I am not sure if it will be available in the USA, but, if it is, this Discovery+ documentary is well worth a watch.
All the best,
Paul
Iām going to piggyback on this thread since itās related.
Iām posing this question as a āhypotheticalā discussion only, not official advice.
Suppose I wanted ideas on how to switch a 90V DC battery bank (115V max) that can withstand significant currents. The required Pulsed DC Output would generally be ~60 Hz (not critical) with ~6 ms impulse. The Peak Power Demand is 100 kW , but itās a 36% Duty Cycle.
The transient voltage spikes are what concerns me. Would clamping diodes or a Cap bank be preferred?
To make things even more interesting, this would be used in a saltwater environment - so less sophistication is better (service and parts replacement costs).
Iām aware of the Life-Safety implications and that would be the most important aspect.
Before actually moving forward, I would hire a design professional with relevant experienceā¦but Iām looking to feel a little more comfortable with the direction to take first.
Iām solid on the massive Battery Bank and itās protection. Itās the switching 100 kW DC fast that feels like it will get Loud, Hot, and Violent.
Thanks in Advance,
Ryan
I do not purport to be an expert on solid state devices but my field exposure to big variable frequency drives tells me that job lands squarely within the scope of one or more large IGBT bricks. Those can be found with ratings as high as 2000 amperes at 4500 volts.
Of course, those kinds of ratings donāt exactly come cheapā¦
https://www.digikey.com/en/products/detail/infineon-technologies/FZ2400R17HE4PB9HPSA1/7791987
The second-hand market will be your best bet if this is a personal project. And obviously a bank of rectifier fuses will be an extremely wise investment. Both to protect the IGBT module and the battery.
For that matter if weāre talking about a lithium battery that is good for 100+ kW aboard an oceanic vessel then I would say a fire-rated battery vault protected by a fire pump and deluge-type fire sprinkler system are all but mandatory as well. This is the same type of sprinkler system that is used for the containment of large oil-cooled transformer fires and nitrate cinema film fires. The mode of action for all three fire loads is the same: Spray water on them indefinitely to absorb the incredible heat they give off until they finally burn themselves out many hours later.
Either that or some reliable, fast-acting mechanism with which to simultaneously disconnect and eject a burning battery into the ocean to save the boat & crew. Preferably one that can be operated remotely and/or automatically by action of a pull ring or fusible link, etc.
A lithium battery is an entirely different fire load aboard a boat than something more conventional like a fuel fire. Diesel, gasoline and engine oil can all be reliably extinguished by CO2, multipurpose dry chemical or Halon 1211/1301 (and itās modern replacements) because all of those fuel burdens rely on an interface between themselves and atmospheric oxygen for combustion. Whereas lithium batteries produce their own internal supply of oxygen within enclosed, impenetrable cells to perpetuate their own combustion. This means that conventional fire extinguishing agents cannot get where they are needed in order to be effective against battery fires. Thus the only solution is to simply let them burn inside of a fire-rated containment vessel whilst continuously dousing them with water to absorb the tremendous heat they give off.
And of course there is also the matter of the environmentally persistent heavy metal and organic toxin pollution that is generated by suppressing lithium battery fires with waterā¦
@HeavyIron , Thanks for the reply and especially the link to a specific IGBT module to start studying.
Iām actually surprised that a 1700V 2400A is less than $1k each. That is orders of magnitude cheaper than I was expecting for this application.
You can find similar ones for about half of that on eBay. People like to part out old VFDs and sell the guts as project parts.
One other consideration I would add that ought to be addressed for a project like this is the need for a fire-rated ventilation path & class 1, division 2 explosion-proof exhaust fan in addition to suitable fire / explosion containment. Lithium batteries can produce a lot of explosive gasses when they fail.
This video covers an installation of a scale and chemistry that is likely similar to the one you are contemplating for this project:
The gentleman who made that video has a wealth of other content discussing lithium battery fire safety that I would encourage you to explore.
10-4. Iām good on the LiFePO4 bank and protection. The Fire Safety is the one part thatās in my wheelhouse.
Itās the voodoo magic of switching DC high currents fast that Iām trying to gain some general knowledge ofā¦just to start a preliminary direction.
You may be able to bring project costs down and boost efficiency by raising voltage and reducing current. At only 90 volts DC your forward conduction losses for a ~135 horsepower load will be quite high and your wiring will be very heavy.
You may be able to get by with a commercial 208 volt or 240 volt VFD and a three phase induction motor. That way you can simply pipe your battery voltage into the driveās DC link terminals via some sort of bidirectional DC-DC converter / regulator. Or else a unidirectional converter working in conjunction with a brake resistor.
At a DC link voltage of 330 your amperage will drop to about 300. A single set of 350 kcmils will handle that. Otherwise youāre talking three parallel sets of 500 kcmil copper to handle ~1200 amperes at 90 volts. Very heavy and absurdly expensive.