Important! Wire sizing for current draw

You are correct to raise the concern. However, I am not going to pretend its outside the capability of anyone. That is a condescending attitude that gets no one anywhere.

You are correct that soldering would not be used in automotive or energy storage. Which is the industry I have worked in for 25 years. It is however almost universally used in “hobby” and consumer electronics packs.

As you probably know, there will almost always be a solderable tab welded to the discharge tabs. They weld “solderable” tabs the the otherwise non solderable tabs for a reason. To make them, well, solderable.

The Bonka packs as used by most here are hobby packs, and built as such. The discharge leads WILL be soldered.

60W is exceedingly adequate for even significantly larger conductors given you have a tip with the thermal capacity. I for one have done it, and with much larger conductors that we are dealing with here.

I must also point out that your comment of 300A through 10awg wire is somewhat incorrect. While 300A through 10awg is excessive, your reasoning was due to fusing. As you must know, the AWG chart specs are based on PVC insulation. Not silicone. The fusing current is far higher with silicone insulation. Which is essentially universally used on hobby packs, and will most certainly be used for the power distribution in this system. You have referenced evidence (the chart) which basically does not apply for anything other than getting the cross sectional area of the conductor of a particular gauge. The fusing specs do not apply.

As these are paramotors, safety and concern is paramount, agreed 100%. However, I have yet to see concern in areas where it would be better placed. Such as interconnects. I have seen some using rather questionable wire terminals for their interconnects. This is of much greater concern IMHO.

There is far greater concern of the house burning down with a loose connection of unknown state in the pack than there would be for him to repair the pack. My extensive experience in the subject suggests to at the very least, open the pack, and ensure the conductor isnt going to short. Leaving it in that state is a much greater fire hazard.

Now you say I am right to raise the concern? But a few posts ago you were saying I was overly concerned? What are we arguing about :slight_smile:

Never said that.

Sorry, I am really questioning your “expertise” now. Fusing is where the wire acts like a FUSE… that means it melts.

Other ampacity charts are rated for when the insulation fails or reaches some high temperature. That occurs at a much lower temperature, and current, than the fusing temperature!

Yes, Silicone insulation can take higher temperatures, but it melts well before copper! That is the point… the insulation will fail at LOWER currents than even the 333A fusing current. I made this clear in my first post.

Further, such fusing current is for the conductor in free air, where it gets cooling. Being in insulation, and even worse in a bundle, only makes it worse.

I am not interested in arguing with you, but please do not criticize me for encouraging people to be cautious.

Yes you are absolutely correct. The danger of wire fusing with PVC insulation VS silicone is far greater. The danger isnt that the wire fuses, its that as fusing takes place, the insulation melts as you have stated, which leads to potential secondary shorting etc. Silicone “melts” at a much higher temperature. It actually doesnt “melt” in the manner plastics do, and as such are safer in over current conditions, or a fuse event. This is precisely the reason silicone insulated wire is used in these sort of applications. I could have been more selective in my wording to convey context better.

The chart assumes wire placement in a wall, with no air flow at 25C ambient, with plastic insulation. Whether you want to conceded to that or not, it clearly states the insulation type is a determining factor in these ratings.

I will point out that silicone is however not nearly as mechanically resilient. It is prone to abrasion and tearing. This is the reason it is not typically used outside of hobby use. So be careful using it around edges of carbon etc.

I didnt criticize expressing caution, I believe I expressed caution as well. Rather the overly cautious approach. Which can lead to dangerous consequences in it own right. Discouraging this guy from repairing his pack could be an example of such.

However, we can both just simply agree that 10awg is a bit on the small side.

Again, the fusing current is when the conductor itself melts. At that point the insulation has already failed. PVC or silicone. Literally at these currents the copper is melting. That won’t change based on the insulation that was once covering it. To imply that the copper in silicone covered wiring will fuse at a different temperature than other insulation is dubious.

Sounds like you are being an alarmist.

I may have missed it, but the chart does not specify the temperature in which copper fuses, only the current at which this temperature is apparently reached for specific gauges, and yes , the insulation, as well as ambient temp, and airflow does plays a role in the rate at which this temperature is reached.

In regard to the second part. Have you ever used silicone wire? Have you ever used silicone wire around relatively sharp abrasive edges? I assure you it DOES fail mechanically.

Is it not a concern to prevent its mechanical failure in the air than the slight risk of exceeding its ampacity for a short period of time in significant airflow? That is not alarmist at all. I didnt start a thread to point out an issue that is just barely an issue. It was an aside , that is just as much of a concern , if not more so in this case.

Even strictly going off the chart , 10ga with a fuse rating of 333A, and a peak of 300A on the paramotor, that gives you an overhead of 11% on ampacity. Which is a bit too close for my comfort personally, but will suffice given the temperature rating of silicone insulation, and the application. With PVC at 300A it will most certainly fail regardless if it fuses or not.

I think you are confusing “ampacity” and fusing. Not the same thing. The insulation is defined for the ampacity rating, which is the current it can carry before the insulation gets to a particular temperature, as defined by the table.

333A is NOT the ampacity of any 10AWG wire! Not anywhere near that. The ampacity will be something much much lower. 300A is way above the ampacity rating.

333A is the fusing current when copper melts. That is independent of the insulation. Those tests are performed on bare wire it appears. I recommend you read the references for the fusing currents.

You want to miles away from the fusing current. 10% isn’t even close. 50% isn’t even good! That was my whole point, which you have missed. If we are this close to the fusing current, we have already grossly exceeded any ampacity rating that any 10 awg silicone covered wiring has.

dude, I was joking with you, relax man.

@Pdwhite - Have you heard back from Bonka on why the gauge was wrong on many of the batteries?

I would like to know as well.

Unless they have the wrong pictured unit for the switch, it’s not 300A rated. The lugs on that unit are marked for 50 amps and the device is rated for 200.

250A-350A should be 6AWG.

Looks like Dave’s switch failed, per his thread. Indeed a more robust solution is required than the supplied switch.

I’m quietly a bit sus on that switch and am considering alternative options.

My concerns go beyond it’s rated current capacity. I believe that the initial in-rush current as it makes contact is quickly destroying the internal contacts. It’s all downhill for the switch from that point.
I have been looking at using a pre-charge resistor to fill the capacitors of the ESC before turning power on, negating that massive sparking surge at the beginning.

I then started thinking about just doing away with the power switch, direct plugging the batteries in using some of these anti-spark connectors:
OSE 8.0mm Anti Spark Connector : Male & Female Pairs | Offshore Electrics.

Throttle signal wire can be run through an e-stop switch for emergency prop shutdown. I’m sure between us all, we’ll find an elegant solution

Will be testing these options in due course and report back.

Yeah, I’m going down a similar path with the pre-charge switch - that’s pretty important. As I look at the contacts of even a lightly used switch, the arcing/pitting is evident, which leads to higher resistance, which snowballs to a melting switch I believe.

I put in a secondary PWM loop that I can yank out while in the harness to cut off throttle. Doesn’t help if there is a short in the system (wish I had a battery cutoff I could throw from the seat), but it does help if the sw in the throttle crashes or something…

Maybe relays could be sourced to do precharge and main contacts. The current requirements, 300+ A, are similar to those in automotive.

Suppose when the batteries are plugged in it would energize a low voltage circuit that would drive the contactors. A low current (could be mounted anywhere for more conveinence) switch would engage precharge and then mains. Maybe some arduino to control all of the timing and logic.

Pre-charge resistors are the right way to do it. The electrolytic DC bus caps are not huge, so a resistor would be fine. Avoid thinking that cutting the throttle wire is the right way - a failed FET in one of the B6s will quickly have the whole ESC ‘letting the smoke out’, and you need the contactor to shut that down (or fast fingers on your battery connectors) If you go with the arduino/a.n.other controller, put a DC bus current monitor in also to drop out the contactor when the current exceeds 500A. Stay safe!

@Codemonkey you’re correct re the FET failure or other electrical short mode of failure. Another mode of failure could be SW glitch in the throttle with a stuck PWM, or a busted potentiometer that goes full throttle or similar. A PWM cut switch would end that situation (a contractor would do that too)

I’ve been looking for 48V/400A contactors, which seem to be found in the marine/ebike world - but they’re all like 1-2 pounds. Anyone got a lighter one we could use?

Big contactors are heavy beasts. Is it worth getting 4x 100A relays?

We would only need to switch one side (high side, for example). With precharge, that would be 2 contactors.

The precharge contactor can be a lot smaller, much less than 100A.

Main contactors there are a decent selection of options, this is 12V coil, and rated to 500A:

Yes, these things are kinda heavy. I just spent 2 minutes searching, might be much better options somewhere…

This might be good:
http://www.evwest.com/catalog/product_info.php?cPath=2_13&products_id=102&osCsid=nlujttcpqdso2j76n3sac69376

they all appear to weigh slightly less than 1 lb. How much does the switch weigh that is included on the openPPG?

Did a bit more searching… the digikey ones are all >$1000, which is insane.

Found this:

Much smaller, certainly cheaper! Can get a 48V coil on the solenoid which is convenient, and should bolt right to my bus bar configuration. Don’t have a weight published, so I’ve asked. < 50W on the coil side, so would need either a smaller switch or relay to drive it and the pre-charge. I wonder if the bus caps and pre-charge resistor would actually self-time the drive side…

I was envisioning the precharge circuit opening after the mains are closed. That way, whatever power resistor limiting the precharge current is not wasting energy, however small, and getting hot. This would require some logic to drive it.

I feel that it would be fairly simple to have an arduino uno, with a dual relay shield and voltage regulator (total cost <$20). The shield would drive the precharge and mains in sequence and then disengage the precharge circuit. This would all happen in a second or two.

Would also require flyback diode on the main contactor.

Using 12V coil voltage opens up a bunch of ~$100 options made for automotive applications that have very low current draw.

EDIT: I had originally assumed that most systems open the precharge circuit after closing the mains, now I am am second guessing my memory. Maybe not. Once the bus is energized, the current through the precharge circuit would be very small, so it should not waste much.