# Current draw?



## AcesFull (Jan 6, 2008)

Is there a general number to consider as far as current draw from these little HO cars? I have a 24VDC 12A supply that is not variable. I am going to add independent variable circuits to each lane fed from the main supply and want to make sure I spec out my components correctly. I've read anywhere from 1 amp to 5 amps per lane. Any insight is appreciated. Thank you.


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## Pete McKay (Dec 20, 2006)

Contact Scale Auto and get the variable voltage 2 amp G-Jet power pack. I ran a 4 lane oval with magnet cars last summer and had no problem with power surges or over heating, and it have 12v-9v-7.5v-6v-4.5v and 3v settings. So it can be used for everything from all out racing to breaking in motors. You can cut the voltage down for the kids, and honestly I didn't see much of a perfomance differance racing SG+ cars at 12v as opposed to 18.5v. And the best part is they're only $25.


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## Grandcheapskate (Jan 5, 2006)

I commonly read that 1 amp per lane is fine if you are using stock cars - whether they be T-Jets or magnet cars. I would not go with 24 volts however. The track I built at my parents house for use when I spend time there, uses old Aurora 22v power packs. I am finding that 22 volts is too high; although I do need to try a variety of controllers with different ohm ratings. Maybe with the right combination of voltage and controllers, 22v is acceptable.

Joe


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## tasman (Feb 17, 2007)

Pete McKay said:


> Contact Scale Auto and get the variable voltage 2 amp G-Jet power pack. I ran a 4 lane oval with magnet cars last summer and had no problem with power surges or over heating, and it have 12v-9v-7.5v-6v-4.5v and 3v settings. So it can be used for everything from all out racing to breaking in motors. You can cut the voltage down for the kids, and honestly I didn't see much of a perfomance differance racing SG+ cars at 12v as opposed to 18.5v. And the best part is they're only $25.


Pete, can you estimate the difference between running at 12v vs. 18v - 10%, 20% etc. Most posts I've read relating to power supplies seem to advocate 18v, 20v and more with at least 2 amps per lane.

I have a 70 ft 2 lane track currently powered by 1 18V wall wart per lane. I run Tomy SRT, Tyco, Magna-tractions and a few T-jets. I would love to be able to use 1 G-Jet power pack per lane.


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## AcesFull (Jan 6, 2008)

Grandcheapskate said:


> I commonly read that 1 amp per lane is fine if you are using stock cars - whether they be T-Jets or magnet cars. I would not go with 24 volts however. The track I built at my parents house for use when I spend time there, uses old Aurora 22v power packs. I am finding that 22 volts is too high; although I do need to try a variety of controllers with different ohm ratings. Maybe with the right combination of voltage and controllers, 22v is acceptable.
> 
> Joe


My main supply is 24VDC 12A. I am not powering the track direct with this. I am using it to feed for circuits containing LM338's for 0-24VDC variability and 5A capability to each lane independently. I already have the supply and have gotten samples of the main components in the sub-circuits. Sounds like 5A rating is sufficient, now time to build.


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## martybauer31 (Jan 27, 2004)

5A is plenty, I have a 4 laner and it will run G3 Super STocks with no issues whatsoever.


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## micyou03 (Apr 8, 2003)

I'm running three amps for two lanes and it seems tobe plenty.


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## Pete McKay (Dec 20, 2006)

Tas, we ran low power arms with polymer magnets in inline motored SG+ cars. The 12v 2 amp powerpack pulled all 4 lanes without a blink using Parma 75 ohm controllers. The track originally had Tyco 18.5v wall packs, one per lane. Times before and after the change were virtually non-existant and the cars ran cooler on longer races. We cut our failure rates in 1+ hour enduro's in half. With pancake motors the cars also seemed to be better as well. 

I have read the suggested minimums regarding amps, unless you're running a balls-out neo car you don't need more than 1 amp per lane IMHO. Others are better educated to answer that for sure but in my application the single 2 amp power pack worked just fine.


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## AfxToo (Aug 29, 2003)

AcesFull, you are fine with what you got setup. 

With unlimited current available from the power supply and assuming losses from wiring, electrical contacts, motor brushes, etc, the max current draw will be power supply voltage divided by the armature resistance. Most stock and super stock arms are around 6 ohms (LL T-car arms are around 4 ohms). So if you are using a 18V supply with 6 ohm arms the max current draw for each lane will be 3 amps. However, and this is a huge factor, this assumes the motor arm is not moving. 

Once the arm (or rotor) starts moving it is a voltage generator. The voltage the arm generates opposes the voltage produced by the power supply. The current in the circuit drops considerably because the current is now equal to the difference between the power supply voltage and the generated voltage divided by the arm resistance. Say for example the motor generates 12V. This would mean that the current draw is now 1 amp rather than 3 amps. With a typical stock Tomy or Tyco style stock/superstock car the current while running is less than 0.5 amps, so you can see the huge difference that the generated voltage causes. 

Again, this all assumes the power supply has an unlimited current potential. Lower end units and wall warts typically can't supply all of the current that is required under all conditions. Their true abilities are reflected in their power, or VA rating.

One take away from this discussion should be that you need to be very careful about situations where your car is getting power but the arm is not turning. Say a fur ball, carpet fiber, paint flake, or metal shaving gets into the arm and keeps it from spinning. If you hammer the throttle in this situation you arm will see the maximum current that I mentioned earlier (if the power supply can provide it and most wall warts can't) and you can quickly burn out the arm. Those tiny wires don't take a lot of abuse and will eventually melt. 

In any case where you are using anything other than a race set wall wart, make sure you fuse the track and every lane. I recommend a fast acting fuse on the main feed and DC marine style panel circuit breakers (not residential style AC breakers) for each lane. For your setup, a 10A main fuse and 5A breakers per lane would be good unless you want to go a bit lower per lane.


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## SwamperGene (Dec 1, 2003)

AcesFull sounds like a solid plan, you've got great power to start with. 

Just out of curiosity, how many who are running 4 lanes on 2-5 amps have had an opportuninty to try their same setup with a 10 amp or so unit. I used to have 21V 2.5A powering my track, and I too always said it was plenty. When I upgraded to 10 amp the difference in raw power the cars had was immediately noticable.


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