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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.
No point in bothering with blast relays etc, with low current motors like the 25K motors you are running.

As I'm sure you know even low currents passing through low resistances will produce a tiny voltage drop. With low current motors the drop is too tiny to be worth bothering about.

You are absolutely right about the importance of a controller that feels just right to you.

You are also absolutely right about the importance of having the braids working properly. ( I might add getting tyres, gear mesh and bearings properly set up)

I reckon you'd be well advised to stick with the controller you like and if that last little bit of performance matters to you spend time tweaking the car.
 

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Oven only skimmed this thread but modern Mosfets I would have thought would have a lower ON resistance than most small relays unless you go to some pretty special relay. Find out what mosfet your controller uses and check the spec sheet, then check the conductor path including connectors etc a bit of de-oxit or inox always helps conductivity of connectors. The mosfet resistance is usually very low especially when used in parallel and if the PWM isnt going to 100% duty cycle then that is a different problem or maybe a choke feature.
 

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........ modern Mosfets I would have thought would have a lower ON resistance than most small relays unless you go to some pretty special relay. .....
I've measured a variety of controllers with both relays and MOSFETs using the method I described in post #6. The lowest ON resistance ones which use relays and the lowest ON resistance ones which use MOSFETs have similar ON resistance.
The full power relays typically used are nothing special, we are talking £3 to £5 each from the major electronics stockists.

Theoretically it is possible to achieve even lower ON resistances but the advantage of this would be vanishingly small given that the resistance of the track wiring to the International standard for the higher powered stuff of 6mm2 (10 AWG) minimum. Of course the track wiring for low powered stuff will be a lot thinner than that.
 

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Im bewildered by the tiny Gauge of wire used in some plastic track systems.
Plastic track systems are designed for cars requiring much lower currents than the high powered stuff, so plastic systems only need a smaller cross section of copper to achieve a similar voltage drop in the track wiring.

Having said that there are issues with the wiring. Just look at loads of SlotForum threads about upgrading the wiring of plastic track systems: lots more threads where the originator mistakenly thinks they have a problem with their power supply when the real problems are track joints and/or wiring.
 

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Discussion Starter · #26 ·
Hmmm. One thing I hadn't considered in my RC vs slotcar power delivery analysis is... the resistance of the track wiring. There's a very good chance that the total series resistance in the power path of a slotcar far exceeds the resistance in the power path of an RC car. In the RC car, the batteries are connected via a few inches of wiring & traces, plus a few contacts. In a slotcar track, the electrons will likely have to travel several feet before powering a motor. I've run on a track that used marine batteries. For safety, the track owner put the batteries outside. The power path for this track was 10's of feet in length. He used heavy gauge wiring, but it wasn't enough. This would likely make the resistance of a MOSFET (or stack of MOSFET's) negligible, unless the track is wired with heavy gauge wire, and the motors are drawing a lot of current (1/24 scale metal chassis levels of current).

Re: tiny wiring on some tracks and/or sets.... You can get away with that if each tiny wire only carries power for one car. If you run the power for say 4 cars through one pair of 26 ga wires, you will have surging problems. However, I AM amazed at the small wiring (which powers all cars) on a Carrera D132 system.

Bottom line is, I'm no longer concerned over the slight power loss of the MOSFETs in my SCP.
 

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Discussion Starter · #27 ·
if the PWM isnt going to 100% duty cycle then that is a different problem
I don't think that's an issue with the SCP controller. At part throttle, you can hear a whine from the motor (presumably the PWM frequency, or harmonic thereof), which disappears at full throttle.
 

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Best to improve anything you can, I wouldnt worry about the ON resistance of the Mosfets unless you find out that the particular model used is not of a low ON resistance spec. I upgraded the wiring in the CU and connection track of my Carrera D132 and analog systems, in my experience such a small conductor size will only cause problems. The analog controllers are also due for an upgrade but you need to start somewhere.
 

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Slot King
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voltage drop in the track wiring.
Track wiring is the same for everyone, in the context of the OP, not that relevant. However, choosing the wrong controller (one with high ON resistance) means losing out against the other competitors, therefore knowing this factor for the controllers on the market would help make the correct decision.

Joel
 

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Agree with what you are saying but If there are major problems with the track wiring then the resistance at the MOSFET becomes less proportionate to the overall track resistance, (a crude) analogy might be like putting a sports air filter on a car that isnt firing on all cylinders.
 

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Discussion Starter · #31 ·
Best to improve anything you can, I wouldnt worry about the ON resistance of the Mosfets unless you find out that the particular model used is not of a low ON resistance spec. I upgraded the wiring in the CU and connection track of my Carrera D132 and analog systems, in my experience such a small conductor size will only cause problems. The analog controllers are also due for an upgrade but you need to start somewhere.
Small conductors are only problematic if they carry power for more than one car. An analog track can be wired such that that doesn't happen. In digital, that's impossible since multiple cars can run on a single lane. In which case, large conductors are in order.
 

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The conductors on Carrera (both analog and digital) are smaller than you might think. I wouldn't want to run anything but a very low powered car on them. Looks like some pedantic production cost cutting exercise to me.

Best practice for low resistance is to continue appropriate sized conductors through the entire power distribution as well as paying attention to connector condition. Small conductors should be as short as possible. I've had to fault find too many power systems and its best to avoid problems if you can. These things often make more difference than you might think.

Another thing is that if your wires to your power source are too long and under sized, then you will probably be suffering surging when your race mate is opening the throttle down the straight.
 

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Alan Wilkinson
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Happy to report that I followed the instructions on the slot.it website to create a relay bypass for the SCP2 Metal.
I have track tested the solution and found it to be positive. It certainly did not have any negative effects.
Subjectively, The car felt as though it had a little more "urgency" about it under acceleration compared to my memory of the same car about 6 weeks ago.

None of the other functionality of the controller was compromised. Braking and all other functionality were unaffected.
The race car for the night was an NSR mosler, lightweight body, blue chassis with a long can King25 motor.
I have not bench tested the solution with a dvm and resistive loads.

I opted to install the relay in a small plastic project box about 6 inches from the be546 plug.
The controller's wires go into the box at one side and a new short set of three wires go from the box to the plug.
A domestic screw down connector inside the box is used to lock down the connections.
A very thin single core cable runs from the Metal cartridge relay trigger point to the relay box.

The relay can be heard to kick when bench testing the controller but on the track, the relay is not heard over the general ambient noise and the sounds of triggers reaching their end stops during the race.

Note that in linear mode 2 , so called "kids mode" , with the top switch in the "slow" position, the relay does not engage, irrespective of the curve/max setting.

The relay used is a coil relay (not a solid state relay) rated at 20 amps at 12v.

Alan Wilkinson.
 

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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......
Happy to report that I followed the instructions on the slot.it website to create a relay bypass for the SCP2 Metal.
I have track tested the solution and found it to be positive. It certainly did not have any negative effects.
Subjectively, The car felt as though it had a little more "urgency" about it under acceleration compared to my memory of the same car about 6 weeks ago......
Interesting comparison with 25k motors - bemoore doesn't detect a difference yet Alan does. Of course some 25k motors take more current than others. How much voltage drop you'll get depends on the current and the ON resistance (not the manufacturer's claimed revs). Another part of the explanation may be bemoore's analogue controller has less full power resistance than Alan's SCP. The more ON resistance you've got the more benefit you get from eliminating most of it with a relay.
The high end controllers I've measured have sufficiently low ON resistance so that the relay doesn't make a noticeable difference with even the highest current 25k slot car motors. (The relay does make a noticeable difference with really high current slot car motors). So it seems the SCP does have a higher ON resistance and/or Alan is a better than me at noticing small differences in how the car feels.
 

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The relay used is a coil relay (not a solid state relay) rated at 20 amps at 12v.
Good choice!
High end controllers typically use either a coil relay or design their own circuit using really low on resistance MOSFETs - I don't recall seeing one with a solid state relay.
Looking through the spec sheets for lots of solid state relay they have a lot more on resistance than the sorts of relay used for blast relays or the MOSFET full power circuits used on some controllers........and these solid state relay aren't cheap either. If you want techy details, the "zero crossing" ones designed for AC won't work on normal slot car tracks (which are DC). I don't know why the DC ones don't use the sort of low resistance circuits the controllers use, but the spec sheets show they don't.
Sure I could write a long list of reasons why solid state should be better. However so many of these controller makers choose coil relays, surely their designers must know quite a lot about electronics to design the rest of the circuit!
 

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Alan Wilkinson
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Interesting comparison with 25k motors - bemoore doesn't detect a difference yet Alan does. Of course some 25k motors take more current than others.
Did Beemore make the change to add a relay?
I did not see that in this thread.
In a few weeks time I will be able to test this on NSR-King 30 and scaleauto sc25 "outlaw".

Alan
 

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Did Beemore make the change to add a relay?
I understood (rightly or wrongly) he didn't detect a difference with or without the relay using his "good analog controller" , not sure if he's added a relay to his SCP..
Many controllers with blast relays have a switch to disable the relay, this can be needed for some sorts of choke function. That switch makes it very easy to compare how a car feels with and without the relay working.
Some high end controllers have choke cuircuits which disable the bast relay when necessary, so their designers don't see the need for a separate switch.
 

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Rich Dumas
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Adding a full speed relay is not likely to do anything for you if you have a controller like a Parma Turbo with contacts that make when you pull the trigger all the way. My 1/32nd controller is a Difalco Genesis and that has a bypass relay located at the hookup end of the lead wires. That arrangement eliminates the resistance of the lead wires and makes using very heavy wires between the handle and the electronics unnecessary.
The advantage to a solid state relay would be that it has no coil to load the control circuit. Relays of that sort were used as track power relays in race management systems that used printer ports. I am not certain that a solid state relay will not drop at least some voltage.
 

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Discussion Starter · #39 ·
Did Beemore make the change to add a relay?
No. I used an SCP1 controller with standard analog cartridge (no relay), and a One Stop analog controller, which has metal contacts inside the controller housing for full power.
 

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Bypass relay at the hookup end is smart. Designers (not specifically for slot cars but more broadly) often like sticking with a feature or a signature design point that they know works and has a following I’m not surprised if bypass relays are still a thing in new designs even if a few Mosfets would do the same job for a bypass or control curve feature. Also sections of the market may not want to change too much if they know a certain feature (e.g bypass relay) still works well for them. An example in 1:1 sports cars might be buying a new lotus for the H pattern gear shift as a matter of preference over a paddle shift equipped vehicle.
 
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