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SkyNorth posted .1 ohm as the value. He designed the board so he should be correct. He may also have a source.
Having a source will be good for others as this can happen of DIY mods go wrong.
Of course having Mike verify the value is good insurance since HK did produce the board.
SM


Sent from my iPod touch using Tapatalk, small keys and a big finger.

0.1 ohm is the value.

Mike.

If there is a short during dIY, shouldn't the fuse blow first?

KAL's post above is a well known industry saying, which doesn't exist without a reason.

Having a fuse is better than having no fuse, but it's very common for another actually weaker or less abuse-tolerant component to give up first.

The shunt will blow quicker than than fuse because it is smaller , the fuse has a larger thermal mass to heat up.

At 1A draw, the shunt dissipates
0.1R @ 1Amp = 0.1Volts
0.1V x 1 Amp = 0.1 Watts
So
a 1/4W , 0.1R , 1% in a 0805 package was chosen
Shunt Digi-Key Part Number
P100LLCT-ND

What is the fuse doing there then? Sorry about my ignorance but I really don't understand it..

SkyNorth wrote:The shunt will blow quicker than than fuse because it is smaller , the fuse has a larger thermal mass to heat up.

At 1A draw, the shunt dissipates
0.1R @ 1Amp = 0.1Volts
0.1V x 1 Amp = 0.1 Watts
So
a 1/4W , 0.1R , 1% in a 0805 package was chosen
Shunt Digi-Key Part Number
P100LLCT-ND

I would have thought that the resistor would be fine all the way up to a current draw of 1.5 Amps where it would be rather warm if that current was on a continual basis and much more than that on a pulse/temporary short circuit situation that would present itself before the fuse failed.

IMO the thermal mass of the fuse (assuming a fuse rating of around one Amp) would be far lower than an 0805 package, if you take into account the solder joints and the PCB pads that would have some thermal mass that would delay the destructive breakdown of the resistor to a value below that of the fuse. Hopefully this is the case or something hasn't been taken into account to allow for the fuse to blow instead of something else like the current measuring resistor.

Its a 170'F flat thermal fuse soldered directly to the pcb . ..its not a 1A glass fuse ..there is no current limiting fuse. (glass fuse is in charging circuit)
The shunt will handle 1.5A , we are not talking about 1.5A more like 15 - 150Amps !
The Life/Lipo can deliver a Huge amount of current in a short condition. The thermal fuse protects the traces on the board from being burnt off if there is a short.

There was either a bad solder on the resistor , or a bad part.
If the shunt was burnt (hole in center) then there WAS a short of some type

I have not tried OR RECOMMEND hot swapping the RF Modules. This might be able to create a surge or current loop that could draw excessive current

If you do blow the Shunt resistor , there is NO problem in just shorting it out ..Of course you will loose the ability to measure the battery current draw.
The Thermal fuse is still in place , and will protect against another short