high amp cartridge has the option to add one. All controllers (PWM and linear) will have a slight power loss at full throttle. Relays, MOSFETs and contact on the trigger all give a slight power loss at full throttle. I've measured a variety of controllers with both relays and MOSFETs. The lowest power loss ones which use relays lose about the same amount of power as the lowest power loss ones which use MOSFETs.
Any chance you could tell us which PWM controllers have a blast relay and which don't? It would also be great if you could post the actual result of your measurements.

It would really help the community if you did, I am sure plenty of people would find the information useful when making purchasing decisions

Bemoore, here is a link to the Slot It blast relay PDF

Let us known if you decide to do the modification.

Joel
 

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There are many important points to consider when making controller purchasing decisions. As discussed extensively on other threads things like is it suitable for your cars, is it the correct polarity for the track, does it suit your hand and driving stile, cost etc.etc.matter. Keeping to the issues already raised on this thread

Presenting all the detailed measurements with enough explanation to prevent misunderstandings is a lot of work, the conclusions are enough to help with making controller purchasing decisions.

When making purchasing decisions, an important conclusion of the testing is to forget about the insignificant differences in full power between anything with a blast relay close the plug and controllers such as Carsteen with high power MOSFETs close to the plug. Everything I've measured with no relay or electronics at the plug end has a higher on resistance. That higher resistance isn't enough to matter with the relatively low current motors that are pretty much universal in plastic chassis slot cars, but is more important for modern high current slot car motors that take over 10 times more than the "plastic chassis" type motors.

When making slot car controller purchasing decisions I think it's unwise to limit the choice to PWM. I'm well aware of the advantages of PWM over linear controllers in RC cars, and the reasons why PWM is pretty much universal with digital slot car chips. Those advantages are of no consequence in non digital slot cars, there are lots of excellent linear controllers on the market.
 

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The main shortcomings of cheap pwm controllers such as slot it scp ,ds pro4 ect is that they have no choke they only deliver the power differently but full power is what they deliver all the time,so if you have a car that's a bit of a handful, it will always be so ,as I have measured the slot it output at the rails and no matter the settings or knobs twiddling it does not lower the voltage at the rails ,same for the ds pro 4 ,even the basic truspeed pwm can be choked buy using the control on the circuit board,the upper end of the controller market properly turns the voltage up or down at the rails,and without that ability all the problems you may have with control will just be moved to a different place on the trigger throw the slot it controller could have been a brilliant tool but it's over engineered in the wrong places and under engineered in the right places shame,also why is so bleeding big
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Slot King
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300SLR, I don't think anyone would chose a controller purely on the theoretical losses they may or may not get at full speed. Because the OP is specifically about this topic, I thought it was appropriate to ask and the info would certainly be useful.

Shame, but no problem if your test results can't be posted.

Alan, as I recall, the SPC can be choked, somewhere among it's undecipherable controls there is a <child> mode that allows max voltage to be turned down.

There is another rather clever mode that allows power to be turned down all the way to 99% trigger travel, but yet retain full power at 100%.

As you might have guessed, I have never managed to detect a difference when setting mine up.

Call me a glutton for punishment, but in a final attempt at using a single controller to run everything from an NC1 to a strap motor, I have recently bought an SPC2 with a high current cartridge.

For the record, I have an SCD linear controller and it feel really rough compared to the delightful (but now defunct) DS4 pro.

If anyone out there has a DS4 pro for sale (even with broken switches), please get in touch.

Joel
 

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If there is a setting for choke I could not find it as no matter what you do it always sends full power to the rails.it just delivers it differently so you think it's choked. Which on a standard slot it car is probably ample but applied to 40k and above is no good I think what it does is only delivers a small amount of the full power but it's still full power ,but if there is a real.choke I'll be happy to be shown how it actually works
 

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Discussion Starter · #13 ·
Re: choke.... The SCP has a knob called Power Trim that works very much like a choke. It adjusts how fast power can be applied, very similar to chokes of old. The Power Trim adjustment controls the delivery of voltage. The chokes of old controlled the delivery of current. Similar effect, but not exactly the same. I have an analog controller with a choke knob, and I can't get to act anything like a real choke. The Power Trim knob on my SCP acts way more like a choke than anything else I've tried.
 

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Discussion Starter · #14 ·
If there is a setting for choke I could not find it as no matter what you do it always sends full power to the rails.it just delivers it differently so you think it's choked. Which on a standard slot it car is probably ample but applied to 40k and above is no good I think what it does is only delivers a small amount of the full power but it's still full power ,but if there is a real.choke I'll be happy to be shown how it actually works
What are you using to measure the voltage going to the rails? PWM controllers send power to the rails pulses of voltage. These pulses are full voltage, but the controller controls the duty cycle. I.e. how much time the voltage is on vs how much time it's off. The pulses are so fast that the power delivery is smooth. A cheap meter may show that the voltage at the rails is full voltage all the time.
 

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A proper automotive voltage meter,also when used to measure my carsteen it shows the voltage drop when you choke it up.which is why the only complaint I had with the ds 4 is you can't choke it up ,as in lower the. Voltage it only changes how it delivers the power it's either sharp or dull ,the slot it power trim does the same just changes how it delivers it not how much you get ,but the dislike may just be my driving style as others like em ,you never know,but it'd be boring if one size fitted all
 

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If there is a setting for choke I could not find it as no matter what you do it always sends full power to the rails.it just delivers it differently so you think it's choked. Which on a standard slot it car is probably ample but applied to 40k and above is no good I think what it does is only delivers a small amount of the full power but it's still full power ,but if there is a real.choke I'll be happy to be shown how it actually works
Sorry, but you missed it: there IS a way to limit voltage. Well, the equivalent to maximum voltage in PWM terms. This is clearly a case where the old adage applies: when all else fails, read the manual. Especially with something as complex and powerful as the SCP controller. And no: doing it is not simple but it is typically something you do once and that is it. I have done it with both my SCP 1 and SCP 2 controllers. And note that this mode is only available in "Linear" mode, not "Curve". And please note I only race in Analog: I do not know the first thing about digital!

The SCP 1 is slightly different but for the SCP 2:

  • Disconnect controller
  • Ensure the switch on top of the controller is in the MID position.
  • Press and hold the round brake button.
  • Plug in your controller
  • Click the top switch over to the "Slow" position while still holding the brake button
  • Release the brake button.

A successful change will be indicated by the fact that the LED below and between the Min Speed and Brake knobs that is normally green will now turn orange. Well, both he green and red LED's will be on simultaneously, if that qualifies as orange. The Curve/Max knob will now control the maximum voltage that the car receives while still maintaining the characteristics between 0 and full throttle that you set up (which BTW I do not bother with: I have it on linear because I like the car to do exactly what I do with the trigger).

The SCP 1 likewise describes how to get it into "Kid's mode"

Controllers are very personal things. I personally very much like the soft trigger action, the smooth trigger surface and the general "feel" of the controller. While it is not necessarily for everyone, it certainly works for me. Without having the bother of replacing resistance networks or having to clean resistance coils etc etc: a truly no maintenance controller that is absolutely consistent in performance and reliability. I find it a delight for long distance races as it does not tire you out and hurt your finger. FWIW: I was on the winning team of two North American 24 hour races in 2019 (Scaleracing BRM 1/24th and the Michigan 1/32 24 hour races). So the controller must be good for SOMETHING!
thumbsup2.gif


Of course when you read this you can find a thousand reasons why you think the controller is terrible: why does it not do this like this or why does it do that like that. I am not suggesting this controller is the right one for you. THE BOTTOM LINE IS: you have to be comfortable with the controller you use. If not, you will never be happy. To my mind, THAT is WAY more important than the technical details of the controller. Get one you like, get comfortable with it and practice with it. End of story, regardless of controller.

And again please note: I am not writing this to convince anybody of what a wonderful controller the Slot.it is. Your choice is your choice. I just wanted to correct a misconception for other people that might be considering the controller.
 

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Alan Wilkinson
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When MOSFETs first came into use for hobby based speed controls, they replaced the earlier designs which were transistors with a bypass relay.

I did get to chat with designers of the mosfet units and my main question was "why does this unit have multiple mosfets? Is it because a single mosfet can't handle the power? "

In short, the answer was "no".
The logic for multiple FETs is that multiple FETs in parallel reduce the voltage drop.
By using parallel mosfets , the voltage drop can be brought down to very low levels, removing the need for a "blast/turbo" relay.

Now I'm sure that the last 35 years has changed things but the same principle should hold true.
Does SCP2 metal have parallel fets? I don't even know.
Only Maurizio F would be able to confirm.

However, in the matter of "do I care"?
The answer is "yes" but I don't care as much as I care about Traction, Handling, Transmission and Reliability of the car because they come much higher in my priority list than power.
I will continue to use my pair of SCP2 units but maybe do some reading on the bypass relay option.

Alan W
 

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Discussion Starter · #19 ·
There are many important points to consider when making controller purchasing decisions. As discussed extensively on other threads things like is it suitable for your cars, is it the correct polarity for the track, does it suit your hand and driving stile, cost etc.etc.matter. Keeping to the issues already raised on this thread

Presenting all the detailed measurements with enough explanation to prevent misunderstandings is a lot of work, the conclusions are enough to help with making controller purchasing decisions.

When making purchasing decisions, an important conclusion of the testing is to forget about the insignificant differences in full power between anything with a blast relay close the plug and controllers such as Carsteen with high power MOSFETs close to the plug. Everything I've measured with no relay or electronics at the plug end has a higher on resistance. That higher resistance isn't enough to matter with the relatively low current motors that are pretty much universal in plastic chassis slot cars, but is more important for modern high current slot car motors that take over 10 times more than the "plastic chassis" type motors.

When making slot car controller purchasing decisions I think it's unwise to limit the choice to PWM. I'm well aware of the advantages of PWM over linear controllers in RC cars, and the reasons why PWM is pretty much universal with digital slot car chips. Those advantages are of no consequence in non digital slot cars, there are lots of excellent linear controllers on the market.
How fast does a motor have to be for the power loss to make a difference? My fastest motor is a 25K. I can't tell a difference in acceleration or top speed, but that doesn't mean that there isn't a difference. And maybe even if there IS a difference, the control of the SCP (which I really like) may more than make up for it.

I have a good analog controller. I got the SCP so I could try out digital with a trigger controller. I'm finding that I like using it for analog, too. I strongly suspect that the condition of the braids on my cars makes more of a difference than the slight power loss from the controllers MOSFETs, but I don't know that. That's why I asked.
 

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Discussion Starter · #20 ·
When MOSFETs first came into use for hobby based speed controls, they replaced the earlier designs which were transistors with a bypass relay.

I did get to chat with designers of the mosfet units and my main question was "why does this unit have multiple mosfets? Is it because a single mosfet can't handle the power? "

In short, the answer was "no".
The logic for multiple FETs is that multiple FETs in parallel reduce the voltage drop.
By using parallel mosfets , the voltage drop can be brought down to very low levels, removing the need for a "blast/turbo" relay.

Now I'm sure that the last 35 years has changed things but the same principle should hold true.
Does SCP2 metal have parallel fets? I don't even know.
Only Maurizio F would be able to confirm.

However, in the matter of "do I care"?
The answer is "yes" but I don't care as much as I care about Traction, Handling, Transmission and Reliability of the car because they come much higher in my priority list than power.
I will continue to use my pair of SCP2 units but maybe do some reading on the bypass relay option.

Alan W
Multiple FET's in parallel reduce the voltage drop, and also reduce the heat generated in the controller. Generated heat = power loss.
 
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