19 replies to this topic

[CDavis7]

Has anyone ever tested how many amps an RH motor draws the instant full power is drawn?

I know theyre low amp motors but Im wondering how much headroom they need

[Racer36]

Not very scientific , but I saw between 5 and 6 amps on the power supply on a friends track . One RH powered flexi when the power came on.

[Don Weaver]

Doubt slot racers have an instrument that responds quick enough to record inrush current at start.  Not sure about these type of motors but 7 to 8 times nameplate current is a common estimate.

[havlicek]

Doubt slot racers have an instrument that responds quick enough to record inrush current at start.  Not sure about these type of motors but 7 to 8 times nameplate current is a common estimate.

 

Yep...and to confuse things even further, the current draw will be affected significantly by the load the motor is under.  Different gearing, chassis will make the same motor draw different amounts of current.

[CDavis7]

Thanks to everyone who commented so far. This is for a project Im working on.

Most power supplies are designed with fail safe circuitry which limits how much current a motor can draw at startup. I need to know how many amps a battery should have to not starve a motor of current at startup.

[CDavis7]

I might just put a big cap in my circuit instead. 🤔

[NSwanberg]

Has anybody ever used an amp recording strip chart for the amp draw of a slot car running several laps at speed? It might tell a lot about what a power supply can actually deliver.

[Ramcatlarry]

I tested track wiring with a 'clamping amp meter' which can display and hold peak info digitally.  That kind of meter can lock on a nanosecond of draw.  Group-7 and euro class motors can show over 40 amps EACH.  Problem is that data is really meaningless.  Maximum amps is when the armature wire smokes.

 

A typical commercial rental/flexi track should have about 10 amps PER LANE of power available in the power system - the transformer and wiring. Average braid is equal to a #12 ga wire as should the track.  If you regularly race faster stuff, the amps per lane should double, with the braid being the 'choke'.

[zipper]

Group 7 cars draw average almost 40 amps - insane! Our power pack has an accurate digital meter.

[CDavis7]

I tested track wiring with a 'clamping amp meter' which can display and hold peak info digitally.  That kind of meter can lock on a nanosecond of draw.  Group-7 and euro class motors can show over 40 amps EACH.  Problem is that data is really meaningless.  Maximum amps is when the armature wire smokes.
 
A typical commercial rental/flexi track should have about 10 amps PER LANE of power available in the power system - the transformer and wiring. Average braid is equal to a #12 ga wire as should the track.  If you regularly race faster stuff, the amps per lane should double, with the braid being the 'choke'.

Thanks Larry. This is what I was looking for and its helpful.

Much appreciated

[Ramcatlarry]

Group 7 cars draw average almost 40 amps - insane! Our power pack has an accurate digital meter.

No, they should not have that high of "AVERAGE' amp draw. the analog meter may swing that high, but the duration of draw time is only an PEAK instant.  Load (amps) vary constantly over operation time in electric cars as do gasoline engines vary fuel flow over throttle position and other loads.

 

Capacitors can provide an instantaneous amp discharge quicker that a transformer can ramp up the amps.  The response time for a chemical battery in somewhere in the middle of that discharge time in nanoseconds. On a dragstrip the first car to accelerate gets all of the capacitor load unless EACH lane is an isolated circuit.  I proved to myself that a charged capacitor alone will NOT power even a Falcon-7 the length of a 1/4 mile dragstrip.

[havlicek]

 

zipper, on 15 Jun 2019 - 1:42 PM, said:

Group 7 cars draw average almost 40 amps - insane! Our power pack has an accurate digital meter.

No, they should not have that high of "AVERAGE' amp draw.

 

 

I think what Pekka meant is that "on average" they can draw that much for an instant...meaning that the average G7 car can draw that much.  Not all G7 cars (*or any cars for that matter) are the same.  Pekka is knowledgeable about this stuff, so I think that's what he meant.

[NSwanberg]

No, they should not have that high of "AVERAGE' amp draw. the analog meter may swing that high, but the duration of draw time is only an PEAK instant.  Load (amps) vary constantly over operation time in electric cars as do gasoline engines vary fuel flow over throttle position and other loads.

 

Capacitors can provide an instantaneous amp discharge quicker that a transformer can ramp up the amps.  The response time for a chemical battery in somewhere in the middle of that discharge time in nanoseconds. On a dragstrip the first car to accelerate gets all of the capacitor load unless EACH lane is an isolated circuit.  I proved to myself that a charged capacitor alone will NOT power even a Falcon-7 the length of a 1/4 mile dragstrip.

 

ergo a strip chart recording could prove to be very interesting. I am working on it.

[zipper]

Our industrial grade power pack with digital V/A metering outputs 400A@10V and 300A@16V. Running eight G7 cars the meter shows constant over 200A and peaks upto 290A on pretty heavy glue condition. So let's say 30+ average and 35 peak average. Never checked when qualifying...

[havlicek]

For the most part, this all is mostly academic.  It's interesting for sure, but "where the rubber" meets the road, not really useful for racers.  I guess it could be for track owners who may have underpowered their tracks???

[CDavis7]

Larry (ramcatlarry). Im trying to determine if a battery, of sufficient amperage, or a capacitor is better for not choking a hawk motor on a test bench. My current power supply seems to have sufficient amperage but its internal circuitry shuts it off if I try to start a motor at full power.

Btw- the motors being tested are mules and not intended to be raced after such abuse

[Ramcatlarry]

A capacitor can store and discharge a voltage.  It cannot store much WATTAGE, although a 3 Farad cap can store a lot more than a 1/2 Farad one, it still cannot make a falcon motor run a lap on a track by itself.  The auto/truck battery is usually rated by Amp-hours of 500 to 1500 amp-hours.  A 500 AH battery can discharge one amp for 500 hours or 100 amps for five hours.  Most power transformers will provide amps at a slower (choked) response rate than a battery and can show a lowered voltage when the amp draw exceeds their basic rating.

 

clamping amp meter:  https://www.grainger...df/20E890_1.PDF

[NSwanberg]

It might even be more interesting to record voltage and amps on the braking circuit for all the lanes during several laps at speed.

[MSwiss]

Nelson,
When Lee Gilbert had his King, in the early 90's, Alex Danilchek went around the track with an oscilloscope, and measured amp draw, so he could provide Lee with enough switching power supplies to adequately power the track, as it was the first "serious" track of that era to ditch the batteries, and go full power supplies.

IIRC, they said there was 100 amp spikes when a G7 car was pulling out of the glue, in the 90, on Red.

That was the track, where at his first big race, while standing at the end of the straight, watching Lee qualify, I got "shot" in the chest by a segment of Lee's comm.

Everybody thought I was clowning around, as I jumped away, as the motor blew.

I walked around to the end of the bank, to Lee's car, where it had free-wheeled all the way around ,to.

I turned it over and announced "Lee, your comm is missing".

It literally looked like someone had photoshopped the comm out of the motor.

Where the comm had been, all that was there, was a bare armature shaft.

I walked back to where I was standing, and there was a comm segment, (lightly) melted / stuck to the carpet.

[NSwanberg]

I've gone modern. The old Silk 7 power supply amp meter  gave out and it was not very precise anyways.

 

Regulated is nice. It stays at 7 volts while running 3 different motors at the same time.

 

No problems so far but the manual came written in Spanish.

 

53 bucks at Amazon.

 

https://www.amazon.c...0?ie=UTF8&psc=1

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