[HELP] Power Functions Reciever V1 or V2

[1974]

Two Ms are often used in the train world. Now that will only be possible with a V1 reciever

Since Ls are more powerfull than Ms and can function on a V2 channel just what is going on inside the Ms?

Where's Philo and his big hammer?

[PhyBuilder]

I actually tried it myself now. There is indeed an issue. Even more strange: although reproducable, the issue occurs intermittendly. I connected three mediums onto a V2, and sometimes they work, but mostly I need to switch directions or try different combinations to have them run all at once. When some of them don't run, a beep sounds. I was unable to find a reproducable correlation to either stalled, idle or loaded motors.

Addition: discovered the following reproducable behaviour and thus facts:

- The problem depends on the limit per output port, not per receiver. Two mediums work fine when connected to different outputs.

- Two XL Motors work fine, regardless whether connected to separated outputs or sharing one

- The beep sound comes from the medium motors themselves, and shows that the already mentioned startup current can't be delivered. The total peek-mA delivered by the V2 is insufficient to overcome the initial magnetic resistance.

Edited May 19, 2014 by PhyBuilder

[1974]

Thanx for the effort

So the scientific answer is this :

Cheers,

Ole

[Blakbird]

From what I understand, the problem is not so much with the receivers as with the resistors in the M-motors. So the fix may actually be to change the motor, not the receiver.

[1974]

Resistors? As in PTCs?

[PhyBuilder]

@ BB: Thats my conclusion too.

Edited May 19, 2014 by PhyBuilder

[Nazgarot]

The design of the M motor allows it to pull a lot of current on startup due to a "large" capacitor on the engine coils. For V1 this is not a problem as it doesn't give that much current being limited by it's high internal resistance. The V2 however with its very low internal resistance is able to deliver a very high starting current to the capacitor, and will trigger the over current protection of the receiver. This is basically a filter (RC). The capacitor will retain some charge (it slowly discharges through the circuit) from each attempt to start, and by toggling the motor on/off a few time it may have a high enough charge that the start current comes below the overcurrent limit of the V2 receiver and it manages to start the motors running. But as soon as the capacitor is discharged enough the starting problem will reoccur.

I can't say why Lego has such big trouble replacing the M-motor, but it may simply be that they have a lot of "old" M-motors they need to get rid of, and not many are being sold as there is no new models with the M-motor (and they will probably not launch any because of the trouble combaining it with V2 receiver). I believe the only way the "old" M-motor is sold is through the PF add-on package.

To sum up:

V1: Anything without a high torque requirement, or M-motors.

V2: Anything without a M-motor.

Hope this helps.

-ED-

[1974]

It sure does! Makes sense then, but the problem will be there for years to come as there are so many old Ms out there

[Speedster]

It sure does! Makes sense then, but the problem will be there for years to come as there are so many old Ms out there

But I guess also a lot of V1 receivers to work with M motors. And as Nazgarot said for everything else the V2 and likely a new M motor.

[Philo]

Nazgarot perfectly summarized the problem. Note that ONE M-motor on a V2 output is generally safe. Problem begins when you attach 2 M-motors on a single output.

Edited May 20, 2014 by Philo

[1974]

Yes, but TLG could have upped the output resistance of V2 so that driving the Ms' caps wouldn't be a problem. Of course it depends on just how much were talking about here. Anyone know the output resistance of V1/2 and the size of the cap in the M motor?

[Philo]

I tried that route but it doesn't work with reasonably sized resistors. V2 output current can reach 2A and over current protection (that causes problem here) is around 3A. We can say that the problem is that the V2 motor driver is at the same time very good... and a bit picky! Capacitor in M-motor has a value of the order of 1µF.

[1974]

1uF? That's rather high. It boggles my mind that TLG didn't try the V2 with two Ms, it's a common configuraton. Or maybe they did aand don't care

Can't seem to find anything in the datasheet about maximum capacitve load