The 60v Discussion

Rules Talk
#1

This is a place for the discussion of the 60v rule. The only way we’re doing this is if we can do it safetly and within specifications of the fuses.

Our current BF1 fuses will run up to 58v nomianal
13s (54.6v, fully charged) still fits within the limits
14s, fully charged at 58.8v would be within the “close enough” range, but the lowest fuse amperage in the series is 30A… at that, we’re 22% higher than the “1440w” target.

“60v” scooter battery, fully charged at 16s is 67.2v… meaning that even its nomininal voltage of 60.8v, we’d need to find a ~23A fuse that will handle the fully charged voltages.

Fuse requirements, if you find something for 60v series…

  • Must be bolt-down configuration, no blade-fuse types (ATO Style). Ideally, would fit in current holders.
  • Must be of a similar trip-curve to the BF1 or the MIDI series fuses we have now.
  • Needs to be cheap.
  • If your team is planning to run one, you must provide spares to the race officials before the weekend begins.

Mike’s hot take time

Another option I’d consider (with the remainder of the PRS board agreeing to it) is bumping up 14s to the 30A fuse, and basing all new fuse ratings on that, since there are so few people running non-lithium chemistries now, it may make the most sense to get everyone on the BF1 fuse.

This would put all karts at ~1600w limits using nominal voltages, a roughly 15% increse in overall power.

End hot take

Please discuss below. I want to close this in no more than 1 week’s time, so next monday, 2023-04-10 is your last day to comment/discuss. Thanks for all your input!

#2

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#3

I made a spreadsheet a while back that I expanded to include 60v fuses and system powers.

Assuming a 3.6v nominal cell voltage. 3.6v@10s, 40A gives 1440w of continuous power.

16s @25A gives 1440w cont power.
17s @23a gives 1400w cont power. (23a is the only low amperage available from littlefuse in the midi format)

I want to compare the powers of the fuse i^2t given a 5s pulse of power or such. and maybe find a 25a fuse we can allow for actual 16s batteries as 16s is the most common “60v” battery.

But with a 23A fuse, we could allow up to 17s, which is 61.2v nominal. The only issue is that the 23a fuse is only rated for 32v. but given we are using it as a power limiter and not really a safety device, I don’t have too many issues with using the lower voltage fuse that would have significant safety margin anyways.

#4

I would maybe suggest this fuse for 16s, 60v, 25a.

it is not the midi style, but is probably harder to get heat out of, and has an i^2t of 3220, which puts it at 7300 joules with a 5s max current pulse. with 48v@30a being 7500j and 36v@40a being 8000j

This fuse would be good for 17s, 60v, 23a.

digikey says it has an i2t of 1400. which puts it at 5100 joules with a max current 5s pulse. significantly below the pulse power output of other fuses. But I can’t find where digikey got this data. They may be wrong.

#5

Both of those fuses are only rated for 32v DC, so they’re a no-go at 60v. The BF1 variety comes in a 58v version as well, which is what we’re using currently for the higher voltages.

#6

I addressed the 32v concern. this is a performance limiting device. not a safety device. you really have to go to different fuse body styles to get higher voltages. The midi style seems to bottom out at 30a with the 23a one not even present in the datasheet for the midi fuse series.
also, fuses are over designed so this should have enough safety factor at higher voltages.

when it breaks; even if a plasma arc is sustained, the motor controller gets an under-voltage and shuts off.

I can blow up a few at 60v to see what happens.

i did look again and found this 58v, 25a fuse that has a similar time to arc vs current curve as the 30a midi.

#7

This is both a safety device and a current limiting device. The BF1 58v fuses are what we’re currently running for most classes.

The fuse you found last is intriguing, but still only 58v. not 60v+ like is required.

Just because something you test “works” doesn’t make it safe.

#8

Truthfully I don’t really get it.

But as long as someone sets the 60v tier to 16s and <=24A, and the overload curve in joules is the same or lower than all the existing ones then it’s fine by me. I do think that the fuse must have the proper voltage rating. I can’t imagine the series actively officially condoning a safety device being operated beyond its ratings.

And I do not agree with having the 48v tier be 14s (e.g. increasing overall wattage output). Don’t get me wrong I would immediately tweak my packs to run at 14s / 30A fuse but that seems like the wrong direction. We will be adding more speed to the field (called “speed creep” in racing circles) which will make it even harder for beginners and will upset those that already have their stuff dialed in and competitive and don’t want to be forced to do something to keep up with the Jones’

#9

58v is close enough to 60V to work fine. there is enough of a safety margin to extinguish the arc.

16s@4.2v is 67.2v fully charged. (12% over voltage)

10S 36v is 42v fully charged and we use a 32v fuse on that. (30% over voltage)

So I propose that we allow the PN 0895025.Z fuse (58v, 25A) with up to 16s lithium ion batteries.

#10

I think that the voltage limits should stay < 50Vs. OSHA considers all voltages greater than 50V to be hazardous and need guarding. See Guarding requirements for 50 volts or more DC. | Occupational Safety and Health Administration

Keeping below this limit is an easy way of showing why the decision was made.

Additionally, I also do no support increasing the fuse rating for 14s. This will increase speed and also increase the amount of batteries that will need to be purchased increasing the barrier to entry. If anything I would say we should decrease fuse limits/wattage allowed.

2 Likes
#11

I am going to stay out of the decision of whether it is even a good idea to allow voltages above “48V”, but here is some stuff I had found following a prior 60V debate:

  • The 25A 80V Littelfuse FKS-ATO fuse would blow much faster at a given percentage of its rating than the MIDI or BF1 fuses (based on I^2*t rating and curves at 2x and 3x rating). I would be 100% confident that this would not give a performance advantage over lower-voltage systems even though it is rated 25A and not 24A.
  • I do not recommend the 25A 58V Littelfuse JCASE fuse. It should blow faster than MIDI and BF1 based on I^2*t rating but its current-time curve shows it being identical to BF1 at 2x and 3x rating. This means that the available 25A fuse @60V would give performance advantage over lower-voltage systems.
  • The 30A 58V Littelfuse MAXI fuse has a lower I^2*t rating than the 30A 58V BF1. This should imply that the 25A version would also be suitable even though 60V technically requires a 24A fuse. This series does not have current-time curves in its datasheet so I can’t guarantee that it would be a fair option.
#12

As far as fuse voltage rating, it will not impact whether the fuse will interrupt current (at least at the voltages we are working with). However, exceeding the fuse’s rating could make it take some milliseconds longer to interrupt current after the element has melted and add a slight chance that the fuse housing may melt or explode when it blows (also low chance at these voltages).

#13

TL;DR: My suggestion would be anything under 60VDC (DC specifically) be considered safe for the series and be allowed with fuses that are rated for 58V, which would allow 14S setups. Additionally, there’s a decent argument from international safety law and standards that voltages ABOVE 60VDC but BELOW 120VDC could maybe be allowed in the future but only with a fast blow fuse, not slow blow.

Hey guys. Coming into this discussion late, but I’m gonna try to catch up.

In the interest of full disclosure: I generally think voltages up to 72V don’t constitute a realistic risk to the series. Also, a fuse is only as good as its placement in the electrical system, so there’s no replacement for SERIOUS, THOROUGH technical inspection at every event. My biggest safety concerns in the past had nothing to do with voltage and everything to do with anything BUT voltage.

  1. “within specifications of the fuses.”

a. How picky are we going to be? Is this a common sense regulation or a liability one?

b. Is 58.8V close enough to 58V? If this is a liability rule, then no. However, I think it is certainly reasonable to allow anything <60V to be run on the 58V fuse.

c. Also, even if you were going to have 58V be a HARD cutoff, that doesn’t mean you need to ban 14S setups. A 14S setup could be made conforming by, say, tweaking the adjustable voltage on a charger to not charge the battery above 58V, giving you 95% charge. I just want to point out that even being hard ass about safety and/or rules still means you should allow loopholes that make sense, which in this specific case wouldn’t be disallowing 14S but instead disallowing voltages under 58V, right?

  1. Assuming the perfect fuse exists for whatever limit we end up wanting to apply, the remaining question is: what voltage limit should really be the upper limit?

a. OSHA has been hassled for their 50V ruling for a long time. It was designed to protect phone line transmission voltage. However, there’s at least SOME legal precedent that for DC voltages specifically, 48V NOMINAL is the intent, meaning that a 48VDC forklift on lead acid chemistry is NOT a high voltage device since the majority of its service life falls below 50V.

b. Most other European, Australian, and Asian agencies use a higher voltage limit for DC than AC, particularly if the voltage source is “current limited”, which for us means fused.

c. Example for B: IEC, an international organization, defines “EXTRA LOW VOLTAGE” or ELV as “DC voltage that does not exceed 60V” but does not require a current interrupter. Also, it defines “hazardous voltage” as “any voltage exceeding 60VDC without a limited current circuit”, but the next tier of their ruleset starts at 120VDC. So, within that context, as long as a 200ms fuse is specified that DC voltages OVER 60VDC but UNDER 120VDC are not considered hazardous and could be considered as a possibility for PRS in the future, though I don’t think there would be much desire for that.

#14

As far as pickiness, this is more of a common sense regulation. Most of the debate is in trying to balance ability to use readily available higher-voltage scooter/moped/power equipment motors with practical safety given that a lot of PRS vehicles are built and wired in very sketchy fashions.

#15

The power/fuse limit is partially for liability reasons.
I do miss the good old days of putting forklift motors in powerwheels cars though :slight_smile: