How-To: Anti-Spark XT-90S Loop Key

Dumb question, but how did you urethane it so well?

About 30 coats heh heh heh. No, I’m not exaggerating.

I mean like, did you dip it, or brush it on.

My initial thoughts would be to dip out of a larger can, your bottle just seemed like it didn’t have a large enough opening to dip it in though.

The other angle is, if something goes wrong in storage or charging, the fuse might save your house, family, and multi-unit domicile co-inhabitants. :slight_smile:

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That’s why I fuse the charging :wink:

For wires and loopkeys and things needing physical abrasion resistance I use

MG Chemicals Urethane Conformal Coating in the 55ml brush-on bottle

But for PCB waterproofing I prefer

MG Chemicals Silicone Mofified Conformal Coating in the 55ml brush-on bottle

except on heatsinks, then

MG Chemicals Acrylic Conformal Coating in the 55ml brush-on bottle (because it’s super-thin)

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You just put a fuse of a rating slightly higher than your charge rating on your positive charge line?

In general, fuses should be rated to protect the wires behind it.

In this specific case, I’d fuse at the amps of the lowest component. Usually this is the 5.5mm dc jack. Next is the BMS charge max, then usually the charge wires (both positive and negative – it’s a circuit).

Fuses have some built-in room over their rating. If you oversize your fuse, it won’t kick in in time to save your parts. (this may be true even if you perfectly size your fuse)

For example, for this specific mini blade fuse:

The Time-Current Charactistics table says:

  • 110% of Rating: 100h Opening Time Min
  • 135% of Rating: .75sec opening time min, 120sec opening time max
  • 160% of Rating: .3s/50s
  • 200%: .15s/5s and so on.

So a 5 amp fuse will happily pass 5.5a most likely indefinitely, and will allow 6.75amps for up to 2 minutes.

(sorry I’ve been reading about fuses again)


No apologies. In my head I was thinking an 8 amp charger and maybe a 10 amp fuse as a reference point so good to know. You’d think chargers would just come with a fuse built in

chargers usually have a fuse, protecting the charger and the mains power. :slight_smile:

Ok that makes much more sense to me. @b264 you’re referring to just fusing the charging board/port side correct?

I usually put the fuse on the negative line, but yes. Either one.

Yes, just the charge jack on the board.

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Do some BMS have a built in fuse? This seems common sense for charge only ones given they already know what rate they’re charging. I imagine all battery makers would want to include this to protect their packs.

No BMS I have ever seen is “charge-only”

They just have very low discharge rates like 10A or less, and we don’t use that port.

“Charge-only” is more how you wire it up and not how the BMS is made.

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As i don’t want to cut my batteries leads, if i put bullet connectors where the blue arrows are is there any downside to this or reason not to?

and is this correct loopkey? one side goes direct to battery and the other to the vesc.

Charger cable would be soldered onto the vesc wire and then in a bullet connector

Edit: I’m aware the wiring colours don’t match up but i don’t see that as a concern for this

More places for shorts and disconnects and loss of power due to resistance. Use big bullets.

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Am I better off cutting the battery wire and just going with an XT-90?

It’s 4 mm bullet already so if better to use big bullets i’d need to change that anyway

These are the types of questions we all ponder for days. :slight_smile:

4mm is not that big. 5.5mm or bigger will have better retention. If you can use shrouded bananas like XT150 even better, but XT150 are chunky.

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The XT90S with the green stripe needs to be the loopkey. Put the male (without the green stripe) on the board. Also put a fuse on your charge port negative line.

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keep seeing mixed opinions about this - does it really matter if it’s the loop or on the board?