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Old 05-22-2019, 12:42 PM   #1 (permalink)
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Default Bigger IMA fuses for Current Hacks..

As we know the Insight G1 uses a standard Littelfuse L50S semiconductor series 100A rated fuse.
This is ok for 99.9% of the time in a standard system, but can fail due to age, fatigue etc leading to strange P1576 errors.

For those looking ahead at Lithium with current hacks etc, the 100A fuse won't stand it for long without leaving you stranded.
The L50S series is also available in 125, 150, 175 & 200A rated versions.
I have used at least three of those in my various projects and Lithium packs over the years.

I would suggest a minimum 150A rated fuse should be used when using the +30% current hack.
These bigger L50S fuses will fit the IMA switch board with a little dremel work or pliers to relieve the fuse surrounding plastic..

They aren't cheap new, so keep your eye out for them on e-bay/etc.

This might be of interest to a US based buyer (group buy) 5x 200A versions.

https://www.ebay.co.uk/itm/Littelfus...A/253109830498
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Old 05-22-2019, 11:26 PM   #2 (permalink)
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Fair warning to those who might consider using a cheaper fuse: DON'T!

DC bus fuses are designed to safely & successfully open when placed under tremendous DC overcurrent conditions. DC is really hard to safely fuse because the voltage waveform has no zero crossings; once an arc forms in a DC fuse failure condition, said arc will persist until the air breakdown gap gets large enough. A general rule is that a fuse's DC interrupt current is five times less than its AC rating (e.g. a fuse with a 200 amp AC interrupt rating is only rated to 40 amps DC).

When a fuse initially begins to open, the current through it is extremely high, but since there's very little forward voltage drop, the fuse initially actually consumes very little power. However, as the fuse element begins to vaporize, the forward voltage rapidly increases, whereas the forward current only drops slightly. Thus, the fuse consumes the most power immediately before it opens (when the interrupt current is still large AND the voltage across the element is large (but has not yet opened)). The disintegrating body needs to be able to safely absorb this power while the fuse is failing... a fuse that isn't rated to the system voltage won't be able to handle said power, and could continue to fail short long enough to start a thermal event (i.e. a fire). To prevent said fire, high voltage, high current fuses typically use a sand-based energy diffuser; when these fuses fail, their insides absorb so much energy that the sand usually turns into glass!

Note that a fuse's rated breaking current capacity needs to be MUCH MUCH larger than the fuse's rated "continuous" rating... short circuiting a lithium stack generates thousands of amps... for example, shorting a 200 volt lithium stack with 4 gauge leads 1 meter long will theoretically generate about 8,000 amps for a brief instant. In reality, the stack voltage will majorly sag, such that you might 'only' see 3,000 amps or so, which is still a lot. Consider that the fuse needs to absorb that current while simultaneously developing the entire pack voltage across it... even if the peak current lasts for just 2 ms, the fuse will need to absorb 3,200 joules.... that's the same amount of energy required to heat an ounce of water 33 degrees celcius, only it's consumed in just a blink of an eye.

Taking this one step further, considering an OEM NiMH pack in excellent condition has terribly high ESR (400 mOhm or so), whereas lithium packs are at least an order of magnitude smaller (well under 1 mOhm/cell), we need to make sure the OEM fuse can handle the increased peak breaking current. Fortunately, the OEM fuse can withstand 20,000 ADC in a fault condition... once again, Honda WAY over-designed the IMA system (or less likely, their design was forward-looking to lithium in the future). So we can safely use the OEM fuse with lithium setups... yay!

A fuse will typically last for 100 hours at its specified 'continuous' current rating. This time-current constant is inversely logarithmic, which means the fuse will fail much faster for each incremental current increase (e.g. at 110% of specified current, the fuse might fail after just 4 hours, and at 120% it might fail in 100 seconds, and at 150% it might fail in 10 seconds, etc). So in short, you'll want the peak current pushed through the IMA's DC bus to always stay below ~110% of the rated fuse values. Above 110%, the fuse will fail very quickly, as explained above.

Note that ganging fuses in parallel in an attempt to increase the continuous current rating doesn't work well in practice... although I often see parallel fuse implementations in shipping products, this isn't recommended due to the positive ESR increase as load current through any single fuse increases... thermal runaway at its finest. Don't do it.

At the end of the day, fuses are just an engineered copper strip that has very repeatable failure modes... and those modes are cumulative, based on all prior current that previously travelled through said copper (particularly overcurrent events). Keep this in mind before considering buying used fuses... just like a battery, all fuses have a useful life.

In short, please Please PLEASE don't use any fuse that isn't specifically designed to handle the full open circuit DC voltage AND the rated continuous current AND the interrupt rating.

/soapbox

...

SO with that background out of the way, let's look for some (potentially) cheaper fuses. Thanks to the EV & PV industries, we can probably find a cheaper substitute. Littelfuse is the best in this industry, so let's start there.

For $53, their L17T200 fuse is rated to 200 A and has a 170 VDC break voltage. This same series goes all the way up to 1200 amps, so they're got us covered! Alas, the 170 VDC break voltage isn't as high as we'd like... the G1 can OEM handle up to ~210* volts before the DCDC shuts down (*correct me if I'm wrong).

For $52, their JLLS200.X fuse is rated to 200 A and has a 300 VDC break voltage. Now we're talking. The DC interrupt current rating is 20,000 amps (same as OEM), which is good for all lithium stack ESRs I know of (for now). The bolt-to-bolt spacing is 63.7 mm C2C... OAL is 82.6 mm. Peter, will it fit?
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Old 05-23-2019, 01:38 AM   #3 (permalink)
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Mudders warning is correct. Use a correctly specified DC capable one..

Difficult to get cheaper correct OEM series fuses than the 5 x 200A fuses in the e-bay auction. $20 each maybe..

I would have bought them if they were in the UK..
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Old 06-11-2019, 05:34 PM   #4 (permalink)
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Was there any positive outcome in finding stock or near stock size fuses with higher amp ratings. Im about to the point to increase fuse size for the current hack That and i blew my stock fuse when alligator clip popped off while i was checking voltges at my bcm fooler.
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Old 06-11-2019, 05:47 PM   #5 (permalink)
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e-bay or buy them new.. L50S there are loads.
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Last edited by retepsnikrep; 06-11-2019 at 05:49 PM.
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Old 06-11-2019, 11:02 PM   #6 (permalink)
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Is $10 for a L50S 200A a good deal?

Also is there a way to test these to make sure they aren't faulty or damaged?
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Old 06-11-2019, 11:08 PM   #7 (permalink)
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Quote:
Originally Posted by Sigma Projects View Post
Is $10 for a L50S 200A a good deal?

Also is there a way to test these to make sure they aren't faulty or damaged?
The only way to fully 'test' them is to blow them out with a precise current, then make sure the fail time matches the stated specifications. Obviously you don't want to do this destructive test, but this is how fuse manufacturers verify each fuse lot (i.e. blowing out a few fuses from each batch).
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Old 06-11-2019, 11:42 PM   #8 (permalink)
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Quote:
Originally Posted by mudder View Post
The only way to fully 'test' them is to blow them out with a precise current, then make sure the fail time matches the stated specifications. Obviously you don't want to do this destructive test, but this is how fuse manufacturers verify each fuse lot (i.e. blowing out a few fuses from each batch).
Understood. What do you think the risk of running an older L50S 200A would be? Would it not blow at the rated specs? Or would it just blow sooner?
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Old 06-12-2019, 12:48 AM   #9 (permalink)
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Old fuses that were initially 'good' will ONLY blow out sooner as time goes on.
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Old 06-12-2019, 01:08 AM   #10 (permalink)
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Quote:
Originally Posted by mudder View Post
Old fuses that were initially 'good' will ONLY blow out sooner as time goes on.
Ah ok great, thank you.
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