Caution - Hifei capacitor board installation

[Old School]

For some reason Hifei capacitor boards have cutouts each side that would take an automobile battery lead when a cutout much smaller would make battery connections much easier and avoid the pitfall that I have fallen into. I am using gauge 8 wire from my batteries to the Hifei capacitor board and then to the 8mm bullet connectors on the ESC connection. My boat has two 4s batteries in series each side, then paralleled to the ESC connection. This afternoon I soldered the Hifei capacitor board each side, inline with the battery supply to the ESC connection. I connected everything up and everything worked fine. Leaving the four batteries insitu and connected to each other in series, I disconnected the two positive leads from the ESC connection and securely stowed them. As I had an important phone call to make I rested the hatch back on the boat. Approximately 45 minutes later I could smell a burning odour. When I lifted the hatch a cloud of smoke emerged, with a thin layer of black soot over everything. The right hand capacitor board was totally destroyed. The heat totally melted the ESC on/off switch as well as cosmetic damage to the battery supply leads.

I must presume that the factory test the capacitor boards prior release so can assume that in soldering my gauge 8 wires to the capacitor board that excess solder has shorted out the capacitors on the board. I am very experienced at soldering so this is not down to carelessness or lack of ability on my behalf. I believe the capacitors are rated at 63 volts so my 32 volt supply should not have caused the capacitors to self destruct. I will source another capacitor board but in hindsight, view these boards as liable to be a source of future problems. I could have totally destroyed a very, very expensive boat even before it sees a drop of water. I am hoping that the ESC has not suffered any internal damage. I did a cell check of the two batteries on that side and all cells were fine. I believe that the battery supply wires will be OK but as the ESC switch is destroyed along with the attached wires almost back to the ESC case then I may possibly delete the switch.

I am not impressed as I see the design of the Hifei capacitor board as a very poor design, as the cutouts where the battery wires are soldered to are far too large and in reality should be sized to be a snug fit. I now have a very messy cleanup job to complete. I am thinking that when I solder in the new capacitor board I will use thin offcuts of brass tubing soldered to the battery leads to increase the diameter of the gauge 8 wires to match the oversize cutout diameter on the board.

[Old School]

This is what happens when the smoke gets out.

[plinse]

Thank you for the Warning.

What I don't really get is the reason for the delay. When I look at the wreck of the capacitor board the Caps still look pretty ok, the cans are still closed and it looks like the board itself burned for some reason. What I ask myself is the reason for the delay of the short circuit that was caused somehow.

The other topic: The capacitors should be placed as close to the ESC as possible - not batterie side, they definately belong to the ESC-side of the connectors.
Did you do that?
Propably not but if you had done so the power would have been cut with the "ESC +" being disconnected.

Actually this makes some differences in electrical behaviour and the effectiveness of the board but it makes no difference according to the board not being supposed to catch fire...

Best Regards, Eike

[Old School]

I have provided a link relating to capacitors and their placement. I have only read the first page, but while the common opinion is that a capacitor board should be as close as possible to the ESC, apparently this is not so much to do with the length of the wires but limiting the number of connectors between the capacitor board and the ESC. In my case the capacitor boards were placed where they could be conveniently fitted, being less than 6 inches from the 8mm bullet connectors that then connect to the ESC with wires less than 3 inches in length. The wires are gauge 8. The left side capacitor board was soldered and connected in exactly the same manner as the capacitor board which destroyed itself.

https://forums.offshoreelectrics.com...all+capacitors


Consider that the board destroyed itself not while under load as the positive wire had been disconnected from the circuit to the ESC so any current draw was most likely a short circuit through the capacitor board. Also the batteries showed no sign of power loss as a check of all cells showed them to still be at their charged state.

[Peter A]

In your other build thread you said you were mounting the cap boards on c/f plates. Did you insulate them from the plates?

[plinse]

To me it looks a little like the layers in the multi-layer board were not properly seperated and got contact somehow
As mentioned before the Caps itself look fine, if they would have had an issue they would have burned immediately and look different now.

The RC-Guy opinions on placing cap-banks are nice but as an electrical engineer I skip the thinking and smalltalk

The battery is a big but slow capacitance and you have the impedance of wire and connectors between the batterie and the ESC.
You want to minimize the resulting voltage-ripple from its switching at the ESC. The closer the Caps are located at the ESC the more effective they are. If they are "behind connectors" you can't compensate the ripple from sending switched current through the wires and connectors that are between ESC and cap bank.

Whether you need additional caps is a topic on it's own.
The ESC has caps on it and if they were dimensioned right you would not need any additional
Reality shows that cap banks help, I use them myself but I solder them myself.

I am not willing to pay 13$ for 4 caps worth 1,50$ and then some producers don't get such a simple board which results in a boat filled with a carcinogenic layer of burned plastic/epoxy/...
And you already mentioned the terminals not fitting reasonable wire as well.
During the time you are adapting that I have my cap bank finished and they never failed so far

In your other build thread you said you were mounting the cap boards on c/f plates. Did you insulate them from the plates?

He hopefully did - otherwise we have a good indication for a possible root cause

Best Regards, Eike

[Old School]

Thankyou all. There was a layer of 2mm G10 fibreglass plate separating the capacitor board from the mount. Even so, I would have thought that the capacitor circuit board would have been insulated around the edges as the board itself is an insulator and as the board was positioned the battery lead connectors would have been at least 1 cm away from any carbon fibre.

Edit: as regards additional caps, the Hifei Swordfish Pro 300 amp ESC has a sealed aluminium case with no external caps visible. One would assume that the design would incorporate sufficient caps internally.

[plinse]

Thankyou all. There was a layer of 2mm G10 fibreglass plate separating the capacitor board from the mount.

That would be ok.

Even so, I would have thought that the capacitor circuit board would have been insulated around the edges as the board itself is an insulator ...

The epoxy plate is the carrier and the insulater but they are copper plated. I would at least expect copper on both sides, + on one side, - on the other with some shaping of the plane so the soldering terminals would be both sides with some interlayer connection.
The shape of the copper planes is usually formed by acid etching, the mechanical shape of the board by CNC cutting/CNC milling. Commercially produced boards then are usually coated with some varnish but leaving the terminals for soldering bare metal.

If there was not enough copper removed from the outer contour or the CNC milling came too close to the copper you can have copper burrs in the edges from CNC milling. Varnish does not cover burrs securely.
Yes, the simple thinking would be that such a board is "ready to use" but I would always insulate such a board once it is soldered to the power wires with heat shrink.
Check the other board and the new one for signs of what I have described. You can't tell based on the burned one any more but this is what I would be looking for having seen the damage. There was something that was supposed to be insulated and the insulation was good enough for some first testing but it had failures that generated the bigger failure.

Edit: as regards additional caps, the Hifei Swordfish Pro 300 amp ESC has a sealed aluminium case with no external caps visible. One would assume that the design would incorporate sufficient caps internally.

True, this is what I mentioned here:

...
Whether you need additional caps is a topic on it's own.
The ESC has caps on it and if they were dimensioned right you would not need any additional
Reality shows that cap banks help, I use them myself but I solder them myself.
...

Sometimes the caps are dimensioned ok, sometimes not and I also made the experience that some manufacturer change their mind.
It is many years ago that I ran a Plettenberg/Schulze Hotliner-Drive. It was the former state of the art for F5B and after 2 seasons my controller suddenly failed. I send it in for repair and Mr Schulze called me saying my connecters would be crap, they speeded up the failure. He could repair it and he would double up the capacitors and if I wanted to be on the safe side I should exchange the capacitors after a season or two - and I would have to exchange my connectors (new ones and a better type).

Capacitors are a lifetime-Issue.
They are pretty easy to dimension when it is close to the nominal lifetime, Rubycon ZLH-Type are often named to do 10000h but this is correlating with limited ripple currents and nominal temperatures. Increasing temperature and ripple current both decrease lifetime with at least second power of changed value. When you think of the F5B drive I have mentioned before and that the caps were ok for a season or two... then we are down from 10000h operation to perhaps one or two hours of operation as the motor runtime you really get out of the batteries is pretty low
This is pretty far away from being able to calculate it well.

F5B drives are really pushed to the limits but lets call it 5-10h on a standard Brushless ESC as estimated lifetime. This is 0,1% of the designed lifetime of the caps. It is brutal abuse if you ask Rubycon or Panasonic
Most RC-Guys will not exceed a few hours and the ones who do so usually run on lower load and more runtime which helps the caps.

The reason why I add Caps is that they are much easier to replace then the ones inside the ESC.

This is also why I love the Seaking 180 V2 as also the caps of the ESC are easy to replace and I hate the ESC where the caps are glued in. They really are one-way-products. You can only expand the lifetime by adding external cap banks but then you should definitely minimize the distance of the bank to the ESC and have NO connectors in between.

Regards, Eike

[Old School]

Eike,
many thanks for the detailed response. As there was no external circuit with the positive lead disconnected at the ESC then there must have been a short circuit across the capacitor board that formed the circuit leading to the destruction.