External 36V Li-ion batterypack Hilti TE 6A

[kmjelle]

I use a Hilti hammer drill for technical climbing purposes, and want to make an external battery pack to keep on my harness or in my backpack, to save weight when working above my head. Capacity should be around 3Ah, 36V. Any suggestions as to which cells I should go for, Li-ion or Li-polymer?

Just measured the currentdraw on my 12V Metabo to around 10A, when it was working moderately hard. It has a Ni-Cd battery. Are such high currents a problem for Li-ions? It usually lasts for bursts of 15-20sec.

I have made Li-ion packs for led lights, so I am familiar with soldering and the use of PCBs.

 

[Anders]

Hello kmjelle.
Welcome to CPF.

The best cell for you is probably A123 (28650) cells.
70A continuous discharge ...

Hard to find, members on rcgroups usually buy DeWalt 36V packs on Ebay.
More than 100$ now.....
http://www.rcgroups.com/forums/showthread.php?t=822895&highlight=A123+DeWalt



Anders

 

[kmjelle]

I see. So 10 series connected 3,7V, 2,6Ah 18650 Li-ion is not an option?

 

[Handlobraesing]

I see. So 10 series connected 3,7V, 2,6Ah 18650 Li-ion is not an option?

Don't play with lithium ion cells like ordinary batteries. You need the means to make sure each cell stays above minimum voltage and comes up precisely to 4.15v to 4.20v during charge, never exceeding 4.2v, if you do, the stressed cell might rupture or catch fire.

 

[Mark620]

Just measured the currentdraw on my 12V Metabo to around 10A, when it was working moderately hard. It has a Ni-Cd battery. Are such high currents a problem for Li-ions? It usually lasts for bursts of 15-20sec.

YES it is a problem.


The amperage draw rate on the Hilti is too high for a single set of batteries.
You would have to use parallel sets of batteries to achieve safe discharge rates..
You do not want these batteries exploding/catching fire in your pack/on your back while bolt climbing.

See this thread: http://www.candlepowerforums.com/vb/showthread.php?t=117117

NSS 55638

 

[kmjelle]

Are you saying that 10S2P of 18650s could do the trick?

Where can I buy Molicells? They seem to be hard to find.

Could http://www.dealextreme.com/details.dx/sku.5035 be an option, even though they are probably not 5Ah.

 

[Anders]

Hello kmjelle.

You can't use normal Li-Ion cells for this like those in your link.

When you charge them you must balance each cell to avoid venting.

This thread is very informative.


Anders

 

[LuxLuthor]

Are you saying that 10S2P of 18650s could do the trick?

Where can I buy Molicells? They seem to be hard to find.

Could http://www.dealextreme.com/details.dx/sku.5035 be an option, even though they are probably not 5Ah.

Check the listings in this thread.

 

[kmjelle]

Which of these two cells would be the cell of choice for my application: http://www.hobbycity.com/hobbycity/store/uh_listCategoriesAndProducts.asp?catname=LiFePo4&idCategory=218&ParentCat=85 Is the cheaper one suited for the job?

 

[SilverFox]

Hello Kmjelle,

Welcome to CPF.

The A123 cells have proven themselves and are a known item. The RC people are using and abusing them daily, and they are finding that they perform very well and are very difficult to damage.

Yuntong batteries are basically unknown. Their battery philosophy is different from any other battery manufacturer. They are the only manufacturer that recommends charging NiMh and NiCd cells at 0.33C, not higher. They give a fast charging option, for most of their product line, of a 0.33C charge rate for a time limit. If you completely discharge every time, this works, but it does not work in a partial discharged situation.

Everyone else recommends using charge termination controls and to charge in the range of 0.5 - 1.0C.

This may simply be an oversight, but without actual test results, you need to begin to form an opinion based on something.

If you have time, pick up some of the Yuntong cells and send them to me for testing. I will return them afterward. Then we will have an idea of how well they would work. If you don't have time, spend the extra money on the A123 cells.

Tom