The sense charging cable

[PaPaRJW]

Another cable failure. Two now since I bought it 6 months ago.  Fitbit are sending another one.  I’m told it is the same design, so not confident of it lasting, they are.

Anyone have success with other ways to charge.?

[KB9WNS]

You can measure the temperature of the spring in operation if it is carrying current, sometimes it will sometimes not depending upon whether the gold plated contacts are touching, by supplying a constant current and measuring the voltage drop across the spring.  The electrical resistance of the spring will increase with temperature which will result in a measurable increase in voltage of the constant-current power supply.  The contact pin housing is gold plated inside and outside. Gold is highly reflective of IR energy in the 1 to 10 micrometer wavelength region and the contact housing will retain the heat very well. 

I found similar parts, from "Mil-Max" on Mouser that have a current rating of 2 amps.  The Sense's charge current is about 320 milliamps so plenty of spare capacity.

My partner still has a Sense, mine has died due to a failed screen (still sort of operates), and we have a bunch of dead chargers from FitBit and Amazon.  Might be worth a try to buy some contact pins, $0.45 each, from Mouser and try it on my old Sense and one of the dead chargers.

[Guy_]

@KB9WNS- if you have dead charge cables it would be great to discover the real reason for the pin sticking. I don't have any to experiment with.

I do measure 340 ma when the wifi connects otherwise it runs at about 300-310 ma at full steam.

How about a USB fuse box which cuts the current in excess of 340 ma that can be reset, then the cable can be used safely with any good 5V charge supply.

[KB9WNS]

"DROK" on Amazon has low cost current-limited power supplies that can be programmed with the 350 milliamp limit.  I am going to order some of the contact pins from Mouser and do some additional testing.  A 2 amp contact should not have any issues with charging at 340 milliamps.

[KB9WNS]

For those who have electrical knowledge this will work as a current limited charger.  Use a 6 volt 1 amp wall-wart power supply to power it and set the voltage to 5 volts and the current limit to about 350 milliamps.  You may get the "slow charging" message.   https://www.amazon.com/dp/B07JZ2GQJF/ref=emc_b_5_t?th=1

[Stebit]

Thank you KB9WNS. It's amazing that it took an aerospace electrical engineer to get to the solution. It's been three months since I read your information and during all that charging time, I have not had single failure. The solution is indeed as simple as using a low power charger.

I hope more people see this solution. Over the years I probably could've purchased another Sense with the money I wasted on cables.