mark_hetho wrote: ↑Mon, 12 Nov 2018, 18:21
I guess the other way to work it out would be based on the charging time and capacity of the inverter supply smoothing capacitor. There is a trouble code for too long a (pre)charging time (P1A15), but the manual I have doesn't say how long. Given the time before the main contactor disengages without the precharge working it's maybe 7s.
The ohm value of the pre-charge resistor is likely not all that critical. The energy that the resistor has to absorb without exploding is fixed. So if you use a larger resistance, the current is less, but it persists for a longer time. If you use a lower resistance, the current is higher, including the initial peak current, but it doesn't last as long, so the energy is exactly the same.
I strongly recommend finding a resistor with a high pulse power rating, such as the
Tyco HS series. They can withstand 25 times their nominal power rating for 1 second. A typical pre-charge time is half to one second, to get to about 90% of pack voltage. That means a pretty high initial current, but the contactors are designed to handle hundreds of amps, so this isn't an issue. Using too high a pre-charge resistor risks the situation where current drawn by the motor controller and charger output stage causes a sort of voltage divider whereby the capacitors will never charge to the threshold value that the ECU is looking for, and pre-charge will fail.
Let's pluck some figures from the air. Let's say we want pre-charge in about 1 second (7 seconds might be a timeout value, well outside ordinary operation). Let's say we want to get to 95% of pack voltage (ignoring current drawn by the motor controller and charger output). So that's about 3 time constants. So we want the time constant to be about τ = 0.33 s. The formula is τ = RC or R = τ/C. Now for a wild guess at the total capacitance of the motor controller and charger output; I'll take 1000 μF or 10⁻³ F. So R = 0.33 / 10⁻³ = 330 Ω. If the capacitance is more than 1000 μF, then the resistance will have to be lower.
Now consider the pulse power. Initially, the capacitors will be at zero volts, so the full pack voltage appears across the resistor. Let's say it's 360 V. P = E²/R = 360²/330 = 392 W. That's a lot of power, but for a very short time. With a pulse power rating of 25, the resistor could be nominally 392/25 = 15.7 W, next highest standard value is 20 W. That's physically a moderately small resistor.
But if the capacitance is more like 5000 μF, then the energy the resistor will have to absorb will be five times greater. It will have to be a fifth the resistance (say 68 Ω), and the nominal power will have to be 78.5 W, next highest standard power is 100 W.
Some values are in stock in Australia from RS Components, like the
100 Ω 100 W part (but not the
68 Ω 100 W part). The latter is 5 working days delivery, compared to next day delivery for the former. Delivery to Western Australia may be longer. You'll have to decide if this is quick enough. Perhaps a local supplier would have stock you can pick up yourself, but it seems unlikely. It might even be worth gambling on the 100 Ω 100 W resistor being close enough to buy it in advance.
Make sure you have on hand wire, heatshrink tubing, and suitable lugs. I'm pretty certain that the wires to the pre-charge resistor can be seen in this image:
From
http://myimiev.com/forum/viewtopic.php? ... =10#p27408 .
The orange and red insulated crimped lugs would run off to the pre-charge resistor, sadly not visible in these photos. It looks like there is plenty of room to mount the resistor to the right of the contactors; it could be simply glued into place. It won't need a heat sink, and won't get more than warm to the touch. That way, there is no need to uncover the original resistor if it's hard to get to, though it would certainly be nice to know its value (assuming it can be read from the case).
[ Edit: I note that in the next post from the one linked to above, user Kiev asks for the value of that resistor. Sadly, as far as I can tell, his question was not answered. ]
[ Edit: nearest -> next highest. You don't want to go *down* in power rating. ]Nissan Leaf 2012 with new battery May 2019.
5650 W solar, 2xPIP-4048MS inverters, 16 kWh battery.
1.4 kW solar with 1.2 kW Latronics inverter and FIT.
160 W solar, 2.5 kWh 24 V battery for lights.
Patching PIP-4048/5048 inverter-chargers.
