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Charge cable PSA - check the fuse if charging slowly

jollie89

Member
Jun 1, 2019
14
1
Cambridge
Just a quick PSA regarding the EVSE that comes with teslas. The charge rate kept dropping to 5 Amps (4 miles per hour) when charging on the 3-pin charge cable at home. I assumed it was the wiring in my garage causing too much of a voltage drop. However, it happened even from known-good sockets, and I noticed the plug was very hot (more so that normal). I check the fuse in the 3-pin plug.

Firstly, it's fitted with a 10A fuse (just saying). Also, the plastic clip around the fuse had perished a little. Swapping out this fuse immediately resolved the low charge rate issue.

Just wanted to mention it so if you see a similar issue you know to check if the fuse is wearing out. You may also want to carry a spare fuse in case it happens on a road trip. Could be the difference between 100 miles and 50 miles (or zero) of range added over night.
 

Watts_Up

Active Member
Mar 4, 2019
3,457
2,358
In a galaxy far, far away
The fuse is in the UK 3-pin plug itself. It's designed to protect the wiring in the house.
I had in fact one of those plugs with a ceramic fuse inside, the plug adapter was bigger than my USB charger.

I am just puzzle how you can still get slow charging after the fuse blow up?

I was thinking that the fuse was protecting only the electronic part of the UMC charger,
but the power was still going across the power line thus letting having a slow charging?

Note: By curiosity I would be interested to see how the UK Tesla UMC compared with the US Tesla one?
I checked the Tesla UK website, but I cannot find a charging store page like in the US?

The US wall UMC plug adapters contain also a resistor which is use to determine the Amperage,
but also (I assume) can be used to detect overheating caused by the plug not correctly insterted.
 

jollie89

Member
Jun 1, 2019
14
1
Cambridge
I was thinking that the fuse was protecting only the electronic part of the UMC charger
I checked this - the fuse is designed to protect the cable to the device if the device draws too much current. I believe it's part of British standards. As you suggest, the UMC can take way more than 10A, so I would have expected at least the maximum allowed (from a regular 3-pin socket) 13A.

I am just puzzle how you can still get slow charging after the fuse blow up?

In my experience fuses are very crude devices not to be relied on. They blow eventually even when used below their rated limit, and the limit is not precise, so sometimes they will not blow when they should.
Often they are designed to 'blow' slowly, so that they aren't too sensitive. However, the Tesla software detects high resistance and limits the current. I suspect this system saved the fuse when it was halfway blown!

Here's the little fella:

hqukXJb.jpg
 

jollie89

Member
Jun 1, 2019
14
1
Cambridge
The UK UMC I'm referring to looks like the bottom one:
67631007_10162010299265231_3768584372014284800_o.jpg


The moulded 3-pin plug is basically the same as this one (on the pictured one the fuse holder is red):
3_PIN_MOULDED_UK_PLUG_MAINS_POWER_CABLE_ASTA_BS_1363_1_JF_06A.jpg
 
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