I don’t see any pitting on the contacts caused by arcing, at least not on one side (the other side is covered in melted plastic). This leads me to believe that my connection worked loose after all those flights. A loose connection would cause the one stud to get hot and melt the plastic. So now I’m debating if I want to bother with a precharge or even parallel switches.
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Is anyone familiar with the Exomo electric paramotor and what they use for a battery disconnect switch and pre-charge system?
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It turns out my switch does have evidence of arcing so I designed a precharge switch:
Hi
You ever get around to testing these?
Cheers
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You will never get an arc with the switch off. To take advantage of the antispark connectors you would need to turn the switch on before connecting them.
I was wanting the larger connectors for the 8ga wire I used.
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I ordered them anyway - one for better current handling and 2 for the size, I f’ing hate pulling smaller connectors apart. The 60’s are a b!tch to get fingers on for pulling apart so just take it to the next level past the 90’s to the OSE’s.
I am also toying with seeing if I can upgrade all my batts to #8 or maybe #6 wire and these connectors.
I have not read this full thread but I know from building our VeFoil (flying jet surfboard) that standard RC (remote control) wire sizing just does not cut it for safety. There is a huge difference in running something remote controlled without your being attached to it VS something you are strapped to thousands of fee up in the air.
I had to meed Canadian and US Coastguard wiring regulations and this will be an eye-opener for most of you still thinking 10awg, and even 8awg are heavy duty.
I am not trying to be negative here just want to make you think twice about your wiring. 400+ degrees wires that are desoldering, and or a flare up on a lipo if your body gets exposed to those while flying gives you two options… both do not end well. I cannot stress enough the importance of certified low awg wire, and heavy duty connectors likely WAY heavier than you are using now. An extra day worth of upgrading and a $100 more in parts is no brainer.
Also, see this post on Li-Ion battery with on/off switch built in: Power cut off switch - #2 by VeConcepts
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100% agree.
People are getting away with small wire because they are not flying full throttle for extended periods. But it’s real sketchy. As you say, even 8 awg doesn’t satisfy current demands.
I do worry about someone doing full throttle climb for more than a breif time.
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Yup. 8awg you can run 200A bursts for a minute or so, but beyond that its getting and Dangerous, I just don’t see the reason for it when you can buy 6 or 4awg for $50 and do it right.
I value my life and safety, its only going to take one near miss from each user and they will upgrade their wiring and connectors, some need to learn the hard way, which I do all the time, but I’m on the ground when it happens 
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How hot is too hot? The ESC’s only have 12awg wires on them. I spliced 10awg wires into them. Perhaps I should have cut the 12awg wires shorter and moved the splice closer to the ESC. I’ve pulled 80 to 90 amps through them for several minutes at a time. I often feel around for heat immediately after landing and have never felt even the slightest heat coming from them. Perhaps the airflow is cooling them as all of the small wires along with the ESCs are out on the arms.
How hot is too hot will be a function of the insulation. That is what ampacity charts tell us.
The ESCs are seeing 1/4 of the total current, so it is more reasonable. The three phase side even less. They are sized by RC standards… For better or worse, but are probably OK.
I think the greater concern here is anything near the batteries. That will see 150A (2 parallel batteries), or 300A (single set of batteries).
The difference between crusing power and WOT is a lot. 3X difference or more. At cruise, it is about 100A total if I recall. So only 50 amps per battery (assuming 2 parallel batteries), and only 25 amps per motor. That is unlikely to produce much heat.
I worry about a user that wants to do full throttle to climb as high as they can until the battery is depleted. Its a totally different use case and I worry the wiring is not up to the task.
Certainly, by accepted engineering standards it is not up to task.
Recall that heat produced is a function of current squared. It is not a linear relationship.
not much you can do with ESC, they should be fine on their own. Its the wiring from battery to ESC that need to be beefy, really just the battery, its power leads is the main weakness.
My amp meter is measuring the current to one motor so the 80 to 90 amps is already 1/4th. The chart above shows 12awg at 200 degrees C with only 55 amps and I often run 80 to 90 and can’t feel any heat through the insulation.
That’s 320 to 360 at the batteries but I run two sets in parallel which cuts that in half (160 to 180) and I have 8awg wire there. The chart shows 8awg at 200 degrees C with only 100 amps and I pull 160 to 180 amps through them and never feel any heat through the insulation or at the connectors.
I should also note that I keep all my wires as short as possible which probably helps. But how much does that help? I even cut the wires in half on my batteries… mainly to insure they stay out of the propellers but also to handle current better.
At level flight I pull about 30 amps per motor which is 60 per battery and 120 total. If I was lighter on my wing that total would probably be closer to 100 like you said.
The chart shown above lists the required temperature rating of the insulation for continuous operation, not the temperature of the conductor itself.
Note that ampacity is not a function of wire length. Rather, it is a function of cross sectional area. Really, heat generated per area.
By reducing the wire length, you are reducing the total resistance of the wire, which is good for performance, but you are not improving the ampacity.
I believe your observations that you don’t feel much heat. But you are not measuring in real time. I^2 R losses, are by nature of course, exponential. The difference between 70% throttle, and 100% is massive. A lot more than say, 40% to 70%. I expect the wires to dissipate that heat quickly to the other components - they are great conductors after all - once the load has been removed.
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Yes I did. They work well with the following caveat:
Make sure the plug is fully connected before running the unit (there a tight fit)
In my case, it was only half way plugged in (didn’t notice) so full current was running through the resistor inside the plug. Cooked it - chop off and replace (a lot more work than it sounds).