SBrick maximum amperage

[LEGO Train 12 Volts]

I don't know if this is the right area for this question but it seems to me that most sbrick users are here.

Since I'm converting my locomotives to Li-Ion batteries in combination with the electronic component MT3608 I wanted to know if any of you have experimented the use of two 10440 batteries combined with the MT3608 to power the SBrick (with 9 volt).

The milliamperage per hour of my 3,7 volt 10440 lithium batteries is 1000 mAh ... would the Sbrick support such a power supply, without burning?

Edited April 5, 2021 by LEGO Train 12 Volts

[Andman]

Maybe this thread helps: https://www.eurobricks.com/forum/index.php?/forums/topic/175279-operate-sbrick-plus-with-3s-lion-at-126v-max/

[MikeTwo9398]

I did use 3 LiFePo4 batteries and 3 spacers with a SBrick in my Baja Buggy.

The buggy has 1 servo, 1 LED and 2 Buggy motors (each on 1 port of the SBrick).
So far nothing got damaged.

Powering Locomotive motors will probably no problem. Just make sure the voltage does not exceed the 10.8 [V].

The only problem I encountered, was that not every battery box worked.

[pdw]

1000 mAh is a measure of battery capacity, so is not relevant.  What matters is the input voltage.  There's a definitive answer from one of the SBrick team on this thread on the SBrick forum.  Basically, 10.8V safe upper limit, 11.8V absolute upper limit.

So if you're planning to use 2 x LiIon cells and step up to a regulated 9V you should be absolutely fine, and could safely go a bit higher.

[LEGO Train 12 Volts]

On 4/1/2021 at 1:35 PM, MikeTwo9398 said:

Powering Locomotive motors will probably no problem. Just make sure the voltage does not exceed the 10.8 [V].

 

On 4/1/2021 at 2:51 PM, pdw said:

1000 mAh is a measure of battery capacity, so is not relevant.  What matters is the input voltage. 

Thanks for the answer, the mAh are not relevant but the amperage do ...so I was wondering how many watts the SBrick supports, but this is an information that I haven't found ... everyone is talking about maximum voltage but the voltage is only part of the formula W=VxA ...if I powered the Sbrick with 9 volts and 20A I bet it would burn out! 

[pdw]

You can't power something with 20A;  you can connect it to a power supply capable of delivering 20A at 9V, but that doesn't mean it will draw 20A. The current draw depends on the load.

The SBrick has overcurrent protection and thermal protection.  I think the overcurrent protection is set at 3A per channel, which would mean 12A in total, although actually drawing this would trip the thermal protection very quickly.

A PF train motor draws 1.3A @ 9V when stalled, and much less in normal usage, so you unlikely to trigger the overcurrent or thermal protection, even with several motors connected.

[Toastie]

Hi Emanuele,

as @pdw said, you can't power a device with 20A ... you can only offer it ...

All these batteries/rechargeables have a certain internal resistance, limiting the maximum current you can draw, regardless of the external resistance (make that zero, not realistic, but); as the latter is always in series with the former, the internal battery resistance is also always the maximum current delimiting value. The maximum current delivered by 10440 LiPos is about 700mA. Make that 1A, but I doubt that. 6 of them in series does not change the max. current: It will be still 1A. Your deliverable power goes up of course (P=UxI, but always keep in mind P=IR^2 as well).

Now, as @pdw also said, the SBrick has overload protection. With trains hauling some load, the motors attached will try to get as much current as possible (as I am familiar with your trains). I believe that there is no reason to use MT3608's to step up to 9V: The power UxI is (ideally) a constant value; otherwise we would violate the 1st and 2nd law of Thermodynamics - and these Gods are very, very conservative. The step-up voltage converter cannot hold the same current (lets say 1A) delivered by the 7.2V LiPos directly, regardless of how much you step-up the voltage.

If I were you, I'd just use the LiPos "as is", feed them to the SBrick and off you go.

When you want higher power, use the approach of @MikeTwo9398 (different batteries, different internal resistance). The SBrick will not burn out, regardless what your power source is. It will simply shut off its outputs. As the PF revceivers/PBricks etc. do as well.

All the best,
Thorsten