Charger grip for XT60 ports

[harrisonpatm]

My 24S LiFePO4 e-moto uses an XT60 port for charging. I had a learning curve trying to avoid sparking when connecting the charger. First I got those anti-spark XT connectors; they failed immediately. I looked into a couple of anti-spark circuits that I could buy, but even 20-40 USD seemed a bit expensive to me. So what I decided to do was make a simple XT60 M to F adapter with a toggle switch on the positive line. Switch off, plug in the charger, switch on. Therefore, I didn't make an anti-spark anything, all I did was move the spark to a toggle switch. That way, I can purchase an over-specced switch for my needs that can handle the spark, and even if it eventually fails, all I have to replace is a cheap switch. Works for me. I wrapped it up in electrical tape.

Then I got a 3d printer last month and have been learning about it, so I made a sort of charging handle for my contraption. I thought I'd share with the forum, I bet there's a few members here that use XT60 ports for charging and might enjoy a nicely-shaped handle for charging their EV. Made a simple wall-mount holster for it, to kind of replicate the gas pump experience. Please excuse my messy print, I'm still learning the hobby and figuring out my settings. Would love input on the design.

https://www.printables.com/model/349398-xt60-switch-handle-for-charging

 

[fechter]

You could put a resistor across the switch and make it actually anti-spark.

 

[harrisonpatm]

You could put a resistor across the switch and make it actually anti-spark.

Absolutely, planning on it. Just didn't have one on hand at the time

 

[E-HP]

You could put a resistor across the switch and make it actually anti-spark.

Absolutely, planning on it. Just didn't have one on hand at the time

If the switch you added turns the power on/off, then you may need a separate momentary switch in series with the charging resistor, so you can press the button to pre-charge before flipping the power switch.

 

[99t4]

What is the function of the gas cap?

What voltage is your battery?

 

[E-HP]

What is the function of the gas cap?

What voltage is your battery?

He said "24S LiFePO4" so 3.2 x 24 = 76.8V nominal I think.

 

[harrisonpatm]

You could put a resistor across the switch and make it actually anti-spark.

Absolutely, planning on it. Just didn't have one on hand at the time

If the switch you added turns the power on/off, then you may need a separate momentary switch in series with the charging resistor, so you can press the button to pre-charge before flipping the power switch.

I'm not sure that's necessary in my case. If I put the resistor across the switch, and the switch is in the off position, plugging in the charger will place the resistor in series with the whole circuit. Therefore, switch in off position = precharge. So, switch in off position, plug in, wait 2 seconds, flip the switch to on. When the switch is in the on position, current takes path of least resistance and bypasses the resistor.

Either way, I found a 1Kohm resistor in my stash and tested it, so I know it works, at my voltage for my use. And like I mentioned earlier, I thought it would be useful to share a neat handheld XT60 switch that the forum can modify however they'd like. If you just use the switch, it's still effective at protecting the XT60s from spark by directing the spark to the switch.

 

[harrisonpatm]

What is the function of the gas cap?

For giggles. It was an 84 Honda 450 conversion https://endless-sphere.com/forums/viewtopic.php?f=12&t=117496, and I thought it would be fun to turn the original motorcycle's gas cap into the charge port.

 

[E-HP]

I'm not sure that's necessary in my case. If I put the resistor across the switch, and the switch is in the off position, plugging in the charger will place the resistor in series with the whole circuit. Therefore, switch in off position = precharge. So, switch in off position, plug in, wait 2 seconds, flip the switch to on. When the switch is in the on position, current takes path of least resistance and bypasses the resistor.

Either way, I found a 1Kohm resistor in my stash and tested it, so I know it works, at my voltage for my use. And like I mentioned earlier, I thought it would be useful to share a neat handheld XT60 switch that the forum can modify however they'd like. If you just use the switch, it's still effective at protecting the XT60s from spark by directing the spark to the switch.

That will work, but you're just moving the spark/arc to the switch contacts. That's OK if the contacts can endure several actuations. The pushbutton in series with a resistor will have very little flowing through is, so no issues.

So depending on the quality of the toggle switch, it could be damaged from arcing too.
https://youtu.be/vcKGbWxLL7s?t=18

I use an AC breaker as a switch, since they contain contacts similar to those on relays, but I added the pre-charge resistor and pushbutton when I swapped it out a few months go. However, I found I didn't really need it, since the 40A breaker contacts were still in good shape after several thousands of actuation, during the autopsy.
https://endless-sphere.com/forums/viewtopic.php?f=3&t=117505&p=1730266&hilit=breaker+contacts#p1730266

An AC breaker won't trip under DC current, so it works great as a switch, and can support much higher current than the rating (mine has survived 120A).

 

[harrisonpatm]

I'm not sure that's necessary in my case. If I put the resistor across the switch, and the switch is in the off position, plugging in the charger will place the resistor in series with the whole circuit. Therefore, switch in off position = precharge. So, switch in off position, plug in, wait 2 seconds, flip the switch to on. When the switch is in the on position, current takes path of least resistance and bypasses the resistor.

Either way, I found a 1Kohm resistor in my stash and tested it, so I know it works, at my voltage for my use. And like I mentioned earlier, I thought it would be useful to share a neat handheld XT60 switch that the forum can modify however they'd like. If you just use the switch, it's still effective at protecting the XT60s from spark by directing the spark to the switch.

That will work, but you're just moving the spark/arc to the switch contacts.

Well, absolutely, that was kind of the impetus of the switch design: saving the XT60's from sparks and moving it to the switch.

However, as far as I understand it, the spark occurs because the capacitors in the charging device charge instantly once connected to the battery. The resistors slows down that current. So if my design operates as intended, the switch in the off position, connecting the battery and the charger, allows the resistor to slowly charge the caps. Then I switch the position to on and bypass the resistor, and now the caps are (mostly) charged, so no spark.

That's as far as I understand it anyway, and that's what I've seen (and heard) in my tests, on both my chargers and my motor controller, which also uses a precharge resistor. Correct me if the above paragraph is a wrong understanding.

However, even if I am totally wrong in my resistor setup, your point is totally understood: my original point was to move the spark from the plug to the switch, and it worked great for 4 months before I disassembled for the winter. Switch is still working. I like your point on using an AC breaker, but I also like the aesthetics of having something small and hand held. My design fits nicely into my hand, plugs in easily, and I can easily reach the switch with my thumb while it's still in my hand.

 

[E-HP]

Well, absolutely, that was kind of the impetus of the switch design: saving the XT60's from sparks and moving it to the switch.

However, as far as I understand it, the spark occurs because the capacitors in the charging device charge instantly once connected to the battery. The resistors slows down that current. So if my design operates as intended, the switch in the off position, connecting the battery and the charger, allows the resistor to slowly charge the caps. Then I switch the position to on and bypass the resistor, and now the caps are (mostly) charged, so no spark.

That's as far as I understand it anyway, and that's what I've seen (and heard) in my tests, on both my chargers and my motor controller, which also uses a precharge resistor. Correct me if the above paragraph is a wrong understanding.

However, even if I am totally wrong in my resistor setup, your point is totally understood: my original point was to move the spark from the plug to the switch, and it worked great for 4 months before I disassembled for the winter. Switch is still working. I like your point on using an AC breaker, but I also like the aesthetics of having something small and hand held. My design fits nicely into my hand, plugs in easily, and I can easily reach the switch with my thumb while it's still in my hand.

That will work. So this is functionally just taking the place of the pre-charge XT connector, and not for switching. In other words, place switch in the OFF position (with the resistor between the terminals) when connecting the battery, then flipping the switch to ON after a few seconds, depending on your resistor. In my case, it looked just like your configuration to begin with, since I was using the breaker/switch to turn everything off. So I added the resistor/push button combo across the switch terminal.

I used this smaller breaker to replace the old one, but I just now realized why it tripped unexpectedly a few times.
I thought my leg rubbed up against it. Reading the description more carefully, it's actually an AC/DC breaker. It tripped a couple of times with short 80A peaks, and a couple of times when over 40A continuous for a short period going full throttle.
https://www.amazon.com/gp/product/B07MYY14MX/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&th=1
It's pretty tiny; about the size of a matchbox (can't recall the last time I saw a matchbox though).

 

[harrisonpatm]

Well, absolutely, that was kind of the impetus of the switch design: saving the XT60's from sparks and moving it to the switch.

However, as far as I understand it, the spark occurs because the capacitors in the charging device charge instantly once connected to the battery. The resistors slows down that current. So if my design operates as intended, the switch in the off position, connecting the battery and the charger, allows the resistor to slowly charge the caps. Then I switch the position to on and bypass the resistor, and now the caps are (mostly) charged, so no spark.

That's as far as I understand it anyway, and that's what I've seen (and heard) in my tests, on both my chargers and my motor controller, which also uses a precharge resistor. Correct me if the above paragraph is a wrong understanding.

However, even if I am totally wrong in my resistor setup, your point is totally understood: my original point was to move the spark from the plug to the switch, and it worked great for 4 months before I disassembled for the winter. Switch is still working. I like your point on using an AC breaker, but I also like the aesthetics of having something small and hand held. My design fits nicely into my hand, plugs in easily, and I can easily reach the switch with my thumb while it's still in my hand.

That will work. So this is functionally just taking the place of the pre-charge XT connector, and not for switching. In other words, place switch in the OFF position (with the resistor between the terminals) when connecting the battery, then flipping the switch to ON after a few seconds, depending on your resistor. In my case, it looked just like your configuration to begin with, since I was using the breaker/switch to turn everything off. So I added the resistor/push button combo across the switch terminal.

I used this smaller breaker to replace the old one, but I just now realized why it tripped unexpectedly a few times.
I thought my leg rubbed up against it. Reading the description more carefully, it's actually an AC/DC breaker. It tripped a couple of times with short 80A peaks, and a couple of times when over 40A continuous for a short period going full throttle.
https://www.amazon.com/gp/product/B07MYY14MX/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&th=1
It's pretty tiny; about the size of a matchbox (can't recall the last time I saw a matchbox though).

Good tip, it does look quite small, at least small enough that I could redraw the handle to fit it, if the switch ever dies.

 

[chuyskywalker]

Yeah, over a 52v nominal system, most of the market-ready anti-spark pre-charge stuff will only last a few insertions -- just not capable of handling the current from higher voltage setups.

I went down a few avenues recently on this as well (based on findings around here).

The idea of just bridging the contacts on the toggle switch with the right size resistor will absolutely get you what you want here.

 

[E-HP]

Yeah, over a 52v nominal system, most of the market-ready anti-spark pre-charge stuff will only last a few insertions -- just not capable of handling the current from higher voltage setups.

I went down a few avenues recently on this as well (based on findings around here).

The idea of just bridging the contacts on the toggle switch with the right size resistor will absolutely get you what you want here.

I wonder how much/little current continues to flow if the device always stays connected between the battery and controller, but with the switch open.

 

[harrisonpatm]

Yeah, over a 52v nominal system, most of the market-ready anti-spark pre-charge stuff will only last a few insertions -- just not capable of handling the current from higher voltage setups.

I went down a few avenues recently on this as well (based on findings around here).

The idea of just bridging the contacts on the toggle switch with the right size resistor will absolutely get you what you want here.

I wonder how much/little current continues to flow if the device always stays connected between the battery and controller, but with the switch open.

For this application, this is just between my charger and battery, which is only plugged in for charging. You're talking about a precharge resistor, I assume, across the contactor usually. So yeah, having a resistor across the leads 24/7 is a drain.

Easy to calculate though, I'll do it on mine. I have a 72v nominal, but lets call it 75V, that's a more accurate range that I keep it. I use a 1000ohm resistor as my precharge, across the contactor. V=IxR, so .075 amps. At 75V, that gives me 5.625 watts of drainage. Let's assume I ride 1 hour per day, therefore 23 hours a day the contactor is open and the resistor is "draining." That's 129.375wh per day. Might sound like a lot. Depends on your priorities. I have it constantly feeding the caps on my expensive controller, so I never worry about inrush current. I don't have a 2-4 step ignition sequence that includes a precharge circuit and a few seconds that I have to do correctly every time. Or, I don't have a relatively complex automatic precharge circuit, that could potentially fail. I know they can be made somewhat simply, I just mean, complex when compared to a single resistor that's terribly unlikely to ever fail. It's also only 130wh per day against a 5kwh battery pack, only 2% of it's total capacity. On a bike that is powered by free solar energy. I don't mind.

Plus, I doubt it's actually 5.6 watts continuous. The precharge resistor charges the motor controller caps. Once they're charge, the load drops, so it gets much less than 5 watts of drain. Yes, capacitors leak, but not continuously, not instantly. I haven't measured it myself, but it would be easy to check: stick a DMM set to amps between the resistor and the motor controller and watch it tick. If I had to guess, I'd say it's much less than 5 watts in real life, probably more like 1-2 watts. But even if it's 5, I'm fine with it.

 

[E-HP]

Plus, I doubt it's actually 5.6 watts continuous. The precharge resistor charges the motor controller caps. Once they're charge, the load drops, so it gets much less than 5 watts of drain. Yes, capacitors leak, but not continuously, not instantly. I haven't measured it myself, but it would be easy to check: stick a DMM set to amps between the resistor and the motor controller and watch it tick. If I had to guess, I'd say it's much less than 5 watts in real life, probably more like 1-2 watts. But even if it's 5, I'm fine with it.

I think it's only going to draw current at a rate equal to the caps discharging/leaking. I guess it could be measure, if the you set the multimeter on the current setting, but only insert it in the circuit after pre-charging. Might not even be measurable.

 

[fechter]

The easy way to measure the current is to just measure the voltage across the 1k resistor when it's sitting. 1mA per volt. You can do the math from there. If the controller is "off" the drain should be near zero.

 

[amberwolf]

Measuring actual current would be best, but some data points:

Typically the current drawn by a controller in the "off" state (no battery connection to it's LVPS, meaning the "keyswitch" wire is disconnected) is in the microamps, probably less assuming non-defective capacitors and FETs.

An "on" controller is probably in the dozens of milliamps.

Assuming a worst-case off current of 1mA, thru a 1kohm resistor, that's 1mA x 1kOhm = 1v. 1V * 1mA = 1mW. (assuming I can do math today, which is never a guarantee).

Assuming a medium-case on-current of 100mA, then power usage is a hundred times the off state, but still very small.

24 hours x 1mW is still only 24mWh, and even 100 times that is only 0.24Wh.

 

[harrisonpatm]

Awesome. I simply wanted to contribute an in-line XT60 switch, but I appreciate the confirmation that my always-on precharge resistor barely wastes any power. I was fine with 100wh, but Amberwolf's estimation of 24-240mWh sounds even better.

 

[amberwolf]

Been a while since I tested it, but IIRC my SB Cruiser trike's Cycle Analyst, two controllers and a DC-DC (well, an AC wallwart used as a DC-DC) driving an automotive relay coil don't use more than a maybe 300mA when left on. (the CA is zeroed to not count this current to make controller/motor testing simpler so I would have to use a separate meter to verify).

 

[E-HP]

Been a while since I tested it, but IIRC my SB Cruiser trike's Cycle Analyst, two controllers and a DC-DC (well, an AC wallwart used as a DC-DC) driving an automotive relay coil don't use more than a maybe 300mA when left on. (the CA is zeroed to not count this current to make controller/motor testing simpler so I would have to use a separate meter to verify).

So 300mA would be 3Ah in 10 hours, so a 15Ah battery would be dead in 50 hours, so if you’re riding at least every other day, then should be fine.

Personally I keep everything disconnected so I don’t have to worry about leaving my bike too long and kill an expensive battery.

 

[amberwolf]

So 300mA would be 3Ah in 10 hours, so a 15Ah battery would be dead in 50 hours, so if you’re riding at least every other day, then should be fine.

Personally I keep everything disconnected so I don’t have to worry about leaving my bike too long and kill an expensive battery.

Yes. Mine is a 40Ah, but I use a battery disconnect switch with removable handle / key both for that reason and a measure of security whenever I get off the trike, other than when charging (since charging goes thru the controller side of the CA shunt so I can track that or test / diagnose if needed...and the charger is hardwired to that point).