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Thread: MK 24 battery issues

  1. #1
    Senior Member landrover's Avatar
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    MK 24 battery issues

    I received new MK24 batteries in my Permobil F3 about a month or so ago. I was told initially it would take about 15 or so cycles before the batteries reached their peak performance. I was monitoring the performance during that time and was concerned that the battery was draining faster then my previous 34s had. I had a tech from NuMotion come out to check that the batteries were installed correctly and the connections were all intact. He measured the voltage through the controller, also checked the batteries and said they were balanced, and all the connections were good. My concern is that somehow my EZ lock bracket/bolt is causing an issue. The initial tech had difficulty installing the batteries, as she said the EZ lock bolt was installed higher then normal. She had to remove, then reinstall, the EZ bolt to fit the batteries in. The tech that came out the other day mentioned how the batteries sat higher, but did not feel this would impact performance. But getting back to concern about the bolt...it seems days where I lock into my EZ lock in my van, my batteries drain faster. Not sure why/how that would be?

  2. #2
    EZ lock bolt should not have anything to do with the batteries draining faster, unless the bolt is actually causing a battery + post to contact metal on the chair causing a short. Are those chairs able to fit group 24's? I know some chairs with seat elevators can't fit them.

  3. #3
    Senior Member landrover's Avatar
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    Mine doesn’t have a seat elevator. That is my concern, that somehow there is a short. Years ago, my Invacare Arrow was damaged on a flight that bent one of the rear axle assemblies (not sure of the exact term), but every time I’d enter my lockdown at a certain angle, it would cause my chair to shut off.

    On another note...I’m wondering how accurate the controller battery gauge is? My controller gauge dropped one bar today (after minimal use), but when I charged the chair just now, the charger’s green light came on after just 2 hours, which if the battery was weak, would take longer then that to reach full charge.
    Last edited by landrover; 12-22-2018 at 08:22 PM.

  4. #4
    MK batteries are not the quality they use to be. Probably using used lead from china. There warranty is 6 months now not the 1 year like it was. I noticed mine don't last as long either. Lucky I get a year now. Use to get at least 3 years.
    Art

  5. #5
    Quote Originally Posted by landrover View Post
    Mine doesn?t have a seat elevator. That is my concern, that somehow there is a short. Years ago, my Invacare Arrow was damaged on a flight that bent one of the rear axle assemblies (not sure of the exact term), but every time I?d enter my lockdown at a certain angle, it would cause my chair to shut off.
    You can check to see what the "off" current drain on your chair is -- if you have an "ammeter". You can usually borrow one from a local auto-supply store (Pep Boys, O-Reilly, etc.). Or, get one "for free" (with any purchase ) from a Harbor Freight (by waiting for one of their innumerable fliers to come along with the "right" coupon).

    In either case, you would interrupt the battery circuit and install the ammeter in series with the battery pack and the "load" (whatever else happens to be connected to your battery pack -- including a short!). Depending on the chair, this could require temporarily removing one of the connections to one of the batteries for the duration of the test. Or, inserting the meter in place of the (removable/replaceable) fuse that is present to protect the batteries (the ammeter effectively acts as the fuse for the duration).

    You would NOT want to operate the chair with the ammeter in place as you will likely exceed the current carrying capacity of the ammeter (often just 10A). But, then again, you're really interested in the "leakage current" when the chair isn't doing anything! (it won't be 0 because the chair's controller needs to use some power to figure out when you are asking it to "power up"!)

    You can take the reading (hopefully just a handful of MILLI-amps) and extrapolate how much "charge" is being wasted while the chair waits for you to "turn it on". E.g., 10mA for 12hrs is 120mA-Hrs. To put that in perspective, you can look at the output rating of your charger (amps) and guesstimate how long it would take to replenish that lost charge. E.g., a 2A charger would replenish those 120mA-Hrs (0.120AHr) in 0.06 hours (0.120AHr / 2A = 0.06Hr or about 60 minutes/Hr * 0.06 Hr = 3.6 minutes... neglecting losses and inefficiencies)

    Unless you see some outrageous reading, it's probably a safe bet that your batteries are not being unnecessarily depleted. (note that the controller can fail in ways that will also increase the drain on the battery pack!)

    You can also see how much current is actually flowing INTO the battery pack while it is being charged (it may not be what the charger claims to be capable of) using the same technique.

    On another note...I?m wondering how accurate the controller battery gauge is? My controller gauge dropped one bar today (after minimal use), but when I charged the chair just now, the charger?s green light came on after just 2 hours, which if the battery was weak, would take longer then that to reach full charge.
    The battery gauge is a (dirt!) cheap way of indicating "state of charge". It presents an indication of the present voltage seen at the battery pack "scaled up" in such a way as to (hopefully) give you a finer level of detail than the raw voltage display would provide. But, voltage at the battery (and you aren't really seeing it AT the battery when you use the "battery gauge") varies a lot -- based on load, losses in the cable connecting your "gauge" to the battery, temperature, battery age ... AND state of charge!

    By contrast, your cell phone doesn't rely on an examination of the voltage of its internal battery. Instead, it tracks how much you've been using the battery and for how long in order to get a more accurate representation of the "state of charge" -- because phone users are REALLY concerned with how much longer they can continue to use their phone (unfortunately, chair vendors don't seem to think chair users care about this aspect of chair use... D'uh!)

  6. #6
    Senior Member landrover's Avatar
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    I just froze my butt off this morning to test out the battery a bit unscientifically. According to my phone, I went ~ 5 miles on paved uneven surface. I am on my 4th orange bar on the controller gauge. Not sure if that tells anything.

  7. #7
    Quote Originally Posted by landrover View Post
    I just froze my butt off this morning to test out the battery a bit unscientifically. According to my phone, I went ~ 5 miles on paved uneven surface. I am on my 4th orange bar on the controller gauge. Not sure if that tells anything.
    If you were 'froze' please remember our powerchair batteries hate the cold, the colder it is the quicker I've seen range drop off!
    Don't feel bad. I think my batteries are toast, too!
    I rode from bedroom to bathroom and then out to garage, basically across a 3 bedroom house twice and have only the red and 2 orange lights left. I been noticing battery being down to 1 to 3 red at night but think rate of decline has increased.
    Ever notice things come in 3's. Got letter from DriecTV that our equipment is 10 years old and oboslete (SD boxes)that we need to call to update and setup appointment.
    My bedroom TV quit working!
    Now pretty sure batteries are shot!
    MERRY CHRISTMAS!!! And a Happy New Year!
    OH! My van tires are dry rotten, so guess should of said in 3's or since battery problem is a set. meaning 2 then bump bad things come in higher numbers this holiday season! Course could be worst! It can always be worst and has on many occasions.
    So, sincerely ya'll all have a Merry Christmas and a Happy New Year!
    BTW: Ya'll be careful and safe if out and about. Had a couple close calls of people in vehicles not seeing us in powerchairs just this week!
    Last edited by MikeP2013; 12-23-2018 at 01:57 PM. Reason: Add

  8. #8
    Quote Originally Posted by landrover View Post
    I just froze my butt off this morning ...



    ...to test out the battery a bit unscientifically. According to my phone, I went ~ 5 miles on paved uneven surface. I am on my 4th orange bar on the controller gauge. Not sure if that tells anything.
    Unfortunately, no. There's no "standard" by which to calibrate the "fuel gauge" from one chair to another (even of the same make/model). It's like looking at your car's gas gauge and trying to guesstimate how many more miles you've got "in the tank".

    I'm sure we've all had cars that stayed on FULL forever... and then dropped to EMPTY seemingly overnight. As well as cars that slowly progressed to EMPTY and lingered there for 100+ miles.

    The "fuel gauge" in a powerchair is similarly unpredictable. You would have to "keep notes" as to the sort of usage you'd incurred and the resulting fuel gauge displayed -- based on how YOU use YOUR chair.

    You would think that the computer that is inside your chair -- being able to CONTINUOUSLY watch your miles traveled AND the battery voltage AND charging experience -- could "take those notes" and present you with a MEANINGFUL indication of how much "juice" you've got left... based on YOUR specific usage habits! E.g., a rider who is typically driving around hill terrain would expect to have less battery capacity than one who is operating out in the middle of a plain.

    It's time for chair manufacturers to move out of the 1970's mindset and actually put some smarts into their products!

  9. #9
    Senior Member landrover's Avatar
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    Still baffled by battery issues. So as I had mentioned, I felt that I was having issues with my new MK 24s. The longest test I had done was 8 miles, which the battery gauge showed 3 red bars remaining. The DME techs came out on 2 occasions to check the connections and other stuff, all was well. They ended shipping the batteries back to MK to be tested, and all was fine. Meanwhile, the put another brand of 34s in my chair while my batteries were off being tested. Now today I went 8 miles again along the same path as before, and I only dropped briefly by one green bar. So if the typical battery life is ~12-15 miles, there seems to be no way that gauge is accurate (as mentioned in the earlier posts), as you'd expect it to be closer to half full/empty. But then why did the MK24s (which tested fine), drop 6 more bars in the same distance?

  10. #10
    Are the MK's you have GEL or AGM, I was given a set of AGM's a while back and was not pleased with the range at all.

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