Lipo for Dummies part II

[bigisland]

Ok so I know what KFF are and now I'm movin on to the real deal!
Wondering about a few things on these battery set ups, see drawings for questions.
How much do you need to be concerned with sparking when unplugging your pack from the main harness ( wiil it just damage your connector, whats the best way to deal with this?

Thanks

 

[dogman dan]

Both diagrams look good to me. Questions about guage of wire and connectors depends on the amps you will be drawing.

I tend to use 12 guage wire, and 45 amp anderson contacts and housings for my wiring harnesses. Adequate for my controllers, the biggest of which is a 40 amp lyens 12 fet. 12 guage instead of 10 because it crimps and stuffs into 45 amp andersons easier than 10 guage.

If I was to do it all again now though, I'd be looking a bit more at using the bullets for more of the wiring, and fatter wire, on the bike with the big controller.

The spark is not a big deal till you get into 72v, 100v etc. Andersons do have one nice feature, they handle the spark well. They char on the tip, but then slide in and make contact on a clean spot.

 

[Drunkskunk]

SParks are caused by the sudden rush of power to charge the capacitors in the controler. Some tollerate this better than others. at 36 volts, ignore it. at 72 volts, It might cause the caps to blow out eventualy, maybe. It happens. The more imediate problem is the slow eroding of your connector. each spark is burning a pit in your contact, and will eventualy ruin the connector.

The solution is called a precharg resistor. basicly its a resistor that allows the capacitors to charge up slower, say, a half a second, then lets you have full power. Plenty of ways to make this work. the simplist is to have 2 positive conectors to the battery. the first has a 100 ohm 1/4 wat resistor inline. the second is your regular connector. plug the resistor's line in first, then the regular line.

Or you could use an inline On/off switch on the main power wire, with a 100 ohm resistor shorting out the 2 poles of the switch. when "off" the power goes through the resistor. So you plug in the battery with the switch "off" then turn it on. No spark, no power surge. You just have to remember that power is always "on" with that switch, just not full power.

 

[Spacey]

Just built two of these:

3 packs of 5.8Ah 8 Cell Turnigy Lipo so in total that's 1.15KW of battery power at 66v, it looks bad as I have not put the foam protection over it yet. Soldering 8Awg to 10Awg was a pain in the arse.... had to buy a 120 watt equiv Butane soldering iron.

 

[neptronix]

Sorry for the OT, but sweet akai..

 

[bigisland]

Or you could use an inline On/off switch on the main power wire, with a 100 ohm1/4 wat resistor shorting out the 2 poles of the switch. when "off" the power goes through the resistor. So you plug in the battery with the switch "off" then turn it on. No spark, no power surge. You just have to remember that power is always "on" with that switch, just not full power

That seems simple enough, so on sizing the resistor is 100 ohm1/4 watt good for 48 or 72 V ?

And what type of switch do you need any thing special?

 

[julesa]

Or you could use an inline On/off switch on the main power wire, with a 100 ohm1/4 wat resistor shorting out the 2 poles of the switch. when "off" the power goes through the resistor. So you plug in the battery with the switch "off" then turn it on. No spark, no power surge. You just have to remember that power is always "on" with that switch, just not full power

That seems simple enough, so on sizing the resistor is 100 ohm1/4 watt good for 48 or 72 V ?

Don't bother with the resistor or the switch at 48V.

And what type of switch do you need any thing special?

One where you won't accidentally leave the switch "off" and then try the throttle. If something tries to draw power while your modified switch is "off," it could get toasty very fast. A 100 ohm resistor will be briefly absorbing 50 watts with 72V across it. If you choose to go 72V I'd be inclined to use a 470 ohm resistor (might take something like 2.5 seconds to charge the caps, instead of half a second) and probably bigger than 1/4 watt, though that's not critical for just charging controller caps. The worst case with a 470 ohm resistor at 72V would be 11 watts.

The switch will need to be rated for the amount of current you're going to put through it. Voltage rating won't matter as much, since the resistor should already have the voltage equalized before the switch is turned on.

 

[snellemin]

12 awg is more than enough for most setups. How many really pull 40A continuous? I was fine with Dean connectors. I just updated my wiring harness and went with 5mm bullet connectors and precharge resistor setup. I'm running 20S1P lipo and use two 1W 100 Omhs resistors in parallel. The resistor part uses 3.5mm bullets. I hook up my negative first, than the precharge cable and then the main positive wire. Zero sparks.

 

[Spacey]

Sorry for the OT, but sweet akai..

I love the old S950 12 bit samplers, loads of character for drum loops.

 

[bigisland]

Snellemin , thanks for those pics, what brand bags are those are they from a bicycle company or are you just adapting them , are you just putting your lipos in there with out any impact protection?

 

[snellemin]

Snellemin , thanks for those pics, what brand bags are those are they from a bicycle company or are you just adapting them , are you just putting your lipos in there with out any impact protection?

I'm using Acepow 4s hardcase lipo's. I had some high speed crashes in my 1/8 scale RC and the lipos survived them all. So no other protection is being used.

The bags I got from Ebay and they are $5.50 shipped.
http://cgi.ebay.com/New-BLUE-Bike-B...ultDomain_0&hash=item3cb547c59b#ht_796wt_1150

 

[bigisland]

Thanks for that link Snellimin, how much lipo will fit in each bag , looks like you all so have some in the mesh on the top of the bag? is the quality of the bags decent?

 

[snellemin]

Each side bag holds a 4s hardcase and the middle mesh cellphone holder holds a 2s hardcase lipo. Quality is decent and can't complain really.

 

[bigisland]

I forgot to ask about the balaninc wires can some one confirm that I got this right, Thanks!


If you have lipos permanatly paralled their balancing leads are also permantly paralled?

If you series these sets the paralled balancing leads do not get connected in any way?

And lets say you have a 12s charger and you are charging a battery pack made of two sets of paralled 6s lipos, that are series connected, so you have a 12s 2p pack.

you would then plug the + and - comming from the overall pack in to the charger. And then would you plug the two 6s balancing plugs into the charger? or will the charger have a 12 s conector ?

 

[julesa]

If you have lipos permanatly paralled their balancing leads are also permantly paralled?

Yes

If you series these sets the paralled balancing leads do not get connected in any way?

Certainly not from one parallel sub-pack to another parallel sub-pack wired in series with each other. Snap-flash-melty-fire-badness.

I'd be surprised if you'll get a good answer your other questions without a better picture of what you have in mind. Like for example, what charger you're talking about. I'm still new to Lipo, but I know enough about batteries and electricity to be confident I'm not going to make any mistakes wiring things up. Be confident that you know what you're doing before you start. People who know exactly what they're doing still get KFF sometimes. The results of a short circuit are more impressive when the internal resistance of the power source is very very low.

Not sure whose KFF this is, likely someone here though.

 

[bigisland]

I'd be surprised if you'll get a good answer your other questions without a better picture of what you have in mind. Like for example, what charger you're talking about.

Well the two drawings I posted in the beginning pretty much shows the basic parallel/series and series/parallel, but I left off the balancing wire part. I am going with the Hyperion charger.

Keeping the polarity correct in the battery harness design is really pretty simple stuff, looks like most people make connection mistakes when the break down and reconnect their packs because their connectors aren't polarized.