Ingineer wrote:My take is that the 6.6kW upgrade would be tricky. First off, it would require 2 beefier wiring harnesses, both running the length of the car; one from the J1772 inlet to the charger (EMI filter) and one from the charger to the HV junction box. The reason is the size of these wires appears to too small to support anything larger. It might also require an upgrade to the J1772 inlet itself.
It would also require draining the cooling system and crawling under the car to disconnect the lines.
I think that’s why Nissan doesn’t want to talk about a 6.6kW upgrade. It is too integrated into the design to do profitably. Throw this thing away and buy a new one. New harness, new EMI Filter, change software, teach it how to read the pilot signal.
And dealer Labor for doing all this. You'd faint when they show you the quote.
Huge mistake not to go 6.6kW fromt he start.
Actually you might not need to change anything (besides a thermostat or two) about the wiring harness to get up to 6.6k. Read on if you want to know why...
Anyway despite the above, This still Sounds to me like a classic case of penny wise but pound foolish, to have the car 6.6k ready by ac house wiring standards would have cost maybe $10 in electric wires (likely a lot lot less in reality since really only 4 of the wires needed to be a slight bit beefier) but all is not lost...
Generally for chassis wiring 10 guage would have gotten you the 33amps continous needed to run 6.6kw albeat with a bit of efficiency loss so long as ambient temperature is below 135 degrees and the charger can handle a bit of voltage drop. Me, if I were doing a rig of this type I would have used much beefier wires than those considered necessary because they are more efficient and more expandable in the future.
12 guage wire is officially rated at 15amps continous duty by most but not for any official failure reason, 10amp or 15amp ratings associated with 12guage wire have to do with voltage drops over 50' and 100' and not any actual failure risk.
I would recommend reading this.
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There are also others on this subject with a simple google search of 12 guage amperage rating
Generally 12 guage wire can easily handle 23amps continous, this means a little south of 5kw with the existing system is just fine and dandy, and the truth is it can conservatively handle loads up to 41amps depending on temp and duration and of coarse the coating on the wires. It is worth noting that alternators on many cars rated at a little more than 60amps many times only have 12 guage wiring, this is because efficiency is not a concern and the duration at 60amps should not be continous, though it may have to output that rate for hours at a time. The odd part is I have seen a couple hundred amps forced through 12 guage without it blowing up, the risk is fire going way past its rating.
The main issues with this will be interconnects and plugs which are always failure points, the wire itself will likely not fail (even if you were to force enough juice through to burn off the coating).
The cooling system is a non-issue, if the 6.6kw system is efficient and the emphasis stays on efficiency you can make a 6.6kw system that likely dissappates no more heat than the 3.3kw and even if it does make more heat it still doesn't matter because a thermostat could be setup to protect the system such that it will run full blast until its temp raises to certain point then it would slowly derate to prevent overheating.
The same concept would be needed on the wiring, a temperature module near the "J" connector (which should by its own standard require at least 50amp connectors right?) and inside the car near any plug in connectors would be needed.
Because continous is a good long time, I would estimate the wires would not notice 4 hours at a spat and if they did reach max temperature (whatever that is) 3.5 hours in, what would you care if the charger had to derate to 4.5kw?
I would strongly recommend nissan and folks here (who have access to the wiring harnesses) do some failure testing monitoring the temperature of the chassis harness while in a car (to simulate the stuffy environment) to see how hot the harness gets at the 33 or so amps that would be needed for 6.6kw with wire losses and whether or not it fails in any way. Remember that there are many wires rated at 200c or more (sometimes ones that aren't are still made of materials good to that level of abuse) so it is well worth long term testing to see if the wires fail or if there are plug in connectors that would need replacement (much simpler than a whole harness to beef up a connector)
Any takers? I am an engineer and I disagree that a wire guage automatically dissallows a certain use, whether it is safe or not depends on monitoring and the material composition, chassis wiring has much different specs than household wires and despite what some may say here, auto wires should be good up to at least 240 deg F without issues or somebody screwed up royally.
For example, my father has a 6 year old cheap 48v 25amp chinese battery charger in his EV, it has 18 guage (or smaller) wire through out and many very underrated parts, it has been used most every day for years and still works fine (though the fan is getting noisy) It keeps working because once it hits its temperature limit it derates, oddly though it usually doesn't hit that point and has been abused for years with improper ventalation. Internally it does have a wicked voltage drop and is not that efficient but it was cheap.
So please, don't give up hope, I think this problem is being made more complex than it really is and if Nissan is reading this
PLEASE SPEND THE $0.50 and use bigger wires in your harnesses! Don't skimp on a 30k car! Components should be overrated not just meet spec, although I guess you can say you exceeded the chassis requirements but still, why not have the extra efficiency and piece of mind.