18650a question - advice needed (possibly OT!)

[onebitmissing]

Hi all,

apologies for posting this here but you guys seem to know a *lot* about 18650a cells and I need some advice!!

I'm an above knee amputee and use a wonderful microprocessor controlled knee from Otto Bock called the C Leg (http://www.ottobockknees.com/knee-family/c-leg-microprocessor-prosthetic-knee/). These are however horrifically expensive to buy and get maintained (say $50-60k) or the price of a very nice car....

My "spare" leg appears to have died however I suspect the actual culprit is the battery which I believe is a 18650a though I don't know the exact spec....

I can send the knee to Otto Bock for "service" during which they will replace the battery but this is likely to cost $1-2k (for a battery!).

Having removed the battery the voltage is showing as 0.56..... My plan is to buy a new battery and fit then charge using the standard C leg charger but I am looking for advice on the best battery.

I've uploaded some images of the battery (and leg) here

The only identifying marks on the battery are some text which can be read through the external red cover which say:

OHRM4HE
063419

and also seperately a letter "C"

Any advice/comments appreciated!

onebitmissing

 

[hiuintahs]

Hopefully the on-board charger within the C Leg hasn't gone bad. I'm just wondering since the battery is at 0.56v, if the charger quit working or the battery went bad.

If this is indeed a 18650 lithium ion battery then your best choice would be the Panasonic NCR18650A or NCR18650B. 'A' version being 3100mAhr and the 'B' version being 3400mAhr. (These are a lime-green in color and have black text). And I'd think that you don't need a protected cell type of battery such as would be recommended for flashlights. I think most lithium ion's within electronic equipment manage their own shut down so as to not discharge the battery to a damaging level.

If possible to contact tech support at C-Leg, ask them what type of battery it is.

 

[AnAppleSnail]

The Otto Block C Leg sales sheet Here (PDF, check that this is the right leg) mentions a "Lithium Ion Charger" item. Sales literature says the same, so I believe that you're on the right track.

How technical are you? Can you (Very accurately) measure the dimensions of this cell (It is probably 19mm by 69mm, but check)? If so, you can find physical-fit batteries through the battery nuts here. Next, you'll want to charge the replacement cell in the leg and check its voltage after charge. If it's over 4.20v, or much below that, your charger is bad. If the 'dead cell' voltage is too low (This value depends on some variables, but 3.2v is a good guess), the 'low battery' warning doesn't happen soon enough. Those two things are the fastest way to kill 18650s.

Edit: Now that the manufacturer has posted (?) I see that I misspelled their name. Whoops.

 

[onebitmissing]

The Otto Block C Leg sales sheet Here (PDF, check that this is the right leg) mentions a "Lithium Ion Charger" item. Sales literature says the same, so I believe that you're on the right track.

How technical are you?

Very technical (worked in IT for the last 25 years), still cut code (though it's python/sql these days not C) and am CTO for a tech company and also very mechanical but less electronics...

I have a micrometer and can measure very accurately (without shorting!). The charger is external (I have >1) and works OK with the other knee. There could however be internal circuitry that is dead....

obm

 

[onebitmissing]

If possible to contact tech support at C-Leg, ask them what type of battery it is.

The manufacturer takes a very strong line against anybody touching anything (partially for product liability reasons) and will not help....

 

[Knight_Light]

How much room do you have in the battery compartment? The cell that you took a picture of looks like it might be a Sanyo 2600 mAh unprotected 18650. Some of the larger capacity batteries are larger in physical size as well, especially the Panasonic's.

 

[onebitmissing]

I've just found the model number heat engraved in the red coating - it is a Sanyo UR18650FM so I have ordered identical replacement.

Many thanks for your help!


obm

 

[Knight_Light]

I've just found the model number heat engraved in the red coating - it is a Sanyo UR18650FM so I have ordered identical replacement.

Many thanks for your help!


obm

If there is room in the battery compartment you can go with a bigger battery and get longer run times. It will take longer to charge but you will get a lot more out of it. Although the Sanyo is a quality cell you can get higher capacity.

 

[onebitmissing]

I'd rather keep the identical cell in case it ever goes back to the manufacturer!

Thx

obm

 

[Knight_Light]

I'd rather keep the identical cell in case it ever goes back to the manufacturer!

Thx

obm

Good Point. I did not think of the warranty implications.

 

[Ottobock]

Hi onebitemissing,
Please call us at 800 328 4058 and ask to speak with Tech Support. They will be able to help with your battery questions and find a solution.

Thanks,
Ottobock

 

[garbleduser]

If the charger is the scource of the problem, its probably a blown cap in the charger. If you were to plug it in normaly as if it were charging, and check the voltage across the battery DURRING THE CHARGE and its lower that 4v, replace the cap. Open the charger (if possible) and look at the cap. Is it swollen, bulging, smelling funny, or leaking, just desolder the old one, order another on amazon, and put the new one in!

Hope this gets you back on your feet (sory about the pun),
Adam Nash

 

[stathiskrets]

hi friend.i am an ambutee above knee since 2000.i have a c-leg knee at 2008 but know i have the same problem with you.my c-leg
battery last 3-4 hours only and now it doesn't even charge..have you succesufylly replace the battery on your own?can you tell me how and yhe type of battery you have order...thank you