How to run more current through fuse?

[nbritton]

How about the different fuse types 125A vs 40A. I have a hunch that the 125A is more tolerant to overloading and abuse than the 40A fuse.

No matter which voltage/fuse combination you choose you'd have to overload the fuse by the same % of it's nominal rating to achieve the same % increase in power output. What makes you think that the 125A fuse will be able to tolerate a higher % of it's nominal rating before it pops?

My 2c:
I^2*R losses will be higher in the 125A fuse - think about it, the fusible element is thicker so it's going to take more power (=heat) to blow it, so the I^2*R loss in the 125A fuse has to be worse for the same system power output compared to the lower current fuses.

Therefore if you are overloading the 125A fuse by a given % you generate more excess heat than the same % overload on the 40A fuse. If you consider the fuse holder to also be acting as a heatsink, then it's going to run cooler with the 40A fuse than the 125A, therefore the rating of the 40A is going to be boosted more by the cooling effect of the fuse holder - long term of course, the fuse holder isn't going to help you much for a 10 second overload.

Not only that, but you would need like 0000 AWG wire to manage 167A. With 36V you can use 6 AWG. The rules say you can't spend more than $500 total.

[nbritton]

you can find them for even cheaper, if you had one per tire, then at full throttle you would be just under at 1400W consumption, but throw in a boost converter and you can go way higher for bursts, 48V would get you to about 2500W for however long you where safe to do so, but you can scale that in your controller to prevent instantly popping the fuse,

Per the rules, the voltage at the motor can't be higher than 36V RMS and also there is a $500 budget limit:

2.7 | Motors
All motors must be electrically powered. All power supplies must range from 12-36 volts RMS maximum input to the motors. Before each race, track officials will test the voltage to the motor of each vehicle.

1.4 | Team Budget
The total allowable budget for any individual vehicle is $500 USD. This includes any and all equipment, devices, performance gear, and propulsion materials on your vehicle as it stands on the starting grid. This does not include all the support equipment (spare batteries, team transport, tools, etc). In short, everything that goes into your car must not have costed you more than $500, EXCLUDING the total cost of your batteries, team operations, and most importantly ALL safety equipment. See Section 4, Excluded Team Budget Items, for further clarification of what does NOT count towards the $500 limit.

2.5 | Battery
The PPPRS permits use of the following chemistries:

• SLA (Marine labeled sealed lead acid, Absorbed Glass Mat)
• LiFePO4 (Pre Approved Brands: A123, CALB, & Headway)
• NiCd
• NiMH

LiPo is NOT permitted. All other lithium battery brands not listed here will require approval by the Sanctioning Body. Batteries are worth half their fair market value towards the total of your $500 budget. This represents the batteries that are present in the machine on the race grid. While the spare batteries in the pits are exempt from the overall $500 limit, they will still count in your budget when in use on the track. No single battery pack shall result in pushing the car’s budget above $500.

[SeanB]

72V supply and the fuse on the battery bank, then a buck converter to supply 36.0V to the motor terminals, using sense feedback to the buck converter at the terminals.

[nbritton]

72V supply and the fuse on the battery bank, then a buck converter to supply 36.0V to the motor terminals, using sense feedback to the buck converter at the terminals.

My interpretation of the rules are that the power supply also can't exceed 36V. The wording verbatim is: "All power supplies must range from 12-36 volts RMS maximum input to the motors."

Furthermore it says: "Before each race, track officials will test the voltage to the motor of each vehicle." what test point are they measuring???

[DanielS]

72V supply and the fuse on the battery bank, then a buck converter to supply 36.0V to the motor terminals, using sense feedback to the buck converter at the terminals.

On top of the 36V maximum voltage in the rules, you have the 1440W limit from the battery and I bet the safety rules also prohibit running fuses beyond their nominal breaking voltage.

So you would get disqualified for obviously intending to draw twice as much battery power than permitted, exceeding the voltage rating of provided fuses and exceeding the maximum voltage rating allowed on the track.

The reason for 36V as the limit is likely to practically eliminate electrocution hazards, so I doubt anything higher at any point in the drive train and support systems will be tolerated.

[NotABagel]

72V supply and the fuse on the battery bank, then a buck converter to supply 36.0V to the motor terminals, using sense feedback to the buck converter at the terminals.

My interpretation of the rules are that the power supply also can't exceed 36V. The wording verbatim is: "All power supplies must range from 12-36 volts RMS maximum input to the motors."

Furthermore it says: "Before each race, track officials will test the voltage to the motor of each vehicle." what test point are they measuring???

This correct.  The rules around voltage requirements are pretty strict, and they look at the motor terminals for voltage.  Most other teams were simply pushing extra current through their fuses in bursts, but I want to go further.

[Fungus]

72V supply and the fuse on the battery bank, then a buck converter to supply 36.0V to the motor terminals, using sense feedback to the buck converter at the terminals.

Do you think they'd hand out a fuse without measuring anything? In that case everybody would just ask for the 125 amp fuse.

[Mechatrommer]

Thanks for the suggestions, though here's the thing:  I don't want to cheat.  The rules for the race permit you to run what you can through the fuse they supply.  If you change the voltage, that's not allowed.  If you swap out the fuse you are given, that's also not allowed.  If you can figure out how to trick the fuse, that's lauded.

design a fuse holder in practical sized watertight box enclosure. you have sealed door for easy fuse replacement. put water in it...your fuse will become a nice water heater for the duration of your racing... you can make a "digikey fuse flavored" coffee then to enjoy the winning... edit: ps: dont forget the pressure relieve valve you dont wanna blow your fuse holder due to excessive steam pressure... ymmv..

[TheRevva]

I only read a couple of pages of this thread, and I have to admit that it was all 'intriguing' to say the least...
Many of the comments dealt with various methods to keep the fuse from getting hot enough to actually melt.
Immersion in liquid nitrogen was one, fairly logical, method to keep things nice and cool....

However...
Is there any aspect of the rules that state you're not allowed to 'immerse' the entire fuse (holder and all) into a nice bath of ... say... good old LEAD.
Imagine a small pot / kettle full of molten lead.  The race inspector first 'verifies' that you have the 'correct' fuse and possibly even the correct fuse holder too.  Once it has 'passed' that inspection, you immerse the ENTIRE fuse + holder into the bath of molten lead (making sure the molten lead forms a nice connection to BOTH sides of the fuse).  You wouldn't even need to retain the lead in a molten state... (In fact, it'd possibly be wise to HELP it solidify)
It'd probably qualify for the "I am not mad but..." clause, and I'm pretty confident that with a large enough 'bath' of lead that just happens to be in direct contact with BOTH of the fuse connections, the fuse would be fairly unlikely to blow... Hell, even if it DID manage to melt the fuse, the surrounding 'lead bath' would still happily allow a few THOUSAND Amps!!! <Grins>
(I'd strongly recommend installing an 'additional' fuse of appropriate rating for basic safety though).

Then there's the next suggestion....
Does it actually SAY in the rules that you cannot connect both the SUPPLY feed _AND_ the load from the motor onto the SAME side of the fuse?  (i.e. The fuse is actually NOT pat of the circuit)
In that case, I would SERIOUSLY doubt the fuse would blow even if you were drawing several MEGA AMPS.  (If the fuse DOES somehow manage to go open circuit though, you'd have some SERIOUS issues and might require the fire department rather urgently)

[Fungus]

Thanks for the suggestions, though here's the thing:  I don't want to cheat.  The rules for the race permit you to run what you can through the fuse they supply.  If you change the voltage, that's not allowed.  If you swap out the fuse you are given, that's also not allowed.  If you can figure out how to trick the fuse, that's lauded.

design a fuse holder in practical sized watertight box enclosure. you have sealed door for easy fuse replacement. put water in it...your fuse will become a nice water heater for the duration of your racing... you can make a "digikey fuse flavored" coffee then to enjoy the winning... edit: ps: dont forget the pressure relieve valve you dont wanna blow your fuse holder due to excessive steam pressure... ymmv..

Really? You'd base your chance of race success on something as random as that?

[Fungus]

I only read a couple of pages of this thread, and I have to admit that it was all 'intriguing' to say the least...
Many of the comments dealt with various methods to keep the fuse from getting hot enough to actually melt.
Immersion in liquid nitrogen was one, fairly logical, method to keep things nice and cool....

They banned capacitor banks on safety grounds so it's a safe bet they wouldn't allow that.

However...
Is there any aspect of the rules that state you're not allowed to 'immerse' the entire fuse (holder and all) into a nice bath of ... say... good old LEAD.
Imagine a small pot / kettle full of molten lead.  The race inspector first 'verifies' that you have the 'correct' fuse and possibly even the correct fuse holder too.  Once it has 'passed' that inspection, you immerse the ENTIRE fuse + holder into the bath of molten lead (making sure the molten lead forms a nice connection to BOTH sides of the fuse).

How is that different from just soldering a wire across the fuse holder? Do you really think they'd allow that?

Then there's the next suggestion....
Does it actually SAY in the rules that you cannot connect both the SUPPLY feed _AND_ the load from the motor onto the SAME side of the fuse?  (i.e. The fuse is actually NOT pat of the circuit)
In that case, I would SERIOUSLY doubt the fuse would blow even if you were drawing several MEGA AMPS.  (If the fuse DOES somehow manage to go open circuit though, you'd have some SERIOUS issues and might require the fire department rather urgently)

Really?

[DanielS]

Does it actually SAY in the rules that you cannot connect both the SUPPLY feed _AND_ the load from the motor onto the SAME side of the fuse?

The rules would not require the use of official-provided fuses if they could so casually be bypassed. There is no point in specifying a fuse if it is not required to be in-circuit where it is intended to be: between the source and whatever is connected downstream.

[Kalvin]

Energy density 12V battery vs 36V battery. How large a volume is needed for the battery/batteries? Those cars are pretty small. What is the total energy required during the race?

There are 1500W 12V DC/AC inverters available, compact in size too. Maybe a 12V DC/DC-converter driving the motor(s) would be okay too. I am not sure about the I2R losses here if the converter is placed close to the battery. And there is still current advantage for the 12V over other voltages, should there be higher power loss using 12V power supply and which may compensate the losses. And, if the 125A fuse is more tolerant to overload, this could provide some opportunities.

[Mechatrommer]

Really? You'd base your chance of race success on something as random as that?

no its not random, its thermodynamics law and used in millions of kettle, unless you take it for granted without proper testing and math. my uneducated guess, you can double your system wattage with this method. anyway, its your choice on more advanced technological features that maybe cost weight and money and err reliability (read as randomness or murphy's law)... this is "hack" thread afterall. i was about to give another nasty but better non random hack but its strictly speaking illegal if found out by the organizer. learnt from the ghetto..

[Fungus]

Really? You'd base your chance of race success on something as random as that?

no its not random, its thermodynamics law and used in millions of kettle

a) Kettle elements aren't made of stuff which is near melting point at 100 degrees C. Small hotspots are OK.
b) Kettles aren't bashed around much.

[Mechatrommer]

a) Kettle elements aren't made of stuff which is near melting point at 100 degrees C. Small hotspots are OK.

so does fuse element. except kettle element will take all the power when energized. whereas fuse element only take excessive wattage when you start beyond the rated wattage. meaning while you are under the specifed 1440W, there is no heating going on, no coffee for you

b) Kettles aren't bashed around much.

thats why the watertight and pressure relieve valve suggestion. the OP's job is to ensure 2 things though that i dont need to feed:
1) the fuse is immersed in water all the time, that probably means near full water before closing down the fuse holder door.
2) the water can get into the fuse enclosure into the fuse element... suggesting an assumption that the "organizer's approved fuse" is not watertight. well YMMV...
and 3) its the OP's job to make the whole water heater thing is bash proof...

edit: water heater thing in automobile have been around for decades, its called radiator... YMMV..

[Ian.M]

From a safety viewpoint, I cant see the judges permitting a fuse cooling system that could discharge steam or boiling water.   I thought I was pushing it to suggest a fully sealed Fluorinert heat-pipe system, which would have to be very carefully engineered not to discharge coolant. 

Also, once you get high enough temperatures at the surface of the fuse's internal element, any leakage into the fuse body will result in a tiny amount of water flashing to steam which will blow the s--t out of the fuse, rupturing the body and severely stressing the element.   You really don't want a cooling system that vastly increases the probability of fuse failure when you hit the throttle several corners intop the race!

[langwadt]

72V supply and the fuse on the battery bank, then a buck converter to supply 36.0V to the motor terminals, using sense feedback to the buck converter at the terminals.

My interpretation of the rules are that the power supply also can't exceed 36V. The wording verbatim is: "All power supplies must range from 12-36 volts RMS maximum input to the motors."

Furthermore it says: "Before each race, track officials will test the voltage to the motor of each vehicle." what test point are they measuring???

This correct.  The rules around voltage requirements are pretty strict, and they look at the motor terminals for voltage.  Most other teams were simply pushing extra current through their fuses in bursts, but I want to go further.

if you are not allowed any storage after the fuse there isn't much to gain other than trying to get as close to blowing as possible.

I imagine measuring the current through and voltage across the fuse to calculate the resistance and thus the temperature.
Then have the motor controller pull as much current as needed while keeping the fuse wire temperature below some safe level

[Mechatrommer]

From a safety viewpoint, I cant see the judges permitting a fuse cooling system that could discharge steam or boiling water. I thought I was pushing it to suggest a fully sealed Fluorinert heat-pipe system, which would have to be very carefully engineered not to discharge coolant.

point the steam relieve valve drain downward to the road? i'm pretty sure the fuse compartment is somewhere far away from the driver's seat regardless of where you point the drain, heat from the motor should be more of the concern, no?. then whats the contigency plan if indeed through murphy's law, the fuse blows up from inside during the race? i dont see much difference in safety point of view to the "harmful if inhaled, and care should be  taken to avoid contact with eyes and skin" Fluorinert https://en.wikipedia.org/wiki/Fluorinert how about lets push it further... a very carefully engineered and sized sealed container not to discharge steam? perharps an aluminium sealed box with fins and door and a body temperature controlled 12W fan? 5mm aluminium thickness and M16 bolt nut door retainer should be more than safe enough in case steam do indeed develops from inside.. edit: whatever the system will be like, i hope that can fit in the $500 budget..

[Fungus]

if you are not allowed any storage after the fuse...

It doesn't say that, it just says "no capacitor banks".

point the steam relieve valve drain downward to the road?

What would it get you? 5% extra? Just build a better car, it will be easier.

[langwadt]

if you are not allowed any storage after the fuse...

It doesn't say that, it just says "no capacitor banks".

there is not a lot of other ways to store a appreciable amount of electric energy

[Fungus]

there is not a lot of other ways to store a appreciable amount of electric energy

There's not a lot of ways to cheat a fuse either.

I say keep it simple: Put in a fuse temperature sensor and a MOSFET. Apply PWM if the fuse is getting too hot.

An inductor to smooth the PWM plus current sensor would help too - that way you're not relying on the motor to keep the fuse alive.

[AMS]

How about using a peltier cell to cool the fuse done when needed. You can control it via micro controller or even a simple threshold switch circuit. I have used peltier cells before to cool stuff down and it certainly works very well all you need is the cell, supply, heat sink and potentially a fan (on the heatsink).

[Fungus]

How about using a peltier cell to cool the fuse done when needed.

They need a lot of amps...   

(but I guess you could cool a big chunk of metal when you're braking and the amps aren't needed for the motor...)

[AMS]

How about using a peltier cell to cool the fuse done when needed.

They need a lot of amps...   

(but I guess you could cool a big chunk of metal when you're braking and the amps aren't needed for the motor...)

Exactly, he cannot store charge in capacitors but I assume there is no ban on storing thermal energy (or in this case lack of thermal energy). when the motor is under the max allowed current the rest can be used to cool stuff (sealed cooling system or simply as you pointed out a chunk of metal).