Lipo in heavy

[cliveb]

On the safety issues I think quite a few of us should be taught how to fill gas , charge safely and be as safe as possible.

viewtopic.php?f=104&t=5092

try here :wink:

[kane]

LiPo trials for heavyweights were announced at the AGM this year. Minutes from the AGM are available on the meetings page.

Despite the obvious advances in the technology there remains a very real risk of fire following abuse. However, experience in featherweights has shown that this is highly unlikely. These risks are also easily managed with the use of LiPo bags and chargers with built in balancers.

Whether this scales safely with heavyweights is currently under scrutiny.

[maddox10]

...yes...

If that is your answer to both questions, go to a less unsafe hobby. I can recommend basketweaving.

1) The TV series had a Firepit and Sergeant Bash, Growler had a flame-fart weapon. I believe it was intended to get competitors on fire. Didn't work well.
In 2001 I was using HDPE as armor on Project One. I tested the flame resistance of that rather nice fuel (one of the cleanest solid fuels known to mankind) with a oxy-acy torch. Took ages to get a 12mm plate burning.
Also, short out a good SLA, and the wiring will burn... Burning plastics, Goodygoody.
Short out a bad NiCD with low internal resistance, and you get a cadmium laced smokescreen...

2) Why do event organisers sometimes augment the arena-effects with smoke generators?

[maddox10]

is 2300mah enough? 3 packs of 12v?

For a heavy... Depending on motors, wheelsize and gearratio.

TAN draws about 4.5 Ah from an affordable 36V 9Ah SLA pack during a normal fight. The edge of the capacity of such a set. Bosch 750, big wheels , gearratio 20-1+

Gravity III did about the same, with a Bosch 750, 36V, 20-1 gearratio to 10 kartwheels.

LiPo is a tad more efficient; So a 9S 7000mAh 30C pack sounds perfectly doable for a 2WD machine.

[maddox10]

[quote=terry]http://www.electricwingman.com/power....aspx<br /> On

[widow_twanky]

Is it a problem if a heavyweight robot catches fire in the arena?

Is it a problem if the arena is filled with a cloud of white smoke?

As the smoke from lipo's is toxic the answer is yes to both of these.

The issue here to my mind is that there is a very small risk of this happening BUT if it does then there's no way of stopping a lipo fire until it's burnt itself out. You can put the remaining flames out after its finished but the initial fire will happen once started and each cell will go individually.

Lipo fires are rare and fuses will actually stop the vast majority of those which are thinking about happening. Consequences are quite high. When you do a risk assesment you have to balance the probability and the consequences.

The fire is not sustained by the usual influences such as heat, fuel and oxygen. It is a chemical reaction which once started will not stop until it has finished doing its stuff.

Arenas by their very nature (contained boxes) are not easily ventilated so if it does happen the fumes hang around for a while. As they're full of heavy metals and stuff they're not nice and the 'poisonous' effect is cumulative.

I think the testing will show that lipos can be used safely in a well constructed machine. I also think we need to test some of these to destruction to see how effective safety measures are by introducing heat, piercing some of them, exposure to shock etc etc.

Also we need to get on top of how age and deterioration increases any risks etc. Over time the internal resistance increases which means the heat produced in every fight increases the risk of it happening. That being the case, how do you monitor that?

With stringent rules these could be safe but more research needs to be done but we also need the plan of how to clear them up if they do go.

[maddox10]

As the smoke from lipo's is toxic the answer is yes to both of these.

And is it more toxic than NiCD smoke, or even the smoke from burning insulation?

Lipo fires are rare and fuses will actually stop the vast majority of those which are thinking about happening. Consequences are quite high. When you do a risk assesment you have to balance the probability and the consequences.

I know. A part of my job too.

The fire is not sustained by the usual influences such as heat, fuel and oxygen. It is a chemical reaction which once started will not stop until it has finished doing its stuff.

Not true, any chemical reaction can be stopped.
For Lithium
Remove any oxygen -even in bound form- and the reaction stops.
Remove all heat- and that's difficult, as lithium will reduce CO2 to carbon and oxygen, generating even more heat-

Arenas by their very nature (contained boxes) are not easily ventilated so if it does happen the fumes hang around for a while. As they're full of heavy metals and stuff they're not nice and the 'poisonous' effect is cumulative.

That is why any containment is used for things like painting cars, working with radioactive materials and so on. It's called a ventilation system with filters....

The issue here to my mind is that there is a very small risk of this happening BUT if it does then there's no way of stopping a lipo fire until it's burnt itself out. You can put the remaining flames out after its finished but the initial fire will happen once started and each cell will go individually.
I think the testing will show that lipos can be used safely in a well constructed machine. I also think we need to test some of these to destruction to see how effective safety measures are by introducing heat, piercing some of them, exposure to shock etc etc.

We just need a budget for that.


And I suggest we test a worn out max-power pack (37V 20Ah ) in a thin HDPE foam filled box , lets see how fast that ignites

Also we need to get on top of how age and deterioration increases any risks etc. Over time the internal resistance increases which means the heat produced in every fight increases the risk of it happening. That being the case, how do you monitor that?

Rather simple, good chargers do it on their own.

With stringent rules these could be safe but more research needs to be done but we also need the plan of how to clear them up if they do go.

You can make the rules foolproof, but then mother nature will appoint a better fool.

[widow_twanky]

The smoke from a nicad is probably not worse than that from a lipo but posionous smoke is posounous smoke so not worth debating cos if it kills or seriously injures someone it's has the same relevance. As far as burning insulation is concerned you can get 'low smoke, zero halogen' insulation on cables but it's probably not worth it. The problem i see is in the amount of smoke produced and the speed it is probuced. OK, we're talking worst case scenario here but the toxicity issue is one thing. No-one is going to die from breathing it in (not from poison but you can die from smoke inhalation). Visibility is an issue.

Can debate the scientific theory and the possibility of stopping a lithium fire but the practicalities are very different. On board foam type fire extinguishers are a solution but the weight probably defeats the reason for using them anyway. Easily removable panels to allow you to drop a bucket of sand on it defeat the need to contain the batteries etc.

I agree containment is used for car spraying, toxic installations (part of my job and did a lot of work for Wellcome Foundation in their labs so fully conversant with filters and the like) The problem I see is the practicality of doing this in a mobile arena. Big volume to be ventilated quickly = big fan.

Good chargers will deal with a lot of the issues for lipos but they will not deal with all of them. An increased internal resistance of an undersized battery will generate heat which is the main factor in starting the chemical reaction. In feathers the load is very low (I know about the power drawn for spinners but is this comparable to a stalled mag motor?), there is probably a factor by which the battery should be oversized to provide some headroom for the power discharged when a speed controller throws a wobbly and sticks them in full forward and they virtually stall against the arena wall.

Again, I am sure you will tell me that particular elements of that are wrong but the general point is that a fault in a heavy, particularly if the motors were stalled, would draw significantly more power than in a feather. Over sizing batteries is a way to go but by how much?

This raises the issue of what is the correct fuse size for this? Anyone done some research on the amount of current a particular lipo can take and for what duration?

You can make the rules foolproof, but then mother nature will appoint a better fool. Made me smile that did Absolutely right but that doesn't mean we shouldn't question everything and make it as safe as possible.

Anyways, putting aside all the issues above, if you have a lipo fire and the smoke is contained in the arena and everyone is ok, the time it would take to ventilate the arena would be a commercial issue as it would mean a stoppage of at least an hour (ok a guess but a realistic one) to get back up and ready to go. Is this acceptable even once? Smoke panics people more than fire, it is a much bigger problem in most evacuation situations than flames or heat. It makes people act irrationally and they can injure each other. We talk about containing things in an arena but the smoke will spill out of a net roof and there is probably enough of it to do so from a lipo fire. You cannot guarentee a crowds response, who in the crowd will have a reaction to it etc etc Here's an interesting vid shows people dealing with it quite good to show the amount of smoke produced and time taken to deal with it.

[graeme]

We used one of nippers packs in little flipper at the uk champs pulling 500A and there wasnt a problem with the lipos, also ls4 pulls over 6000w at 37v spinning up fast and either packs could run a heavy so if we werent allowed them in heavys then the feather rules should also be looked at as they have less armour to protect them. Big nipper has 300A fuses on each lipo pack and 200A on the motors so if a motor stalled it would blow, so the 1000A lipos would never be stressed. No problem.

[craig_colliass]

Perhaps the way round this situation would be to have the FRA and EO's to agree on a particular setup for power using LiPo batteries.

So in practice they would say this power battery from this company. Using one of these chargers, batteries must be encased in a fireproof container of these materials of this thickness, when in the robot. People should be able to show this level of competence when using the equipment.

This would show that everyone in the robot sceen has tried to control and minimise risk.