What about setting up a bank of oven heating elements? They seem to be around 2.5kW, and you could probably air cool 20 of them for a short amount of time. They’d probably even be able to dissipate 80kW for a very short time, probably.
50 kW from a 300 Volts battery…
That’s 166.667 Amperes through a load resistance of 1.8 Ohms.
So you basically need a temperature stable 1.8 Ohm resistor capable of dissipating 50kW of heat.
Oof…
You’ll basically need a lot of constantan wire.
Not too thick so you can cool it better.
Probably a bunch of lengths in parallel.
You’ll have to put it in running water of enough liters a minute.
Maybe from a tap, so you don’t have to cool it, just lose it in a drain.
I don’t know if there are fire hoses where you want to do this, but that’ll give you enough water per minute for sure.
Put the connections as far apart as possible to avoid electrolyses.
Do the test outdoors.
Metal garbage-can filled with crushed charcoal briquettes, big honkin’ piece of rebar driven down the middle (NOT touching the bottom of the can!), and you got yourself an industrial-strength carbon-pile.
Adjust volume and packing to get the resistance you want.
When I was in the Navy we had a dummy load to test our transmitters power, and to electronically tune antennas before applying transmission power to the antenna. If not tuned properly you can blow your amplifier, transmitter and everything connecting the transmitter to the antenna. The transmitters started at 1kW up to 5kW. The dummy load was basically a huge resistor in a protective box and the entire unit weighed in at around 400 pounds. This was the gear on a submarine, so I’m sure shore based transmitters that were much more powerful, up to 100kW or more, their dummy loads were massive. I can’t remember the exact technical specs on it because this was back in 1985 I worked in communications for the Navy. I’m sure technology has reduced the size of resistors used for dummy load but it will end up being something very solid and heavy for testing 50kW. Keep us posted, I would really like to see what you guys come up with.
50kw is small car motor power.
Look how does car power tests stands look like.
In general, there are two main ways - use big heavy drums that are hard to increase rpm (for short-tests), and same with extra brake load (machanical/electrical, extra water cooling is required!).
Do you have motor that you are going to feed with this pack? Otherwise, you will need lots of money to simulate same current…
Use 9 of them in a series parallel configuration and fill them with water. Surprisingly perhaps to some, the specific heat of water is 10 times that of copper. I haven’t done the calculation but I don’t think you would even need to circulate the water.
240V water heaters would be overdriven at 300V DC. Are you able to throttle the output of the pack?
EDIT:
If I assume those 720 cells are 3Ah each then
a single 60 Gallon water heater can absorb the 28 million Joules of energy, raising the water temperature by about 30 degrees Centigrade
Water cooled for 50KW? Large fans will cool a resistive loadbank that size no problem. Your looking at a loadbank probably the size of a small chest freezer, fairly easy two man lift also for loading etc.
I regularly use 500KW loadbanks, sometimes into the MWs and all are force air cooled.
This is not going to be as hard as some think!
If you figure each of the 720 cells are 3Ah each, then we are only talking about 720 x 3.6V x 3.0Ah = 7776Watt-hours
or 7.776KWh
At a 50KWh rate discharge, it will only need to run for about 10 minutes.
No need to circulate water etc. It is not THAT much energy.
Many of the above suggestions sound quite viable but I think the thing we may need to know is the approximate budget for this project. That will determine where it will fall on the janky vs nice scale. The water heaters could be reasonable if you can find some used but the elements are quite cheap so if you just put some of them in a cheaper container. Something air cooled may be more portable if that’s useful but that will increase the cost quite a bit. Also depends how stable you need the load to be, doesn’t sound like it’s that important for this application.
While I’m guessing you have the budget for the water heater elements if you want something cheaper my suggestion would be some steel cable in a some water, or just pass the power directly though the water, you can adjust the power but changing the electrode area in contact with the water or adding salt. This is often used in things like DIY ARC welders and really unsafe home appliances.
The Opie didn’t say how the cells were configured, but i’m guessing 90s8p to get a nominal 300 V pack. (270 to 378, low to high)
So 50,000 W from 300 V would be about 167 amps or 21 Amps per cell. At the peak of 80 kW it would be 267 A or 33 Amps per cell.
That’s quite sporty for 18650—does the pack have cell-level fuses, temperature sensors and cooling, plus active control to pull back the current if redlines are exceeded? If not then be very careful about when, where and what you are doing—that is not a trivial pack to be riding cowboy, might go thermal on you and create a b0mb.
