BJ29 80a/ 6s ESC... have questions

[champion221elite]

I have a Dynamite 80a/ 6s ESC laying around and I'm thinking about using it for an upcoming project.

Would this ESC function well with a Leopard 3674 motor rated at 1400 kv running on 6s? This motor normally draws 1000 watts and has a peak draw of 1500 watts. I've done the amp draw calculations, and this motor will pull between 45 and 67 amps which is less than the 80 amps this ESC is rated for. I obviously don't want to fry the ESC which is why I'm asking here first. The hull will be a 30" cat and I plan on running a modified X442 prop.

I am not set on the 1400 kv motor, as there is also a 1700 kv option, but I'm trying to keep my RPM's down. This will be for sport running. No racing, and nothing wild.

[BHChieftain]

Note that The BJ/ Impluse 80A esc on the stock 1800kv motor isn't reliable on 6S-- while it is rated at 22.2volts, it is only 80A, and many people burn up this esc. You'd need to run a really small prop to make it work on 6S which defeats the point of running 6S (it is a great ESC for a larger prop on 4S). The amp spikes are usually what kills it-- when the boat jumps a wake and the prop exits and re-enters the water. For folks running the stock motor on these boats I usually recommend they pick up an 180A ESC which would give plenty of headroom for 6S + large prop.

That being said, if you use the 1400kv motor I actually think you'd be ok using this ESC esp. if you stick with the x442. Reason I say this is I use an x442 in combination with a UL1 2030KV motor on a 60A AQ ESC on 4S (for a p-limited hydro), and that works just fine-- your 1400kv motor on 6S will make just about the same RPMs as my config, and the higher voltage is actually easier on the ESC all things being equal... I say give it a go if you stay with 1400-- I really like the Dynamite ESCs as they have a nice feel and are super water resistant (I've had several completely submerged and survive).

If you don't have your batteries already, I really prefer 4S configs made from 2S packs. They are cheaper, and you can combine them nicely and use them on multiple boats (can use 2 of them for 4S1P, 4 of them to make 4S2P, or 3 of them to make 6S1P). So I think 1700kv (or 1800kv) with 4S is a nice combination, and that also would work great with the Dynamite ESC.

Chief

[champion221elite]

Thanks for the detailed response Chief! Its been a few days since I posted my original question and here is what Ive done.

I ended up doing a bunch of calculations and ended up ordering a Leopard 3650 which is dimensionally very similar to the ProBoat motors. Its rated at 1650 kv and will pull 800 to 1300 watts. At 6s, it should draw between 36 and 58 amps using a nominal 22.2 volts. I understand that as voltage drops, the amperage draw actually increases. Allowing for voltage sag down to 3.2 volts per cell/ 19.2 volts overall at 6s, my amp draw will be between 41 and 67 amps. I placed a call to Horizon Hobby and expressed my concerns about the small gauge wires on PB motors and asked about the factory 80a/ 6s esc. I was told it will handle a constant 80A load with bursts of 100A. Using this info, it appears the Leopard 3650/ 1650 kv motor should be safely under that limit... especially with an X442 prop.

I ordered from OSE, and im just waiting for my stuff to arrive. Let me know if my calculations are sound. Also, PB says their 1500 and 1800 kv motors are good for .75 to 1 hp. My calculator is saying the 3650 should work out to 1.07 hp for 800 watts and 1.74 hp at 1300 watts. Despite the slightly smaller size, the 3650 might be a touch faster due to having at least .25 to . 75 greater hp.

Finally, I have an ample supply of lipos. All of which are 3s1p packs. I have two boats and this allows for greater ease of sharing batteries between boats as the need arises.

[champion221elite]

I forgot to mention that I have disconnected the BEC on the 80A/ 6s esc. This should further reduce the strain and heat generated in the esc and avoid releasing its magic white smoke.

[BHChieftain]

Disabling the BEC is a good idea. Your calcs need to allow for a lot of headroom as they don't capture the amp spikes when the prop exits, unloads, then re-enters the water during hops-- that is what usually kills the ESC. If it were me I would have gone for a 1500kv motor (I'm biased for reliability vs. speed), but I bet your 1650kv motor will work out ok-- it is just pushing into the reliability curve harder.

Chief

[champion221elite]

Thanks Chief. I wanted a 1500 kv motor, but the 1650 was the lowest OSE sold in that size.

[champion221elite]

UPDATE: The ice finally left my local pond and I had an opportunity to run my Blackjack 29 with the upgraded Leopard 3650 motor rated at 1650 kv. I was using the stock 80 Amp ESC with a sharpened, balanced and cupped Prather S215 prop.

The boat ran great for the first 2:40 of a timed 4 minute run. Then it happened... the boat quit in the middle of the pond. For a moment, I thought the batteries on my Tx went dead, or it entered a safe mode due to a loss of signal. Just then I saw the smoke start coming out from under the taped canopy. No reason to share pics as we all know what a smoked ESC looks like. The factory 80 A/ 6s ESC fought the good fight, but lost in the end. I have now ordered a Seaking 180 v3 from OSE. BTW, the magic smoke inside those ESC's really stinks!

[BHChieftain]

Sorry to hear it didn't work out. Yet another validation point that 80A and 6S don't really mix very well... it might have worked if you used an x440 prop. Anyway, the 180A esc is a much better choice for 6S and will give you more prop options.

Chief

[Darin Jordan]

I was using the stock 80 Amp ESC with a sharpened, balanced and cupped Prather S215 prop.

Ummmmm.... Yup... the ESC Let go...

Guys... the "6S" claim for these boats is for a FACTORY, unmodified prop, which slips and cavitates and ventilates and doesn't "hook-up" very hard.

If you are going to turn an 1800KV motor at 40,000 RPM (yes, I've been reading with some puzzlement on that other thread), you cannot expect to be able to run the same props you ran at 26,000 RPM. Simply won't work. Loading is NOT linear.

That "cupped" part is likely what did you in... I've beat the HELL out of an IM31 on 6S with the factory power system and have never had an issue with heat or anything else, and that was using the stock 4mm contacts. However, I'm running appropriate props. Either a stock prop, a standard prepped stock prop, or a nicely prepped, Prather 215. I've also had good luck with a rather standard ABC 42x55...

[champion221elite]

I had my suspicions about running the 80 A/ 6S speedo, but made the mistake of convincing myself that it would work. Lesson learned, and hopefully I can save others some $$$ by reading this. While the prop was cupped a bit, I wrongly assumed the amp draw would be roughly equal to a stock prop due to it being thinner and properly balanced.

In hindsight, I should have removed the factory 80A and installed the SK180 before running the Leopard 3650. That would have saved me a great deal of problems and money.

[hydro_pyro]

I've said all along... Setup affects the reliability of the electronics. Prop should be stock, balanced and sharpened. Shaft strut needs to be raised SUPER high with some negative angle, which requires modifying the strut and adjusting the stuffing tube. This will give you LOTS of bottom-end slip to reduce motor loading, it will give you more stern lift for better speed, and reduce bowlift to reduce the chances of blow-over. I run my BJ29 on 6s all the time without any problems.

[champion221elite]

Yep to all of those things Pyro... however, my BJ29 is no longer stock.

The Leopard 3650 motor combined with the cupped prop were just too much for the stock esc. I have done the dialed in strut mod, which helped with the hull bouncing.

In hindsight, I should have removed and sold the 80 amp stock esc and gotten the SK180 from the start.