MMM UBEC option
 

Until the whole BEC issue with the MMM is sorted out, I decided to mod my MMM to use an external UBEC. But the wiring was a little messy. So, I took the mod a little further.

1: Carefully remove the red and black wire from the MMM PCB.

2: Solder the UBEC inputs directly onto the + and - contacts of the MMM

3: Insert the throttle wire from the ESC into the empty slot on the UBEC output connector.

What is left is a fairly compact package that looks fairly clean. A couple pictures for illustration:

http://scriptasylum.com/forumpics/mmm_bec1.jpg

http://scriptasylum.com/forumpics/mmm_bec2.jpg

Hope it helps someone...

Important Note: To program the ESC via the Castle Link, you have to treat this mod as an Opto-isolated ESC. This means you need to connect a set of batteries to the ESC. Normally, the Link cable powers the needed ESC circuits for programming, but when the BEC is disabled like this mod, the ESC cannot get 6v power from the link to the ESC.

Also, the red wire at the end of the throttle cable needs to be temporarily removed while programming. Failure to do so causes the UBEC 6v output to "fight" the Castle Link 6v output. Either temporarily remove the red wire, or use a servo extension with the red wire removed (this is what I did).

Oh, and don't forget to turn the ESC switch on. :smile:

you run your esc without a fan?????and if my esc fail i cannot do this mod???

Looks nice and I like the heavy duty switch you added. I think that is a necessity as the plastic switches wear out quickly in my experience. Looks like the koolflight bec? I know it's not programmable like the CC bec but it sure does work well and I guess I don't see much of a need for programming anyway. The CC bec has me concerned due to any failure releasing full voltage.

Yes, I'll be running the ESC without the fan (hence my avatar). And yes, that will void the warranty. If you want to use the fan, you can simply plug one into the Rx since that will be powered via UBEC. As long as you use a fan, CC should honor the warranty. Don't know if they'll accept this mod though...

Yeah, I've heard a few bad things about the switch, so I replaced that too. Yup, it's a KF UBEC. They work well, and provide a real 6v output, even under load. Knowing how the CC BEC sends full battery voltage if it goes bad makes me not want to use it.

Note; even though I'm using the UBEC, the internal one is still functional but only powers the internal circuits. If using the stock fan, I would re-wire it to the Rx to prevent the possibility of blowing the internal BEC. I would rather replace a blown external UBEC than the whole ESC...

Very very neat setup for those that want 6v...

Just a thought does the internal BEC have its own ground?

Just wondering if you shouldn't have routed the ground from the old ESC line to the battery gound...

Photos aren't working for me

Brian's Web server is down...

The ESC power and BEC grounds are common. A continuity check confirmed this (in both directions to rule out any diode isolation). The UBEC ground is common between input and output as well.

This wasn't primarily done to get 6v, but to remove any external loading from the internal BEC. I figure if the internal BEC just takes care of it's own circuits, it should be fine. Most (if not all) failures I've seen in the other thread are when the internal BEC is used. I haven't seen a setup using an external BEC fail yet. The 6v output is just a bonus. :smile:

Yeah, my server is down. I forgot to pay the bill. :oops: The old CC on file didn't work - I lost my wallet a while back, got a new CC, but forgot to enter that info. Just paid the bill, but may take a little while for it to go through...

Sweet mod. I have not done any mods to my MMM and it is running fine. I run 5s with a 1y in a Savage and i hit jumps (hard too) and the MMM is still working fine (knock on wood). I dont know why mine still runs fine?? Everyone i know on the boards their MMM has failed. Hopefully mine will stay running good. I am debating on doing this to keep it running though. but since it has been running so good for so long should i mess with it. besides i would rather just utilize my warranty if it does eventually fry.

I thought the same thing. I had a MMM with a good 20-25 hours of hard racing on it and it just died last weekend. I thought I was going to have one of the few that actually survived. It ran great for months now (aside from the fan issues) and through all 3 qualifiers for the day and then when I went to plug in the battery and turn it on 5 minutes before the main.... nothing. Dead.

I have 2 other MMMs. One with maybe 4-5 hours on it and the other with only an hour or so. They are both still running, but as soon as CC gets this thing back into production I will be sending them in for replacement with the new version, faild or not.

my thoughts exactly. I will send mine in for a new version too (regardless if mine still works or not)

I got about 15 Hrs on mine before it failed...but now we are in the monsoon season in Az so it doesnt matter its too wet to run anyways.....:-(

You do know that ALL switching BECs have the same issue -- if the output FET fails, it sends full voltage to the output.

It's inherent in the design of a step down (buck) dc-dc converter.

Patrick

That is true, but for some reason, the others have some circuit integrated into the IC to help prevent that (or at least reduce the chances). Usually, when they go, they just stop working.

Hmmm, not that I know of. I've seen many many UBECs die myself, and put full voltage out.

Any BEC that uses an external FET (pretty much anything over 2 amps) has the same possibility for full voltage output type failure as the Castle BEC.