MK Gel batteries...

[Burgerman]

Set of newish MK 73Ah gels. On my wrecked old BM1 powerchair. Complete with sticking plaster, hole in gaitor etc. Watch the battery gauge bars DIM every time I accelerate to wheelie. This is with a miserable 80 amp controller, and its been outside for months so water has made it jam on "4" for speed setting...

The 4.5mOhm batteries cannot even cope on the flat on my driveway. The dimming batt gauge is because of severe voltage drop as I load the batteries up. Imagine how bad gels are (or cheap AGMs) on a 120 amp controller! On say a 8.5 mph R-net chair.

You never notice this as a normal user with delays and ramp times set slow like most chairs because its lost in the noise. But here you can both see it and feel it happen clearly. Instead of leaping up/forwards as it does with the Odysseys, the lights just go out...
EG I cannot steer while accelerating...

These MKs came off a TDX SP (I think it was) that didnt go up steep ramps and steer well at the same time. They were new about 3 weeks ago. It does now, it has a set of Odyssey PC1500s instead.

http://www.wheelchairdriver.com/mOhm.wmv Excuse the tatty manky rattly worn out chair! Its unloved!

MKs have good cycle life, and work great in slow delayed, powerchairs with low amp demands. But resistance is too high for anything serious. Even when new/charged.

[Martin O Refurbisher]

That's my experience of MKs too - they plod on

Best,

Martin

[ex-Gooserider]

For whatever it's worth, we just did a road trip to Historic Williamsburg, VA (also visited Jamestown, which was the first permanent English colony in North America... This was a bit of a surprise, we got a call from my sister (who lives in FL) that they had gotten a timeshare, that slept a bunch, and invited us to come down and spend some time with them... It's about half way, so this worked out pretty well, other than that the unit was NOT "accessible" - all the ADA units were booked, so we got a normal unit... Bathrooms had 24" wide doors, so I spent four days w/ no bathroom access - I had to crap in a bucket in our bedroom, and do sponge baths in the kitchen sink...

Because my 1100 had fried a motor, I had to use my backup chair, which is a Pride Jazzy Select 6 that I inherited from my late father... It has a set of used MK's of unknown vintage put in it when I got it, and has mostly just been sitting on the mobility charger for the past year or so...

This is a small wheel chair, that uses a set of U-1 size batteries, and I think a 50A controller. My understanding is that it's mostly a supplemental mobility chair for senior citizens - the kind of thing you get from the Scooter Store scam artists...

Just before we left, I did a rush install of a BM style charging system on it. I was charging at night with the larger mobility charger that I had for my 1100, and during the day by plugging into the van...

Terrain was moderately rough, lots of dirt tracks or gravel trails - they were trying very hard to balance the needs to look "historical" and to accommodate lots of tourists (including HP folks) I did have to worry a lot about battery life, but for the most part I was quite pleasantly surprised by how well the batteries in the chair held up - not fast, but they didn't (quite) die on me, even when I got down to one flashing red light on the meter...

OTOH the meter was pretty useless, not that it's a big surprise... I would have full charge lights showing through probably 80% of the battery life, and then once the first green light went out, I'd go through the rest in pretty short order.

Bottom line - wimpy chair, but even under some pretty hard use, these unknown vintage MK's held up surprisingly well...

As a general note, I'd also give good credit to the staff and management of the Williamsburg areas - there are obvious challenges in trying to make a historic recreation of the late 1500 - 1775 C.E. era accessible, but they did a pretty decent job, lots of buildings had lifts hidden around back or other techniques to at least try... There was also a very detailed list available of every building in the historic area, and exactly what access it had, so you could plan things accordingly... The non-historic restoration stuff, like the museum in Jamestown where they showed the artifacts they had dug up were all 100% accessible, and very nicely done... I wouldn't hesitate to recommend the area to an HP history buff that was interested in the period.

ex-Gooserider

[Burgerman]

That's my experience of MKs too - they plod on

These were only weeks old. But they will/do go on forever. Gradually fading away. But I get exactly the same result or worse from all batteries of the same internal resistance. Its not just MKs. You cant sidestep Ohms and the law... Its everything other than optima/odyssey and presumably the clones that are bad.

After a few months abuse even these better batteries start to do it, and the other cheap AGMs and gels that started off with twice the resistance anyway get even worse.

So for faster 120 amp chairs, heavier people, chairs programmed to "go" then theres simply no alternative but to spend the money on the Odyssey ones. Because controllers and motors are writing cheques the batts cant cash. Remember that that vid was just a wimpy old 80 amp controller! So 160 total. The R-net will try and take 240 amps!