Wheel Chair Batteries

Dabbler

Wondering if anyone has experience and/or recommendations for care of electric wheel chair batteries.

I know its not exactly a "solar" question, but its about battery care which is related.

A friend of mine is a c7 neck break partial quadriplegic and is dependent on an electric wheel chair, and thus the batteries.

I think the batteries are sealed lead acid or AGM. She was given advice that the batteries had a "memory effect"' like a NiCd and so should drive them to the bottom before recharging. I think this advice is incorrect. I have encouraged her to top them off every night. Thoughts/advice?

Also, the charger is a wheelchair specific device. It seems to support bulk and float charging. Do these batteries need to be equalized once in a while?

niel

Re: Wheel Chair Batteries

it is really hard to advise let alone comment on this because we aren't sure what type of battery she really has as they could be agm, gel, nicd, nimh, etc. nicd batteries are the ones people complain about for memory. as to eq charging them, don't bother. if you wish, you could rearrange the batteries and that could even things out too without excessive charging that eq brings even on batteries that normally don't get eq charges as some nicd and nimh batteries end batteries stress somewhat.
ps sorry to hear of her disability.

System2

Re: Wheel Chair Batteries

Seriously Dabbler, more information is needed before proper advice can be given. I'm sure there is advice to be given, which could have a great impact on the lives of those batteries, but we have to first know what we're dealing with.
Perhaps the provider of the wheelchair can supply the battery type etc, or is there a name and number on the batteries?
Proper maintenance is a serious concern.
Regards
Wayne

Dabbler

Re: Wheel Chair Batteries

Thanks, you're both right. More detail needed. I know better, sorry for the brain fart!

The chair is an Invacare Ranger X, and uses these batteries:

http://www.apexbattery.com/invacare-action-ranger-x--ranger-ii-wheelchair-battery-wheelchair-batteries-invacare-wheelchair-batt.html

That says the batteries are valve regulated sealed lead acid gel chemistry, 60 amp hour X 2 batteries. Isn't it true that they should be kept topped off, and not run to the ground before charging?

Also, a second set of batteries (but older) exhibits significantly less battery capacity. I have sometimes "revived" normal lead acid batteries with an eq or two I but I don't know if you do that to SLA gels.

Thanks for any recommendations you may have.

System2

Re: Wheel Chair Batteries

Dabbler wrote: »

That says the batteries are valve regulated sealed lead acid gel chemistry, 60 amp hour X 2 batteries. Isn't it true that they should be kept topped off, and not run to the ground before charging?

You are so right!!!! To run these batteries flat is nothing short of murdering them. They should never (if possible) be discharged below 50% and preferably not more than 20%, leaving 80% still in the batteries. They should also be recharged after every days use.
`Lead-Acid batteries do NOT have a memory, and the rumor that they should be fully discharged to avoid this "memory" is totally false and will lead to early battery failure.`

You will find EXCELLENT information here:

http://www.solar-electric.com/deep_cycle_batteries/deep_cycle_battery_faq.htm#Cycles%20vs%20Life

Also:

http://www.trojanbattery.com/BatteryMaintenance/Discharging.aspx

Hopefully the batteries haven`t already been damaged too badly.
Cheers and all the best.
Wayne

BB.

Re: Wheel Chair Batteries

Basically, the NiCAD "memory effect" was a very specialized issue dealing with satilites which went through hundreds of charging/discharging cycles that were exactly the same (same amount of current draw, exactly the same sun/dark cycle time)... This caused the place where the discharge "event surface" to stop at exactly the same place in the cell each time. And this causes the NiCAD structure to form larger than normal crystals right at that interface. The large crystals (as I understand) probably have less surface area than the numerous small crystals that form when charged and discharged through the various crystal "boundaries"--which caused voltage depression because these large crystal areas could not support the expected discharge current when the cycle went "deeper than normal".

Just as everyone is running around and saying that the memory effect is a myth, here I am, saying that it is true. OK, so, why is this? First of all, the term memory effect is quite unscientific. People tend to attribute any failure of a NiCd to memory.
Let us define memory as the phenomenon where the discharge voltage for a given load is lower than it should be. This can give the appearance of a lowered capacity, while in reality, it is more accurate to term it voltage depression.
Memory is also hard to reproduce, which makes it hard to study. Originally, memory effect was seen in spacecraft batteries subjected to a repeated discharge/charge cycle that was a fixed percentage of total capacity (due to the earth's shadow). After many cycles, when called upon to provide the full capacity, the battery failed to do so. Since we aren't in space, the above is not really relevant...
Let us look at various causes of "memory" or voltage depression.
Memory can be attributed to changes in the negative or cadmium plate. Recall that charging involves converting

Cd(0H) to Cd metal.
2
Ordinarily, and under moderate charging currents, the cadmium that is deposited is microcrystalline (i.e. very small crystals). Now, metallurgical thermodynamics states that grain boundaries (boundaries between the crystals) are high energy regions, and given time, the tendency of metals is for the grains to coalesce and form larger crystals. This is bad for the battery since it makes the cadmium harder to dissolve during high current discharge, and leads to high internal resistance and voltage depression. The trick to avoiding memory is avoiding forming large crystal cadmium. Very slow charging is bad, as slow growth aids large crystal growth (recall growing rock candy). High temperatures are bad, since the nucleation and growth of crystals is exponentially driven by temperature. The problem is that given time, one will get growth of cadmium crystals, and thus, one needs to reform the material. Partial cycling of the cells means that the material deep with the plate never gets reformed. This leads to a growth of the crystals. By a proper execution of a discharge/charge cycle, one destroys the large crystal cadmium and replace it with a microcrystalline form best for discharge.
This does NOT mean that one needs to cycle one's battery each time it is used. This does more harm than good, and unless it is done on a per cell basis, one risks reversing the cells and that really kills them. Perhaps once in a while, use the pack until it is 90% discharged, or to a cell voltage of 1.0V under light load. Here, about 95% of the cells capacity is used, and for all intensive purposes, is discharged. At this point, recharge it properly, and that's it.
The more common "memory effect" isn't memory at all, but voltage depression caused by overcharging. Positive plate electrochemistry is very complicated, but overcharging changes the crystal structure of the nickelic hydroxide from beta-Nickelic Hydroxide to gamma-Nickelic hydroxide. The electrochemical potential of the gamma form is about 40 to 50 mV less than the beta form. This results in a lower discharge voltage. In a six cell (7.2v) pack, this means a loss of 300 mV. Trick? Don't overcharge. Leaving cells on a trickle charger encourages formation of gamma nickelic hydroxide. Expect the cells to discharge at a lower voltage.

NiCADs and NiMH do take deep cycling very well... But any battery chemistry can be destroyed when either Over Charged (causes overheating and possible venting of water/electrolyte) or deep discharging where a series string of unmatched cell capacities actually "reverse charge" one or more cells (reverse cell polarity). VLA/Sealed/AGM/NiCAD/NiMH all can be damaged this way.

Lead Acid batteries further don't like being stored at less than 75% of capacity for more than a day--the Sulfates (normal discharge chemistry) harden and will not return when the battery is recharged. Most Lead Acid batteries cycle life will dramatically fall if cycled below 50%--and especially if not immediately recharged.

Some AGM batteries (all?), because of their construction, are not supposed to experience sulfate hardening and can be cycled to 20% state of charge.

VLA and other sealed batteries are very sensitive to over charging (vent electrolyte when overheated/charged). Gell Cells are not very rugged batteries at all and should be avoided--if possible.

Most batteries are OK when stored at 100% state of charge--and many can be trickle charged with a low current / lower than charging voltage (see battery manuals).

Other batteries, such as Lithium Ion, don't like being stored at 100% charge as they will have a short lifetime.

Here is another Battery FAQ with descriptions of various battery chemistries and how best to store them.

By the way, I have figured out a neat way to "trickle charge" batteries in storage using their own cheap wall wart chargers that come with various rechargeable appliances (or used to trickle charge car/tractor batteries when in storage)... This chargers almost always will overcharge the batteries (and cause damage) if left plugged in for more than 1/2 a day--let alone leaving them plugged in 24x7 for 9 months--then you need the tool/light because your power went out in the storm... What I have done is to put a regular lamp timer set for 1 hour per day (or whatever you have measured/estimated is the correct cycle time) to power the wall wart... Reduces the average charge current to 1/24th of the wall wart capability, which keeps the battery charged--but not overcharged/overheated.

-Bill

icarus

Re: Wheel Chair Batteries

Bill,

Once again you impress me with the depth of your knowledge and your research!

So,, all these years I have been putting the dying drill battery in the drill with a rubber band on the trigger has really been killing them rather than prolonging their life? Huh! I guess I will have to change decades of practice.

I noticed on my latest NiCd battery drill, the manual call for NEVER completely discharging of the battery. Now it makes some sense. I'll try it for a while to see if I get better battery life.

Next question (off topic of course!) is should I keep my NiMh computer battery plugged in and fully charge all the time, or should I leave it unplugged until I have dropped the soc a bit?

Icarus

PS I know that the NiMh batteries in the Prius are never "fully" charged, and they are never allowed to discharge more than ~50%

BB.

Re: Wheel Chair Batteries

Icarus,

From my 2 cents... The earlier link:

NiMH (Nickel Metal Hydride) Battery Storage
Duracell NiMH Battery Storage

Ni-MH batteries can give years of safe and reliable service if they are used in accordance with recommended procedures and are not abused. Batteries should be kept clean and dry both during use and storage. They can be stored for many months in a charged or discharged state without any detrimental effects as long as they are not exposed to extreme temperatures for any long period of time. After periods during which the battery has not been used, the battery should be charged before being placed in service. Extended overcharging or overheating of the battery should always be avoided.

Varta NiMH: Battery storage in any state of charge is possible. Storage temperatures between -20 and +35 are recommended, relative humidity approximately 50%. In case of long term storage cells must be recharged once a year.


Sanyo NiMH: Under the recommended storage conditions (-20 C to +35 C) the Twicel can be stored indefinitely in either a charged or uncharged state. Recovery may take several cycles. If a battery is stored for a prolonged time connected to a load, electrolyte fluid will leak, the battery will begin to deteriorate, and capacity will be impaired after storage. During long time storage battery deactivation may tend to occur, and for this reason charging may stop early during recharging after storage. This problem can be solved by charging and discharging the battery several times.
Sanyo NiMh Battery Storage: Generally speaking, a loss of voltage and capacity of batteries due to self-discharge during storage is unavoidable. The factors inducing this self-discharge of Nickel-Metal Hydride batteries is listed below:

1. The inside of the cell is a hydrogen atmosphere at low pressure, which gradually reduces the active materials at the positive electrode, resulting in a drop of cell capacity. Accompanied by this, the negative electrode which is thermodynamically unstable in its charged state gradually gives off hydrogen gas, thus reducing cell capacity.
2. The active materials at the positive electrode in its charged state self-decompose, causing the cell capacity to decrease.
3. Impurities within the cell, especially nitric ions, are reduced at the negative electrode and diffuse to the positive electrode where they are oxidized. This results in a lowered cell capacity.

The factors (2) and (3) also apply to Nickel-Cadmium Batteries. As discussed above, the self-discharge of Nickel-Metal-Hydride Batteries during battery storage causes a loss in stored energy. However, once recharged, this lost portion of the capacity will be almost completely restored. The self-discharge characteristics of Nickel Metal Hydride batteries is affected by storage temperature. . . If the battery is stored at high temperatures, the self-discharge will be accelerated. Also, the longer the storage period, the more the cell capacity decreases. As mentioned above, since the capacity of Nickel Metal Hydride batteries lost by self-discharge can be restored by recharging, there are virtually no noticeable adverse effects of battery storage. However, prolonged storage at high temperatures may deteriorate or deform the gasket or the separator, and should be avoided. Either fully charged or discharged, Nickel Metal Hydride ( NiMH ) batteries may be stored indefinitely. . . In either cased (charged or discharged) the capacity is recovered within two or three charge / discharge cycles.

Panasonic NiMH Battery Storage

Because long term storage can accelerate battery self-discharge, and lead to the deactivation of reactants, locations where the temperature ranges between +10°C and +30°C are suitable for long term storage.

When charging for the first time after long term storage, the deactivation of reactants may lead to increased battery voltage, and decreased battery capacity. Restore such batteries to orginal performance by repeating several cycles of charging and discharging.

When storing batteries for more than one year, charge at least once a year to prevent leakage and deterioration of performance due to self-discharging.

So... If the tool/appliance has a small drain, disconnect the batteries for long term storage. If the battery device has no leakage current--leave pack in.

Don't keep on charger. Only recharge before use, or, if needed to be kept charged for an emergency--use my trick of a lamp timer set to turn "on" only and hour or so per day--will keep battery pack charged without (to much) chance of overcharging.

If you need NiMH batteries that should retain their charge between use (for months or longer), take a look at the AA and AAA Sanyo Eneloop batteries (and other "hybrid" / "pre-charged" NiMH batteries). They are supposed to keep 85% of their charge after one year of storage.

-Bill

icarus

Re: Wheel Chair Batteries

Bill,

Once again for the helpful information.

What is not addressed there is; should a NiMh lap top be plugged in while 24/7 and while in use if you can, or are you better letting it draw down a while and then charge it? I surmise the latter.

Icarus

System2

Re: Wheel Chair Batteries

Awesome info Bill!
Thanks a lot. Really appreciate it.
Wayne

BB.

Re: Wheel Chair Batteries

I leave my laptop, with battery, plugged in 24/7... It only charges for a few minutes randomly (usually only if I have unplugged it to move to another room and/or ran on battery for a bit rather than moving the cord).

My laptop should run more than 2 hours on a charge--but now it seems to die in 45 minutes or so... But it is probably 6+ years old and the battery is also my UPS--so I take it as price of having a 100% UPS'ed computer as corrupted data/disk is probably worse than buying a battery every 5 years (and in reality--probably a new laptop every 5-8 years).

I don't think that a UPS battery (probably gel cell) will last more than a year or so in one of the $100 UPS's (probably going unplug my desktop UPS--battery will only last a minute or so--and seems to burn more power than I would want while the computer is turned off 95% of the time).

-Bill

crewzer

Re: Wheel Chair Batteries

Ref: http://www.apexbattery.com/invacare-action-ranger-x--ranger-ii-wheelchair-battery-wheelchair-batteries-invacare-wheelchair-batt.html

Link to battery manufacturer's "maintenance instructions": http://www.universalpowergroup.com/Downloads/safety.pdf

Link to useful technical guide for VRLA (AGM and gel) batteries: http://www.mkbattery.com/images/VRLA_TechManual.pdf

HTH,
Jim / crewzer

Dabbler

Re: Wheel Chair Batteries

Thanks to all of you for the great info, comments and suggetsions!!!!