[Dr_C2]

There has been reference on this forum and slotforum of a new version of the C7005 retrofit SSD decoder. The new version can be identified by the white marking “11/2022”. It can also be identified by the absence of the silver cylindrical component (a 100uF electrolytic capacitor). The latter makes this a very compact retrofit SSD decoder solution.

The photo shows the top side of the decoder - including a decoder with a JST ZH 1.5mm pitch lighting socket fitted.

     

Key technical details:
=============

1/ Microcontroller:
16F1503 (same as C8515 rev H)

2/ Motor MOSFET:
DMN3404L
Marking “34N”
Max current* =5.8A at Vgs=10V
and 5.2A at Vg=ls=4.5V

3/ Brake MOSFET:
DMP3098L
Marking “DMB”
Max current* = -3.8A at Vgs=-10V

* when operating at 25 degrees C

4/ Four Schottky diodes as full bridge rectifier.
Labelled “SS34”
Each has a 3A max current limit giving a total capability of 6A for SSD AC drive packets.

5/ 100uF electrolytic capacitor replaced with six parallel wired MLCC (very low profile)

6/ head and tail lighting circuits which are npn transistor buffered.

Assessment:
=======

The C7005 rev 22/2022 has a similar footprint to the older C7005 and has a significantly reduced thickness profile due to the elimination of the electrolytic capacitor.

The new C7005 has a motor/brake current limit of circa 5A/3A (i.e. very similar to the C8515 rev H) so should be compatible with higher torque motors. It also has lighting circuits as per the C8515 rev H and so represents an excellent retrofit decoder for both F1 (due to its small dimensions) and saloon/GT cars (due to the lighting circuits).

Overall, an excellent upgrade to the C7005.

[Dr_C2]

I traced out the motor/brake drive circuits for both the C8515 rev H and the above new C7005 (ver 11/2022). Both have identical topology (i.e. same schematic) and both have the same motor drive transistor (DMN3404L).

Both, therefore, will have very similar motor drive capabilities - with just one minor difference due to the differences of layout and size of the PCBs. For SOT23 packaged devices (i.e. the three pin package used for the DMN3404L) the maximum safe operating current is a function of the heat sinking properties of the PCB including its layout and size. That said the difference should be quite small in this case.

Allowing for a small safety margin a sensible limit for motor current is 4A for both the C8515 rev H and the C7005 ver 11/2022.

For cars running on a track both decoders should be fine even for higher torque motors such as the NSR King 21 EVO (350g-cm) at 12V. But note the stall current at 12V is 8A so in the scenario of a full power stall the MOSFET will fail before the motor windings become damaged.

For medium torque motors such as the Slot.it V12/4 23k (170g.cm) the same of course applies for cars running on the track at 12V i.e. they should drive OK. For this motor the stall current at 12V is 3.5A so typically the decoder will remain undamaged even for a sustained motor stall. However, in this stall scenario damage to the motor will result - it will be dissipating 42W.

I guess folk will have different views on which it is preferable to replace… a motor or a MOSFET?

Of course the real answer to the question is to avoid motor stalls :)

i.e.

- keep the track clear of foreign objects which could get trapped inside and jam the motor.
- avoid holding the wheels locked when powered up
- avoid snow ploughing through crash sites
- avoid using motors which are damaged and draw excess current

With these precautions both the C8515 rev H and the new C7005 should be fine with medium torque motors (e.g. V12/4) and higher torque motors (e.g. King 21 Evo).

I don’t plan to test either of these decoders or motors to destruction (I’ll leave that to others), but I will run cars with both types of decoder and with both types of motor and report back.

c