Battery RC and two motors

R

Robert Howard

Registered
Does anyone have any advice and experience of doing battery RC conversions of locos with two motors?

Does not look straight forward to me, as you need to make sure each motor gets enough amps and volts...

I would guess the current draw would be much higher, so a single AA battery NiMH pack would struggle?

Would it perhaps be best to have a separate battery and ESC for each motor, and split the signal from the reciever?

Cheers
 
I feed both motors from the same supply.
They each get the same voltage etc.
I use this with 2 x Essel units, on 2 separate locos and it works for me.
Typically 16 x AA NiMH cells = 19.2V. Each Essel chassis is 12-24V.
A single ESC such as Electron supplies both motors.
Also used a Brian Jones MAc 5.
If you drop the battery voltage down to 14.4 then a Viper will do.
 
Hi, so first I am not the expert.

But no it's not that complicated. Just size the batteries and the ESC to the job (total two motors) . Yes maybe a beefier spec for both, but a two motor loco probably has more space anyway. Then just split the motor out of the ESC in parallell. It will work fine.

Having said that i have a Garratt and i wanted to avoid cables connecting either end. Here I just have separate ESCs and two batteries on one 2.4g controller (RCS)
 
Yeo I agree with already been said, either choose one suitable esc to run both motors or use one esc per motor block.

Both methods work well, but if your using 2 esc 's makes sure there the same brand so they behave the same, or they might have slightly different running characteristics

Dan
 
Thanks all

My worry was that, if I put the motors in parallel, the amps will be halfed and I read somewhere that AA NiMH cells were limited in what amps they could push out.

Does not sound like this is a problem :-)
 
If the two motors are in parallel then yes, they will consume double the amps of a single motor - but if you're talking about LGB Buhler motors (in good condition) then that's still only around 1 amp total under normal loads (half an amp per motor).... if you're using other motor types which may be more power-hungry and less efficient, then you will need batteries and a speed controller that will handle whatever total they draw. Unless you have a special need for two separate systems like Cogges' Garratt example, I would certainly try to use a single controller and a single battery pack with enough amp-hours in it for the sort of running time you want - a 1.5 amp-hour battery pack would (on paper) run a twin-motor LGB loco for around an hour and a half, for example.

Jon.
 
If your interested an lgb white pass alco will haul 25 bogie wagons on the flat with r 5 curves, for 2.25 hours with a sub c 3000mah pack using an rcs omega esc. Before even slowing timed laps. Which is a practical proof of Zero's maths i guess when adxing a heavy train ;D
 
CoggesRailway said:
If your interested an lgb white pass alco will haul 25 bogie wagons on the flat with r 5 curves, for 2.25 hours with a sub c 3000mah pack using an rcs omega esc. Before even slowing timed laps. Which is a practical proof of Zero's maths i guess when adxing a heavy train ;D
Click to expand...

Well, there we go then! ;)

It's always good when the theory is supported by practical experience..... :)

Out of interest, what voltage was the sub-C pack in this case?

Jon.
 
CoggesRailway said:
If your interested an lgb white pass alco will haul 25 bogie wagons on the flat with r 5 curves, for 2.25 hours with a sub c 3000mah pack using an rcs omega esc. Before even slowing timed laps. Which is a practical proof of Zero's maths i guess when adxing a heavy train ;D
Click to expand...

Which, if it was to exhaustion, gives you a draw of a bit over 1.3 amps. That sounds about right and is well within the 0.5C of the battery (1.5A for a 3000mAH battery). For those new to the battery world, it is generally recommended that batteries not be discharged (or charged for that matter) above 0.5C. BTW, I'm getting a very similar outcome from my Piko BR204.

The voltage is fairly irrelevant; motor and hence loco speed will be governed by the voltage supplied but not the "pulling ability" which is governed by the current the battery can supply and the motor can use (and the adhesion weight but that's not a directly battery related issue). Of course the starting voltage, the voltage at which the loco will move, will change depending on loco and train weight, the internal (physical) resistance of the gear train etc, and motor characteristics (and indeed the characteristics of the rest of the electrical circuit but losses there should be minimal). But in most cases this should be less than about 4v for converted commercial RTR products when light loco, which can be supplied by anything more than 3 or 4 NiMH or NiCd batteries (which deliver a nominal 1.2 volts per cell).
 
I have a 3 truck shay with 3 motors running off one ESC the main criteria is to make sure that the ESC can supply the current.

For mine I used a 10A ESC used primarily in robots so it is designed to run multiple motors.

It uses a standard 2.4GHz hobby remote transmitter and receiver.

I made a 14.4V x 5400mAH battery pack by making up 2 x 14.4v x 2700mAH batteries and then wiring them in parallel.

Batteries in series increase voltage, batteries in parallel increase capacity just make sure if wiring in parallel the voltage is the same in both battery packs.

Out of interest the shay runs for about 3 hours on the battery, when I used only one pack the running time was about half that time, the ESC has a regenerative function in that when the loco is coasting energy is returned to the battery.
 
The LGB loco mentioned above is nominally 14.4v (two "tamiya" race car packs) but it actually gives about 17v in reality.

In regard to the battery above (GAP) I have a similar pack in a loco and was advised on here to diode protect it. This means they cannot discharge into each other but can discharge in parallel and charge separately.

Does your set up do this, or was this over engineering?

Ian
 
Hello Ian.
My experience has been that a diode is needed on each pack to prevent the possibility of one pack discharging into another. If a suitable Schottky diode is used, the voltage drop will only be about .2 of a volt.
Yes 14.4 volt packs can read 17.0 volts when freshly charged. They will hold that extra voltage for only a short while before they discharge to near the nominal voltage which is held almost until the battery is discharged.
 
Diodes in batteries wired in serial is a very good idea. One faulty cell can make the other pack try to recharge that cell and can cause an overheat to the point of fire.
Just a note - it is outside of toy safety regs to have batteries in series under any circumstances - not that that matters here, but it shows the problem.
 
stockers said:
Diodes in batteries wired in serial is a very good idea. One faulty cell can make the other pack try to recharge that cell and can cause an overheat to the point of fire.
Just a note - it is outside of toy safety regs to have batteries in series under any circumstances - not that that matters here, but it shows the problem.
Click to expand...

Do you mean in parallel?
 
oops - yes? Thanks.
 
Tony Walsham said:
Hello Ian.
My experience has been that a diode is needed on each pack to prevent the possibility of one pack discharging into another. If a suitable Schottky diode is used, the voltage drop will only be about .2 of a volt.
Yes 14.4 volt packs can read 17.0 volts when freshly charged. They will hold that extra voltage for only a short while before they discharge to near the nominal voltage which is held almost until the battery is discharged.
Click to expand...

Tony,
A couple of questions.

I do not have any diodes fitted but from what I have just read that sounds like a good idea where are they fitted and with what polarity?

Will any diode do or does it have to be a schottky?

I was just going to treat the pack as just one big battery.
 
GAP said:
Tony,
A couple of questions.

I do not have any diodes fitted but from what I have just read that sounds like a good idea where are they fitted and with what polarity?

Will any diode do or does it have to be a schottky?

I was just going to treat the pack as just one big battery.
Click to expand...

Forget the diodes GAP. Despite all the recommendations here, they really aren't necessary. I've never used them for paralleling either NiMH or LiPo. All they do is make charging difficult.

The respondants here seem to think that if a cell fails to short circuit in one parallel arm, the other arm will feed into it. How many cells have you had fail to dead sort circuit?? I never believe unless I can test for myself.
If you want, try an experiment. Take a string of cells, with one completely discharged (a much more likely scenario than a dead short), then parallel another set which is complete, and measure the current that flows.
 
I don't want to get into the argu disagreement about this..

I reckon a polyfuse in each battery feed would be a better idea for protection?? - I would be much more worried about the potential (sorry!) for a short 'somewhere' and the current that could then flow..
 
I am talking NiCd or NiMh. I have no idea about Li-Ion or LiPo. For the cost of two diodes, about 40c total, you will have peace of mind it cannot happen.
Any diode will do. A Schottky minimises the voltage drop from .7 of a volt to .2 of a volt. Banded ends away from the battery packs.
By all means add a Polyswitch as well for overall battery and wiring protection.
 
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