Splitting power out

[Coolspeedbot]

oh I see, now it makes sense the fuse acts as a fail safe in a way.

part of my confusion and the reason why I asked about the rules relating to them was that Jamie's example of a circuit was the first I had seen that uses a fuse.

and yeah fair point Gareth the FRA rules are there for a reason but my dyslexia often makes me miss stuff, I also find it easier to understand stuff through the wording of other robot builders.

[Coolspeedbot]

seeing as we're talking about electronics, could someone explain what makes a charger, a balanced charger for lipo batteries?

is it as simple as, one that has the same charging port as the lipos?

I was thinking of using one these:

http://www.hobbyking.co.uk/hobbyking...Lipo_Pack.html

I only asked as I can't seem to find anything thats clear on balance chargers in the forums.

[Garfie489]

A balance charger will have a port for the white block you see with (in this case) 5 wires coming out of it. Generally any charger described as being for lipos should have a port for that somewhere (though may require an adaptor).

Btw only reason im abit hands off with regards to safety in text is because you need to understand it rather than be told. If i know you or was there in person itd be a different matter, however as an extreme example if i told you how to fire a gun but forgot to tell you not to aim it at people then thats kinda on me for not giving a full instruction.

[daveimi]

Fuses

A fuse just melts when the running gear of the robot pull too much current for whatever reason. Lipo batteries and speed controllers have a knack of catching fire quick when they get past the rated amps. So, if you stick a fuse in rated at the max amps everything should be running at, it will pop before

a/ the robot catches fire and burns everyone alive

and

b/ ruins all your expensive robot clobber.

You will notice a lot of robots using the fuse AS the removable link. This is because fuses need a circuit connection and to be easily removable from a fuse holder for changing, thus making them by proxy the ideal removable link.

Lipo Chargers

Lipo batteries use a chemical compound that can only produce 3.7 (ish) Volts. To make a 12V battery or whatever, you need multiple sacks in your battery full of the compound. They then get wired together to produce voltages in multiples of 3.7V. A 2S batterry is a "two-sack" in Dave speak, so means 2 x 3.7V = erm...7.4V. When discharging, the sacks will give off energy altogether, but to be charged each sack needs to balanced. This is where you have a Lipo Charger with a power plug and a balance plug. The balance plug is an extra connection from the charger to each individual "sack" in the battery so that they all charge evenly in the same rate. Otherwise, they get hot, blow up, and again, burn everyone alive.

For any more Dave explanations, just ask

[Eventorizon]

Sorry to correctly you David but some of that is wrong -

Each Cell of a LiPo (not Sack), has a nominal voltage of 3.7V (This is the voltage that anything plugged into the LiPo will see when its under load). When fully charged a LiPo has a voltage of ~4.2V per Cell. You never really want a cells voltage to drop under that 3.7V nominal, but its not the end of the world if it does go to say 3.5V or even 3.4V, anything lower and you can start to cause damage. Some ESC's have built in cut offs that you can adjust to your liking, the default is usually 3.2V per cell.

LiPo's must be balanced when you have more than 1 Cell wired together, in series or parallel (Which in the case of fighting robots is 99% of the time unless you are talking about Antweights). Cells at different voltages have different internal resistances and are also trying to move electrons at different speeds, which will cause damage, produce heat, and potentially cause fires.

The balancing process is done automatically by a Balancing Charger, such as the Turnigy Accucel 6. It charges the LiPo but measure all the cell voltages at the same time and can charge/discharge 1 cell individually if it falls behind/goes over the others.

You need not worry if you measure a Pack and find that the highest cell might be 4.21V when charged and the lowest 4.18V. 0.03V won't cause an issue. But I would be concerned if it was more like 4.2V and 4.0V.

[joey_picus]

I've used 2 cell lipos without a balancing charger (but with a lipo-specific non-balance charger, I'm not plugging it into the wall or using a funnel to feed electrons in) for years and years in antweights and never had any issues with them, but the advice holds for anything where batteries cost more than £5 to replace.

I can reccommend the Accucell-6, the manual is a little impenetrable (such is China) but it does a very good job very nicely for me. And it's black and yellow, what more could one want?

[Coolspeedbot]

ohhhhhh I see.

[daveimi]

Of course lipo's have sacks in, they make them from the same hessian santa uses for his sacks haha

[Coolspeedbot]

Found these handy videos on the wiring of a combat robot, including a video on making a removable link.

https://www.youtube.com/watch?v=8kxCR5i9f7c

https://www.youtube.com/watch?v=IktcgbzK2Ow

https://www.youtube.com/watch?v=bVjqrTv1KRI

https://www.youtube.com/watch?v=vLIN9FpaE9M

[Coolspeedbot]

just to get a general idea, when you guys are attending events that run over multiple days, do you guys put your lipos into 'storage' charge after each day? or do you leave some, fully charged, over night?

and besides lipo sacks, do you guys used anything else to store your lipos when they're not in use? because I'm thinking of getting a box to put them in.

in my case I was thinking of storage charge all my spare batteries, and leave one fully charge over night for use in the first fight the following morning (If my bot hasn't been trashed or knocked out).

[RogueTwoRobots]

Storage charge is only required when you're not going to be using them for a long time, a number of weeks for example. At an event this isn't necessary, so just charge them all up the night before, ready for the next day. They need to be in the lipo sack when charging but if leaving them overnight once they're charged, it's fine to store them somewhere such as a box, so long as they're safe. Many choose to leave them in the lipo sacks as a precautionary measure though.

[Coolspeedbot]

Oh ok, now I just need to worry about some 2mm metal sheets to surround the battery when it's in the bot, then my research and planning phase will be (sort of) finished and I can start the build phase.

[typhoon_driver]

If you want a ready made box that will happily store them, look at buying an old ammo storage box like one of these

http://www.ebay.co.uk/itm/Army-Ammo-...UAAOSw4HVWEWTY

Plenty more sources available on ebay and they are perfect for keeping them contained should the worst happen.

[Coolspeedbot]

If you want a ready made box that will happily store them, look at buying an old ammo storage box like one of these

http://www.ebay.co.uk/itm/Army-Ammo-...UAAOSw4HVWEWTY

Plenty more sources available on ebay and they are perfect for keeping them contained should the worst happen.

oh that's good, thanks Gary

[Coolspeedbot]

Just going back to the discussion on fuses, I found fuses for this battery:
http://www.hobbyking.co.uk/hobbyking...Lipo_Pack.html

But I was thinking of using this LiPo instead:
http://www.hobbyking.co.uk/hobbyking...Lipo_Pack.html

but doing the maths for the rated amp of the battery and its burst discharge, but the only fuses I can find are 100amps and 150amps, seeing as the rules say the fuse has to be rated under the max burst discharge will the 100amp fuse handle the 5cell Lipo?