Thundercat 31 conversion build

[txboatpilot]

I have 2x 4000mah 20C's and 2x 4000mah 25C's. Can I serie a 20C and a 25C together and then parallel two sets to the ESC? That would theoretically produce 180A MAX. Would the Etti 150A be able to handle it?

Or should I just stick to the 25C packs (100A) and forget about the 20C packs?

I now understand the theory behind ripple current and why high volts and low amps don't mix...

You could run those pack together, but it is recommended that they are the same C rating..

The Etti is fine, next time add the cap board for extra protection... I would go with 4x 3S 4000 25C,,, if you can...

The High Voltage and Low Amps is correct and does mix or work very well,,, only when you have the right batteries to back it all up!

[calcagno45]

Its better to be able supply more than enough Amps, than not enough. 2P setups are recommended especially when pushing this hard.

[lomdel]

The 13XL is not ok Its ceased... Expensive mistake

[txboatpilot]

The 13XL is not ok Its ceased... Expensive mistake

Sorry too hear about the motor!

What does your boat weigh RTR?

[DISAR]

Big mess. I am really sorry about your situation. But this is a very weird case. The ETTI most people say is super durable. The feigaos are also good, so what went wrong? According to the FE calc. your setup had max. 80 amps so it is not a matter of high amps I guess. For the ripple current I don't know, can it also destroy the motor? Let me also ask you some questions to see what's happening

a) As above what is your boat's weight RTR
b) Where is your COG
c) Where is the bottom of the strut comparing to sponsons bottom
d) Maybe some cables on the motor had the heat shrink off and had a short circuit?
e) Maybe the bolts holding the motor were touching or almost touching the motor windings?
f) The shaft was rotating freely by hand or sticking somewhere?
g) How long you were playnig when this happened
h) Did you change any seetings on the ETTI apart from the 6s lipos cutoff?
i) According to the Fe calc your setup is max. 80 amps but your watts are 1500, quite high for a Feigao especially when running for over 3 mins. Maybe the motor burnt first and then the ETTI?

It sounds like policeman investigation but we have to find out what went wrong, otherwise it may happen again.

[lomdel]

Thanks for your interest! I hope the below answers help.

a) As above what is your boat's weight RTR.

I stripped her completely yesterday trying to clean up the mess the blown electrical components made, so I can't weigh her right now, but she was by no means a heavyweight...

b) Where is your COG.

My COG was exactly 32% from the transom/sponsons

c) Where is the bottom of the strut comparing to sponsons bottom.

The bottom of the struts was set at its highest, approx 15mm from sponsons bottom

d) Maybe some cables on the motor had the heat shrink off and had a short circuit?.

Nope. All heat shrink wraps in order.

e) Maybe the bolts holding the motor were touching or almost touching the motor windings?.

I have two clamp down mounts that you can see if you scroll back in this thread. I made sure that they were not tightened too much to exert some pressure.

f) The shaft was rotating freely by hand or sticking somewhere?.

Rotated freely

g) How long you were playnig when this happened.

It happened after about 3 minutes

h) Did you change any seetings on the ETTI apart from the 6s lipos cutoff?.

No. It so damn confusing the beeps, bleeps and rings anyway...

i) According to the Fe calc your setup is max. 80 amps but your watts are 1500, quite high for a Feigao especially when running for over 3 mins. Maybe the motor burnt first and then the ETTI?.

I think that one of the motor bearings might have been damaged, because I found a few bearing balls rolling around in the hull afterwards, and the rotor won't turn by hand anymore. That and the fact that the 80A lipos couldn't deliver what the Etti was asking, was probably the cause. I also think the prop S220 was a bit big, should have stuck to the S215.
I'll never use those 4000mah 20C lipos again. Luckily I have some 25C's as well that I acheived 45mph with.

In the end, what would you guys suggest for a proper 45mph+ set-up in a 31" cat, starting from scratch, but stick to Feigao motors...?

[DISAR]

I think that you were unlucky. The damaged ball bearing maybe due to defective material? Maybe this caused the damage? I don't know.

Well I will tell you what feigao setup I had on a 36" mono, certainly heavier than yours, but run it only 4 times. I was afraid not to damage the motor because it is small for this hull.

Feigao 9XL
4s1p (2 2s bats 4900mah, 25c, polyquest and elite)
prop 445-646, greatest speed 60 klm/hr (40 mph)
Max 80-90 amps

For your boat I would suggest 6s2p, 10xl,442 or s215. Always run 2p from now on to avoid problems. Again with this setup the 10xl is at its limits. If you 11 xl put that one first. However, to achieve the speeds that you want safely you need a feigao 580L motor around 1500 kv.

[DISAR]

A 580 8L, 6s2p, 442,445,s220, etti 150a will be perfect IMO

[lomdel]

Only problem there is mounting the 580's larger can to reach the flex-shaft ...?
What about the HXT 120 or the Turnigy 100HV ESC's?

[DISAR]

With the 10 or 11XL I believe you will have 80-100 amps if you want to run 6s. Have you thought running first 4s or 5s which is safer?
The HXT 120 might work, the turnigy I don't know and. The HM200a (http://www.himodel.com/electric/HiMo...200A-OPTO.html) or the mystery 200a will work, but you have to watercool and waterproof.
I had used a 100a Esc with the feigao but there is a point where it will overheat and stop. After it is cooled down a little bit start again.

[lomdel]

I don't have 4S or 5S packs. This build is costing me way more than expected already, so I can't buy more lipos.
Any source or tips on waterproofing these ESC's (conformal coating) and attaching the cooling plate (thermal paste)?
I will try to repair the 13XL with a new rotor and bearings, otherwise I will use the 11XL as soon as that arrive. Still no ESC however...
I will also try to serie my 2x 4000mah 20C and 2x 4000mah 25C packs and then parallel them to the ESC so that it can receive max 180A. (?)
The S215 will go back on for now.

[lomdel]

Just ordered the Himodel 200A ESC! $85,00 including shipping is a steal, should have ordered two. I will use the DP270 method of waterproofing and watercool by grinding the heatsink to insert 4x brass tubes as mentioned and shown in a previous topic. Cheap enough just to get me in the water again, maybe later will opt for another Etti or a CC 240.

[DISAR]

Good. Just an advice do not use the DP270. Please read this
http://forums.offshoreelectrics.com/...ead.php?t=6213
and this
http://forums.offshoreelectrics.com/...ead.php?t=6177

What I did with mine is insert two 5/32 tubes in the fins and then placed on the fets, on the other side used a custom made cooling plate with two tubes. The cooling plates are attached on the boards using the thermal grease silicon compound (you can find many in e-bay, or here or your local electronics shop).
Then I use heat shrink and wrap all the esc and cooling plates together. And finally use normal silicone to seal the two ends.

[lomdel]

What's your opinion on the usage of Corrosion-X for waterproofing?

[lomdel]

I found the reason why the 13XL ceased! I took the rotor out and found that 2 of the three magnets cracked and pieces came loose and digged into the windings, damaging them beyond repair... See pics attached.
Steven, what's your policy regarding faulty magnets splintering off your Feigao's? Any return and replacement option? If you read posts above, you'll see what set-up (6S) I ran that day.