Amp draw for short bursts versus long duration......

[recumpence]

Hey Guys,

Those who know me know that I pull huge amps through my systems. It is not uncommon for me to pull upwards of 260 amps (I have seen 320 amps on occasion with one motor and 600 amps with twin motors) in tiny bursts numerous times during a typical ride. I have never had any issues with batteries, wiring, motors, etc doing this. However, I recently had some experience with high amperage that I wanted to share with you.....

I have a client who apporached me with an OEM marine project. I cannot give you specifics on components, but I want to share the current draw issues I encountered;

I setup the system with a 12S-24ah Nono-tech pack. The packs all fed a common buss that fed power through 2 gauge (HUGE) fine strand power wire into the 8 gauge controller wires. The controller wires were dry crimped, then soldered to the 2 gauge main power wires. The three motor wires (8 gauge) were connected to the controller using 6.5mm bullet connectors.

The system draws 220 amps continuous. After 7 minutes at 220 amps, all of the wiring burned completely. The 6.5mm bullets melted, the 8 guage wires melted together, the 2 guage wire was too hot to touch, the controller finally smoked and the motor windings were melted. This was all despite the motor being fan cooled through the windings and liquid cooled around the housing. The next setup eliminated all bullet connectors and the wires were doubled up and bolted together. The wiring was shortened and a new (bigger) controller was installed along with a more appropriate KV motor. This time the exact same thing happened. At this point, the only solution I can come up with is twin fan and liquid cooled motors, twin liquid cooled controllers, solid brass buss bars and 0 gauge wire.

Moral of the story; high [true] continuous current is extremely difficult to control. In fact, the wire diameter was such that wire weight became a real concern. The project had over 4 pounds of wire in a very small compartment just due to the huge gauge that was being used.

I bring this up because the higher powered systems I have built typically only use 8 guage wire (if the runs are short enough). But, no more than about 3,000 watts (70 amps) is pulled for more than a second at a time. The huge 200 to 300 amp draws are in bursts of less than 1 second duration.

Just an interesting case study I felt you guys would enjoy hearing about.

Matt

 

[nutnspecial]

Very cool. For stuff like that it seems a completely different method is called for?
Like solid, and closer, power routes from battery>controller>motor?
Highly purposed, custom, no modular wiring etc?

 

[recumpence]

Very cool. For stuff like that it seems a completely different method is called for?
Like solid, and closer, power routes from battery>controller>motor?
Highly purposed, custom, no modular wiring etc?

Pretty much

 

[Punx0r]

RC ratings meet the real world...

 

[ferret]

Very cool. For stuff like that it seems a completely different method is called for?
Like solid, and closer, power routes from battery>controller>motor?
Highly purposed, custom, no modular wiring etc?

Actually, very hot :wink:

An easier solution is to switch to higher voltage to reduce the current (for the same power).

 

[recumpence]

Very cool. For stuff like that it seems a completely different method is called for?
Like solid, and closer, power routes from battery>controller>motor?
Highly purposed, custom, no modular wiring etc?

Actually, very hot :wink:

An easier solution is to switch to higher voltage to reduce the current (for the same power).

Not a workable solution for something being ridden by a person in the water. 50 volts is the maximum safe DC voltage for possible human contact.

 

[macribs]

If you already are diving into water cooling, why not cool the wires/bus bar as well with water? If water cooling still gives you headache you should consider a faster pump, bigger reservoir or better thermal exchange/heat sinks.

Not a workable solution for something being ridden by a person in the water. 50 volts is the maximum safe DC voltage for possible human contact

So will you show us a little something about this "water toy"? I am guessing a water jet electric wake board? And I would love to read more about it, see pics and hopefully see some videos of it.

 

[liveforphysics]

Sounds to me like controller shoot-through happened.

If a harness fails in a given spot it's likely to be slow thermal climb. If a harness fails everywhere at once, this often means FETs stayed latched on somehow to dump the pack into the motor and harness in a short period.

 

[nutnspecial]

Doesn't home 200a service use 4/0 <aluminum> gauging? NEC specifies any connectors as weak links for non service application, and 2 ga copper as a minimum for 100a, iirc. Could have been a controller breakdown too, but that's an odd one if so.

 

[liveforphysics]

Doesn't home 200a service use 4/0 <aluminum> gauging? NEC specifies any connectors as weak links for non service application, and 2 ga copper as a minimum for 100a, iirc. Could have been a controller breakdown too, but that's an odd one if so.

It can be ESC from multiple types of glitches, it can be motor if phase leads chaffed/melted and shorted. If say the motor fails first, it sets forth the cascading series of magic-smoke releases to happen so rapidly afterwards it can look like everything failed simultaneously and can be tricky to troubleshoot.

 

[nutnspecial]

imo sounds like the phase wires were way to small, and at that point the motor itself can become suspect as weak too should the windings then fry first.

I thought I remember you mentioning something about high powered systems tending towards more integrated motor/control for this very reason lfp? And isn't the 2ga for 200+ amps of battery def also undersized? Just 2c.