Motor voltages and currents
- Thread starter MickyF
- Start date
Greg Elmassian
Guest
motor current depends on a lot of things, load mostly. Unless you are running teeny motors and locos, build something that will handle 5 amps and 24 volts.
Greg
Greg
GAP
G Scale Model Trains, 1:1 Sugar Cane Trains
The DRV8871 is rated at 3.6A Peak and 6.5V to 45V so current draw should well be below 3.6A, about 2A should give a bit of headroom for variations.
What type of engine are you planning on using?
22V Lipo should be OK as it is in the middle of the voltage range.
I would start by asking what make of models you will be using? - Then we will know the motors..
Then what type of line do you want to model? - A bucolic British branch-line, will nor need a 6S Lipo! An express main line might?
Also, beware of the sort of 'punch' available from a bunch of Lipo batteries.. You need to have some serious protection built-in to your system.
Then what type of line do you want to model? - A bucolic British branch-line, will nor need a 6S Lipo! An express main line might?
Also, beware of the sort of 'punch' available from a bunch of Lipo batteries.. You need to have some serious protection built-in to your system.
Thanks Greg, maybe the driver I'm planning to use is not man enough then as it's max current is 3.5 amps. Perhaps I should use an ESC
The Newqida loco is stripped down and now I've done some tests (on the bench). I simulated a load by friction on the wheels. No load at 10v approx .5A, loaded approx .8A. Slowest speed seems to be at about 2 volts. The battery that came with the train is 7.2v 2000mAh and I think I'm happy with that - at 10v it looked like the wheels were going to fall off! I should get 4 hours running maybe - the grandchildren will be bored by then! Now I'll order the DRV8871 motor driver board as that is 3A.
Greg Elmassian
Guest
Yep, the Newquida motors are on the small side, and also remember that the AVERAGE current you are reading does not belie the short term spikes. Also worst case current is measured by actually stopping the motion of the wheels at full voltage BUT this can damage some inexpensive drives/gears.
So, for lightweight locos with small motors and not a lot of load, that driver seems ok, I agree.
Greg
So, for lightweight locos with small motors and not a lot of load, that driver seems ok, I agree.
Greg
I did try and stall it but my bench power supply has a 2A current limit. You're right about the current spikes and the scope picked up voltage spikes, probably why there is 10mfd across the motor terminals. I'm going to keep the arduino well away from the motor controller! I think the controller board has quite good protection -we'll see!
Greg Elmassian
Guest
there is really a 10 mfd cap across the terminals? a non-polarized electrolytic? hmm.... what is the voltage rating? That is a noise cap, by the way, not helping motor, but reducing electrical interference to other things.
Greg
Greg
In all my career as an electronics engineer I've never seen one of these caps! You learn sommat every day... Don't know a lot about motors - it's my first experience with them apart from model boats. And I know just about nothing about trains! But learning fast and keen on the control side of everything. Great to do some programming again and beginning to fall in love with the Arduino.
Greg Elmassian
Guest
common, but if it is not huge, it must be pretty low voltage, as I have stated on another thread, take it off.
Greg
Greg
Rhinochugger
Retired Oik
Yes, in my youth (a long time ago) these were referred to as TV suppressors and very common on model locomotives; I s'pose because they were nearly always going to be used indoors
It's def snipped off - and it's 50v by the way. This had max 7.4 volts across it. I think dunnyrail was running much higher voltage when it caught fire!
Greg Elmassian
Guest
if it was 50v, it must have been closer to 1 microfarad, 10 microfarad at 50 volts and npo is normally big, did it really say 10 mfd, or did it just have a 10 on it?
Greg
Greg
?? Not very big at all. ??
Assuming 'mF' is micro-farad, and NOT milli-farad.
10uF 63V 6.5 x 11 mm.
Once they dry-out, and go 'pop' a little like a confetti-cannon!
Yes - a couple of my apprentices years ago spent their lunch times ramping them up way above their voltage until their was a confetti type explosion! Scared the living daylights out of the gals on the production line! We used to use thousands of them 10 microfarad 63v and the miniature ones (like the one on the train) were cheap as chips. The bigger smoothing stuff for PSU's could be huge! Think the ones in my racks are way out of date now!?? Not very big at all. ??
Assuming 'mF' is micro-farad, and NOT milli-farad.
10uF 63V 6.5 x 11 mm.
Once they dry-out, and go 'pop' a little like a confetti-cannon!
Greg Elmassian
Guest
That link had 10 mfd npo at 5mm by 11 mm.... I think yours are much smaller, how big was it Micky? That size or a lot smaller? (I'll bet smaller)...
Here is a pic of my infamous capacitor! Metric scale on the ruler.
Back to the original question:
If you are using the original motor, then feed it with around the 7.2V that the six-cell Ni-Cad battery pack would give it.
Personally, I would continue to use said Ni-Cad pack, until it died. Then replace with either a six-cell, 7.2V NiMH pack, OR a 2S Lithium pack.
The motor-shield you are considering, should be adequate for this particular loco, or other similar single-motor models. - Especially the likes of the smaller LGB offerings, the Buhler motor's are very good.
If you are using the original motor, then feed it with around the 7.2V that the six-cell Ni-Cad battery pack would give it.
Personally, I would continue to use said Ni-Cad pack, until it died. Then replace with either a six-cell, 7.2V NiMH pack, OR a 2S Lithium pack.
The motor-shield you are considering, should be adequate for this particular loco, or other similar single-motor models. - Especially the likes of the smaller LGB offerings, the Buhler motor's are very good.
Greg Elmassian
Guest
OK, then that is as I asked, the same size about 5 x 11 mm, so indeed the common size for a 10 mfd, npo electrolytic.
I agree with Phil, keep the voltage near the original. Some of the advice above implies you can lower the voltage with settings, but all of this equipement is PWM, pulse width modulated, which means you control speed and "voltage" by varying pulses of FULL VOLTAGE, as these circuits are just an on off switch with varying "on" times.
The point here is that using a much higher voltage and then narrowing the pulses on time way down is not the same as longer pulses at lower voltage, you can get heating and other unwanted effects when there is a gross increase in voltage.
Greg
I agree with Phil, keep the voltage near the original. Some of the advice above implies you can lower the voltage with settings, but all of this equipement is PWM, pulse width modulated, which means you control speed and "voltage" by varying pulses of FULL VOLTAGE, as these circuits are just an on off switch with varying "on" times.
The point here is that using a much higher voltage and then narrowing the pulses on time way down is not the same as longer pulses at lower voltage, you can get heating and other unwanted effects when there is a gross increase in voltage.
Greg