HK Lipo Bricks - what do I choose and why?

[ElectricGod]

On the subject of replacing bad cells in a LIPO pack. I agree that taking apart an R/C brick possibly means damaging the cells around the failing cell since they are glued or double sided taped together and you have to pull the cells apart somehow.

With practice , care, and a few tricks, cells can be separated cleanly without damage.
A few drops of IP Alcohol and use of a fishing line " cheese cutter". , will be a good start.
Trickiest part is separating the tab connectors (crimped or soldered) and remaking them for the replacement cell.
Again, if you choose the common brick sizes, they are so cheap, it's hardly worth fooling about transplanting cells.

Thanks again to who ever it was that told me about hybrid battery solutions.

..your welcome !
Just goes to prove,...even a god can still learn something on ES. :lol:

Hahahaha...and while I am sarcastic and irreverant, I also know that I am not a "god" of much of anything.

Yeah pulling LIPO packs apart isn't a huge deal if you do it right. That's why I said "possibly could cause damage" . Well sure if you pry them apart with a screw driver...of course you will damage something!!!

 

[Allex]

12AWG gets very hot at 100Amps
[youtube]0DhzWPoSYoQ[/youtube]

 

[ElectricGod]

12AWG gets very hot at 100Amps
[youtube]0DhzWPoSYoQ[/youtube]

LOL! And of course it does...

 

[nutnspecial]

How large of factor is the voltage?

 

[ElectricGod]

Virtually none what so ever. A wire as fine as a hair can carry 1 million volts and never get warm...as long as the current is VERY low. A 12 awg wire can also carry a milion volts and never get warm. However, pass 1 volt at 100 amps and the wire will get hot. Its current flow competing with the resistance of the conductor that generates heat...not voltage. You could take a 20 awg wire and pass 1000 watts though it and never get it warm...as long as that's 1000 watts that is mostly voltage and very little current. Pass 1000 watts down the same wire, but this time its at 100 amps and see how long it takes before the wire is glowing red hot.

This is a useful thing too. Brushless motors have a Kv rating. It is effectively rpms per volt. If you want more RPMs out of your existing motor use more voltage and the motor will spin faster and wont get any hotter...under no load. The down side is you need torque out of the motor or you wont get your EV rolling (load). An increase of torque is effectively an increase in current flow through the motor and now you generate more heat and make the motor warmer. The other big factor is anything moving through the air is a wind dam. At low speeds, you aren't producing much wind resistance. Another way of saying it is you aren't compressing air in front of you and forcing it to flow around you very much. As your speed increases you compress the air in front of you more and force it to have to flow around you more. So to overcome the winds resistance to moving out of your way which increases as you go faster, you have to push harder and that means more torque which means more current which means your motor gets warmer.

Anyway, It's current flow, not voltage that makes the wire get warm.

 

[ElectricGod]

Battery harvesting is going quite well. Most of the cells at least take a charge, but there's some that are weak and have limited capacity. I haven't done any capacity testing yet. That will come after I get through all the cells and have them charged to 100%. Right now I'm just eliminating the dead ones. Since I'll be getting hundreds of laptop batteries over the next months, I wont care about tossing some for being weak. I was surprised that some of the cells were 3000mah cells. Others are who knows what capacity when new. Considering how they are all used, I'm not looking for perfection...just better than 2000mah. They were all 2600mah or better when new so I'm thinking 2000mah is a reasonable "low" or minimum to shoot for.

The battery holders will be here Monday or Tuesday, but the wire and connectors and other bits will get here...if you've ever bought things from China...whenever.

 

[nutnspecial]

Thanks for your answer, I was wondering that when noticing his ps was only 10v.

 

[ElectricGod]

Has anyone found 18650's that have better than 5C discharge? 1 or 2 C looks pretty common. I was looking at the samsung 30Q cells and they are 5C. Most everything I have seen that has 3000mah capacity or more is usually 1 or 2C. Here's a place where LIPO completely eclipses LION. No one thinks much of a LIPO that does 5 or 10C...we all want 20-50C, but in LION (as far as I have seen) 5C is the max.

On a different note...here's what I have harvested from those laptop packs (60-70 cells). Not all are keepers. I'm just starting the capacity testing faze. I've only eliminated the dead ones or cells that won't fully charge so far. I thought of an easy way to test capacity and to eliminate the weak cells. I put them all in battery holders, then go for a ride on just one 20S2P pack until my safety shut-off voltage is reached. I'll unplug that one pack and plug in the next one and do it again until I get through all 7 packs. Then I'll unplug the LION packs and plug in the LIPO's for the rest of the ride. All I will have to do is look for the cells that are run down which will be quick and easy with my cell log. Each pack will have multiple 6S balance connectors on them. Most likely there will be some cells at or very near 3 volts and others still in the 3.5v or higher range. The cells that are at or near 3 volts are the cells that have poor capacity.

The battery holders and wire will arrive today or tomorrow. The balance connectors arrive Thursday. I ordered an 8 position fuse holder so each 20S2P bank can be on it's own fuse. I'll probably go with 10 amp fuses. If I assume 6 amps per bank or 3 amps per cell, then 10 amps will give me a little over head so that I cant pull on the batteries too hard before a fuse pops. If I find 10 amps blows too easily, then I'll go a little higher, but I want to stay within what my 18awg wires can handle easily and the 1-2C discharge of the cells.

 

[liveforphysics]

Test a few LG HG2 we 18650 cells. I got 2.9Ah at 20A constant out of a 3Ah rated cell.

It's around half the internal resistance of most of the 18650s available with over 3Ah.

 

[ElectricGod]

Test a few LG HG2 we 18650 cells. I got 2.9Ah at 20A constant out of a 3Ah rated cell.

It's around half the internal resistance of most of the 18650s available with over 3Ah.

Are those LG's rated at 15C or is that just what you have been able to test them to reliably?

THere's some LG's in that pile, but I don't know what cell specifically.

 

[liveforphysics]

Test a few LG HG2 we 18650 cells. I got 2.9Ah at 20A constant out of a 3Ah rated cell.

It's around half the internal resistance of most of the 18650s available with over 3Ah.

Are those LG's rated at 15C or is that just what you have been able to test them to reliably?

THere's some LG's in that pile, but I don't know what cell specifically.

You asked for something that does better than 5C. They do at least 6.5C, haven't tested beyond, and I don't think they do much beyond.

 

[ElectricGod]

Test a few LG HG2 we 18650 cells. I got 2.9Ah at 20A constant out of a 3Ah rated cell.

It's around half the internal resistance of most of the 18650s available with over 3Ah.

Are those LG's rated at 15C or is that just what you have been able to test them to reliably?

THere's some LG's in that pile, but I don't know what cell specifically.

You asked for something that does better than 5C. They do at least 6.5C, haven't tested beyond, and I don't think they do much beyond.

LOL! I didn't notice my mistake...yeah 15C would be awesome. I'll take 6.5C! That's loads better than most 18650's.

 

[LyonNightroad]

It seems worth pointing out that you can currently pay <$240 a kWhr for Lipo.

http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=66486

 

[ElectricGod]

It seems worth pointing out that you can currently pay <$240 a kWhr for Lipo.

http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=66486

I wonder if they actually have them in stock or if that's a lie. I don't trust HK...bunch of crooks!

The last time I looked at HK batteries, the 6S packs were cheapest when you calculated the price per cell...not so right now.

 

[MrDude_1]

It seems worth pointing out that you can currently pay <$240 a kWhr for Lipo.

http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=66486

I wonder if they actually have them in stock or if that's a lie. I don't trust HK...bunch of crooks!

The last time I looked at HK batteries, the 6S packs were cheapest when you calculated the price per cell...not so right now.

Last time I checked (past few years) the 4s Hardcase truck packs were the cheapest way to go.
The multistar stuff is shaking that up a bit.. depending on if you want more amp hours or more real world current capacity.

 

[Allex]

Some 18650 are 30C but capacity is poor

 

[LyonNightroad]

It seems worth pointing out that you can currently pay <$240 a kWhr for Lipo.

http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=66486

I wonder if they actually have them in stock or if that's a lie. I don't trust HK...bunch of crooks!

The last time I looked at HK batteries, the 6S packs were cheapest when you calculated the price per cell...not so right now.

Because I am deep in the RC Hobby I have ordered over $4,000 dollars worth of stuff from HK. In that time I have gotten 2 defective lipos. This is acceptable to me. The packs I ordered have already shipped. If you pay with paypal there is nothing to fear, they aggressively side with the buyer on almost all issues.

 

[MrDude_1]

It seems worth pointing out that you can currently pay <$240 a kWhr for Lipo.

http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=66486

I wonder if they actually have them in stock or if that's a lie. I don't trust HK...bunch of crooks!

The last time I looked at HK batteries, the 6S packs were cheapest when you calculated the price per cell...not so right now.

Because I am deep in the RC Hobby I have ordered over $4,000 dollars worth of stuff from HK. In that time I have gotten 2 defective lipos. This is acceptable to me. The packs I ordered have already shipped. If you pay with paypal there is nothing to fear, they aggressively side with the buyer on almost all issues.

If you PayPal AND use your credit card... you can hold your credit card over paypals head.

 

[nutnspecial]

+1 Yup^^

I've been wondering about those 4s 2p 16ah 10c multistars - 5x for 20s 16ah.
Are people reliably pulling 70a (4.5C) from them?
My 30c turnigy didn't like 70a on 5.8ah (12 C)

 

[LyonNightroad]

+1 Yup^^

I've been wondering about those 4s 2p 16ah 10c multistars - 5x for 20s 16ah.
Are people reliably pulling 70a (4.5C) from them?
My 30c turnigy didn't like 70a on 5.8ah (12 C)

I am reliably pulling 30amps from a single pack. I do think 70amps is a little sketchy since 30 amps gets a tad bit warm (95F) occasionally.. For this price, why not hook them in 2p for 32ah and a totally realistic 2.2C (This is what I am doing once they arrive).

 

[LyonNightroad]

I don't know if it ever got pointed out but it's pretty unfair to compare the cylindrical volume of top tier loose 18650s to soldered and taped and wrapped Lipos. In practice the 18650s end up behaving more like larger rectangles when assembled, depending on the technique.

 

[ElectricGod]

I don't know if it ever got pointed out but it's pretty unfair to compare the cylindrical volume of top tier loose 18650s to soldered and taped and wrapped Lipos. In practice the 18650s end up behaving more like larger rectangles when assembled, depending on the technique.

Care to explain what you mean?

Lipo's excel in these areas.
Less weight for the same charge capacity than LION...or that used to be the case.
Much higher discharge rates for the capacity of the cell, but that's an over simplification.

LION's excel in these areas.
Higher charge capacity per volume
higher charge cycles regardless of the cell.
Better resilience to abuse, damage and environmental effects.

Typically people use 18650 cells in parallel to get the C rates and capacities found in physically large LIPO bricks. 4 18650's in parallel is the same as a single 10000mah LIPO cell. The multiple cells in parallel also gives better over all discharge rates to the LION pack. Without parallel 18650 cells, you will never get the C rates of better LIPO packs, but then the 18650 is a small cell compared to the large, high discharge LIPO so on a single 18650 vs a single LIPO...keep that in mind. Large LION cells exist with high discharge rates. Keep in mind that a LIPO battery with the same volume as an 18650 would have much less capacity than 2600mah. It would be more like 900 to 1200mah and the C rate would be 2 to 5. LIPOS are great for R/C stuff because they are light weight and have lots of storage capacity. 10,000mah at 30C in a LIPO and the same amount of capacity in 2600mah 18650's you would possibly have about 10-15% more weight and be a much larger battery pack. But that's not all there is to the story. The LION cells will be charging and going strong well after the LIPOs have been thrown out. Also, the 18650 cells are much less prone to damage. On a scale that EV's tend to use the 18650's will also provide more wattage than the same volume of LIPOs. The disadvantage is making a bunch of LIPOs into an EV pack is relatively easy while making an EV pack out of 18650's is harder.

 

[liveforphysics]

It's easily possible for anyone to buy cans that had reliable mfg and QC. I don't even know if hobby cells mfg to EV standards exist.

Hobby pouches get minimum screening and are still largely human hand manufactured. Fully automated 18650 lines are industry standard.

 

[MrDude_1]

It's easily possible for anyone to buy cans that had reliable mfg and QC. I don't even know if hobby cells mfg to EV standards exist.

Hobby pouches get minimum screening and are still largely human hand manufactured. Fully automated 18650 lines are industry standard.

What about the similar pouch cells that Zero uses? are they fully automated?
I always assumed they were... automation makes it cheaper, but if it can be automated, why wouldnt hobby cells be?

 

[liveforphysics]

It's easily possible for anyone to buy cans that had reliable mfg and QC. I don't even know if hobby cells mfg to EV standards exist.

Hobby pouches get minimum screening and are still largely human hand manufactured. Fully automated 18650 lines are industry standard.

What about the similar pouch cells that Zero uses? are they fully automated?
I always assumed they were... automation makes it cheaper, but if it can be automated, why wouldnt hobby cells be?

Yes, fully automated and extensive post mfg QC like virtually all EV cells. Many hobby grade pouches get a voltage check after formation, and little QC beyond this.