UK Kilobots - 1.362kg (3 lbs) Combat Robots

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Originally Posted by mr_turbulence

The fuse is to protect your robot from pulling more current then the maximum discharge rate of the lipo. Over discharging a lipo will cause the cells to become damaged, which in turn can cause ignition of the pack.

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Right, so just making sure I understand this properly (not necessarily for this, just that it's good to get an idea on how to size the fuse for future reference):

- If everything is sized correctly and runs at a lower current than the battery can deliver then there is not too much of an issue with the fuse. Meaning that the fuse doesn't need to be selected for overload on the equipment.
- In the event of a short circuit or motor stall where the current can become considerabley higher than the battery output for long durations then the battery needs to be disconnected quickly to avoid damage etc.
- The fuse needs to be sized pretty much to the maximum output of the battery (in this case 16A output=15A fuse) BUT considering that the fuses do not blow quickly at their rated current it's necessary to de-rate them so they will blow relatively quickly and disconnect the battery ASAP.

Had a look at the data sheet for the fuses and it is relatively clear what you say about automotive fuses:

http://octopart.com/atc-10-cooper-12063#datasheets (Click on link to AT10 data sheet)

Seems that a 10A fuse would take about 1 second to disconnect at about 18A, with a 5A fuse taking 0.1second at 15A.

May start off with a 5A fuse as the drive motors draw nothing and in reality once the motor is up to speed for the spinner then the current draw on that should be minimal. Quite shocking actually as a 15A fuse doesn't seem like it would blow at anything less than 20A and even then it'd take almost ten seconds.

Sounds like a plan.

You should be sizing your pack in order to make sure that your electrical system WON'T overload it, so the only cases where the fuse will become important is if there's a short in which case the fault current will blow it close to instantly.

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Originally Posted by Metal Demons

You should be sizing your pack in order to make sure that your electrical system WON'T overload it, so the only cases where the fuse will become important is if there's a short in which case the fault current will blow it close to instantly.

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Quote:

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Originally Posted by widow_twanky

- If everything is sized correctly and runs at a lower current than the battery can deliver then there is not too much of an issue with the fuse. Meaning that the fuse doesn't need to be selected for overload on the equipment

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Yup, but you also need to consider that the fuse should blow as quickly as possible in the event of a short circuit.

The short circuit current is limited by the ability of the battery to deliver current so if the fuse is too large it either wont blow or will be slow to blow.

Personally I'd rather clear short circuit currents in the shortest possible time (having had a 300mah lipo start swelling on me before and realising that when you say to people 'get out' whilst you deal with it the natural tendancy is for everyone to come into the room and have a look :rofl:). As I recall, tas soon as you remove the current the swelling of the cell stops meaning that if it hasn't exploded by then, it wont. Apart from that short circuit currents aren't good for stuff like speed controllers, receivers and stuff.

If the lipo hasn't exploded by the time it's been un plugged it doesnt nessasarily mean that it's safe. It can sometimes take upto 5 or so minute's for a lipo to catch fire after a short even when disconnected.

The fuse it to reduce the biggest risk of lipo fire's which is shorting them out for prolonged periods.

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Originally Posted by grant_ploughbot

If the lipo hasn't exploded by the time it's been un plugged it doesnt nessasarily mean that it's safe. It can sometimes take upto 5 or so minute's for a lipo to catch fire after a short even when disconnected.

The fuse it to reduce the biggest risk of lipo fire's which is shorting them out for prolonged periods.

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Well that's not good is it, suppose that's the reason for the rule saying you need a bag of salt to cover it in if it gets affected by stuff like that. Makes sense really.

http://www.youtube.com/watch?v=-6VQ6...yer_embedded#!

http://i685.photobucket.com/albums/v...s/9de3f50e.jpg

Any news on when we might have an arena to fight these marvelous beasts?

The arenas Built we just need the polycarb sides