LYEN 18FET Max Amps?

(Lifted from my other Thread)
I upgraded to more capable batteries - 14S Lipo / I have a 18FET Lyen from years ago...



Question:

I have a LYEN MK2 18 Fet - how many amps can i push trough before the magic smoke escapes?
Lyen just told me back in the day:

The recommended maximum output for the 12 FET 4110 controller is around 3500 watts and the 18 FET controller is around 5250 watts. Power=V/I. So let say you are going to run 22S lipo at 81.4v nominal voltage. You then divide 3500 watts by 81.4v and you get around 43A for the 12 FET, 5250/81.4=64.5A for the 18 FET. Or for 24S is 3500w/88.8v=39.4A for the 12FET and 5250/88.8v=59A for the 18 FET.

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At 14S Lipo that would equate to ~100A. Good idea? :| Anyone got Experiences? Thanks.

crossposted from your other thread:


I don't have a direct answer for you, but some points to consider:

The FETs themselves have a current limit, usually in the leads to the FETs from the board, and the interior leads to the die from those external leads. This equates to a phase current limit which is higher than the battery current, because of the way the controllers work...but these controllers cannot sense the actual current in the FETs, and just calculate it based on internal settings (battery/phase ratio) and the battery current limit (assuming no shunt mods, which disable the ability of the controller to know what the current actually is, and thus unable to protect itself).

You can look up these lead and die limits in the spec sheet for the FET used, and there is likely discussion in old modding threads (especiallly by Methods, Fechter, Liveforphysics, and others around a decade ago when these were the best you could typically get or hotrod) concerning these limits. Most of them will be about "infineon" controllers.

Then there is the ability of the FETs to dissipate the heat generated in them, thru the multiple layers of thermal barriers between the die and the air outside the case, and then the airflow over the case's ability to carry away the heat that does finally get out of the case.

Then there is the wire thickness, both phase and battery, vs the amount of airflow over the wires, vs the time you'll be using that much current.

Oh, and this discusses the fet heating issues
https://endless-sphere.com/forums/viewtopic.php?p=1565550#p1565550

The max amp (battery and phase) current settings for any given controller are highly variable depending on motor, load, terrain, type of riding, and placement on the bike in terms of air flow.

The one I had years back was modified by LYEN to run 75 amps......at 20s. I’d say that is getting close to your limit as them max you should run.

Tom

As the others have said, it really depends on the motor, how it's being used, and a bunch of other things, like does it have the buss bar mod, does it get good airflow, are you laboring it at part throttle, or at full throttle..

I used an Lyen 18 FET on my Monster bike. I slowly upped the power over the course of a couple years, with tweaks to the programing and the build to optimize it for peak power. I finally pushed it to 200 battery amps on a 24s battery pack, and then blew it up within a few months.

So I could tell you it's capable of 200 amps, but you might blow it up at 40 amps, depending on your motor and usage.

Thanks for the replies

Edward Lyen also responded via mail:

100A is around 5180
watts which is near the maximum power value. Therefore, you would need
to be very careful to monitor the temperature closely to avoid it
overheating. Be aware it will put a lot of stress on the motor,
controller, and battery.

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The max amp (battery and phase) current settings for any given controller are highly variable depending on motor, load, terrain, type of riding, and placement on the bike in terms of air flow.

Click to expand...

of course. The controller has good airflow and i mounted an additional heatsink.
i'll just run 75A for a while and slowly increase it to 100... in hopes it doesn't pop haha

Drunkskunk said:

As the others have said, it really depends on the motor, how it's being used, and a bunch of other things, like does it have the buss bar mod, does it get good airflow, are you laboring it at part throttle, or at full throttle..

I used an Lyen 18 FET on my Monster bike. I slowly upped the power over the course of a couple years, with tweaks to the programing and the build to optimize it for peak power. I finally pushed it to 200 battery amps on a 24s battery pack, and then blew it up within a few months.

So I could tell you it's capable of 200 amps, but you might blow it up at 40 amps, depending on your motor and usage.

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well, it didn't blow on 60A (what i rode the last few years)

what controller did you use after you fried your lyen?

Wummi said:

The controller has good airflow and i mounted an additional heatsink.

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If the heatsink is just bolted to the existing one, it's nto nearly as effective as if you replaced the existing one with a better one (better can mean a number of things dependign on what you need it to do, continuous heat dissipation or burst of heat absorption and reradiation).

The main problem is getting the heat directly out of all the FETs at teh same time equally, so that their resistance remains similar and current is shared better, so you don't end up with one that ends up with more current than it can handle and pops, causing a chain reaction.

But as long as it works...it's probably better than nothng.

amberwolf said:

Wummi said:

The controller has good airflow and i mounted an additional heatsink.

Click to expand...

If the heatsink is just bolted to the existing one, it's nto nearly as effective as if you replaced the existing one with a better one (better can mean a number of things dependign on what you need it to do, continuous heat dissipation or burst of heat absorption and reradiation).

The main problem is getting the heat directly out of all the FETs at teh same time equally, so that their resistance remains similar and current is shared better, so you don't end up with one that ends up with more current than it can handle and pops, causing a chain reaction.

But as long as it works...it's probably better than nothng.

Click to expand...

True, but changing the existing heatsink solution would mean a case redesign. ain't nobody got time fo that!

if i pop the FETs, i might think about it