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headhunter23

Need a little relay or transistor help

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Ok, not for planes or video(which is why I stuck it in floopydust), but using the pic switch project from rc-cam. Ok here's my dilema, just finished a little beauty rc jet drive boat. Fortunately the esc has reverse. Problem is on 11.1v amps go above and beyond esc (pulls 64 on 50 amp esc). Rather than risk the esc, am going to replace it(with 100amp in case I want to crank voltage up further to 84). But unfortunately there are no other esc's that have reverse in this amp range (yes I can do with out it but for running streams and such, it's handy, specially being on a rock).

So my question is... what's the best way to tackle this?

I've been thinking of making a little chip that switches two of the brushless wires, so I can get forward and reverse. But I would like to make this as light as possible. I know a little about relays but something that can handle 60amps going though it to me seems large. Not sure if there's a way to do it with transistors, would probably require a few if I go that way, correct? If someone can just point me in the best direction, it would be appreciated. ;)

Ivan.

Edited by headhunter23

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Can't tell you how to do it, but, forget the transistors and look at Mosfets. The same animals as used in ESCs.

Edited by W3FJW-Ron

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Is it possable to hack the controller to do this using the original FETs ?

Depends on the controller I guess. Also you will need to be able to stop the motor before going into reverse or it may get a bit nasty.

Terry

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yea wondered about the going from forward to back... hmmmmmmmmmmmm.................. nuts. hmmmmmmmm............I don't have enough skillz to hack the board. Plus don't have board yet, need to order it this fri when more funds are available. Perhaps would have to wait on hacking board till it comes in then.

Still just kinda curious at this point, as to what it would take to have a separate board that could be plugged in between esc and motor. Obviously would need a safety so it wouldn't switch the wires till motor has stopped. See there aren't a lot of you geniuses in the rc boating world, or atleast nothing like this board. And I know there are a lot of people that would like reverse on their boats but are stuck using the airplane esc's although some esc's are now having reverse. But those esc's are limited to 25-50amps, although I saw one 60 amp the other day, but still it would be nice to keep the esc you already have and just add a chip to get reverse. Would this be a relatively simple project?

Edited by headhunter23

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Would this be a relatively simple project?

On a brushless controller, this is a firmware (software) thing. There have been some published firmware hacks for ESC's. For example, the MikroKopter project has involved several published firmware hacks. But I don't know of any that were created to add reverse, but for inverted MK flight it would come in handy :) .

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Not really. Knowing that in order to work it would have to receive the control pulses from the receiver, and control the "real" ESC itself (make it start only when it knows it's OK to do it), and integrate a power stage, it would take like 80% of the design of an ESC altogether...

A more realistic way would maybe be to take your current ESC, and replace its power FETs with more beefy ones that can take more current.

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ahhh so that's what ron meant by fet's. See now that's doable.... question, I'm assuming bigger mosfets won't fit where the current ones are though, correct?

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You may be able to piggy back the same size FETs onto the existing ones to double the current handling ability, however this will not increase voltage handling capability. You'll have to use a different FET within the same or a different family to accomplish that.

Edited by W3FJW-Ron

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:) See I love this forum, go in with one idea, come out with better way to do it. I don't need more voltage, just amps. Any tips on where to get fets, I'm assuming I need the code off one of the current chips(which is encoded in goop).

Ivan.

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First thing to do is try to get a number off the fets and google it. You may luck out. My average on identifying stuff like this is about 50%. If google can't get it then then try a search on Digikey, Allied Electronics, and other large suppliers. If your ESC has a name or number or both on it try searching on that. With luck you may wind up with an instruction manual or other data from the mfgrs site that may offer a clue.

One thing to keep in mind is that many ESCs are identical and come from the same mfgr but with different brand names & numbers.

Edited by W3FJW-Ron

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One thing to keep in mind is that many ESCs are identical and come from the same mfgr but with different brand names & numbers.

Gotta love branding. Will take a look see what's what. Thanks all for help. :)

Ivan.

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Btw thought of this last night. If I double the fets, or piggy back them with the same chips. I would reach my goal of 100amps. But, can the fets underneath still be cooled? I do up some alumium, slap some holes in it and add water cooling. I can cool the top layer for sure but not so sure the layer underneath would get any of the cooling benefits. Should I get some cpu tape and put that between the fets? Or any other ideas of cooling? (I'm hoping piggy backing is indeed just soldiering another fet on top of the current ones)

Ivan.

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You are right to think cooling is important but by fitting double the FETs you will half the resistance so only half as much heat will need to be shed. As the cooling of the second set of FETs (or the first) will have less cooling the total power will not be double but a bit less.

If you add very good (water) cooling to a 50A controller then it will probably handle 100A with no problem. Most of the FETs used can handle many times the current they do in speed controllers but have very poor cooling due to size and weight requirments.

Terry

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If you add very good (water) cooling to a 50A controller then it will probably handle 100A with no problem.

The FETs yes, but I'd still disassemble the ESC and check the PCB traces and all other things in the path and reinforce if needed - those might well have been designed with the rated current in mind.

I'd start by taking the controller apart (you'll need to access the solder pads to solder new FETs anyway) and firstly looking at the part numbers on the FETs, then starting to find their characteristics and equivalent parts, then thinking about how to arrange them for cooling. Keep in mind that they need to be electrically isolated from each other! If you do some piggyback then the 2 you paralleled can of course touch each other, but the different legs of the bridge must be isolated.

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Mmmm... good to know on the fets, thanks for your input terry. Kilrah, ya went a little above my head with analyzin the board, don't have that much skillz yet. Which things would I need to look at specifically to reinforce? Like the two capacitors?

Edited by headhunter23

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Kilrah was talking about the copper tracks that connect to the FETs, they must be up to the job. It depends just how much harder you want to push the controller, just bare in mind you may need to solder on some thick copper wire to connect to the FETs. You may not need to on all controllers though as some are very beefy.

Terry

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Will carefully start pulling the goop off the esc tonight, will get photos and numbers then. Perhaps u guys can take a gander and lemme know what's what. I'm not going to push too many amps through it, 64 is what I need, but I know it can pull 87 amps on 14.8v(which I might do a couple times), which is why I figured it was safer to get 100a. These are burst numbers, unsure what the constant running is for the esc in the boat, would need to record wattmeter with camera while running. I don't have a data logger, if anyone asks. :(

Ivan.

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