Help Needed with Mobility Scooter Batteries

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ghostcat
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Help Needed with Mobility Scooter Batteries

Postby ghostcat » Wed Jan 16, 2013 2:14 pm

I hope you don't mind me posting here. I have a problem with the batteries on my wife's mobility scooter and I am hoping to tap your expertise.

Background
==========

My wife has a mobility scooter which has two 82Ah Haze SLA (AGM) Batteries, which we recently replaced, along with a new (matching) charger. The batteries are connected in series to provide 24v.

My wife is a "big girl" but her weight is well within the capacity rating of the scooter. Unfortunately we live halfway up a steep hill.

Normal (daily) usage is a leisurely trip to the bottom of the hill and back home. This takes about 2 hours and covers about 3 miles. When the scooter is not in use it is permanently keep on charge.

Finally, we have been told that when going down hill the auto brake put the excess power back into the battery.

Environment
===========

I don't know how much this effects things but I'll list it anyway:

- We live in a hot country. Average maximum summer temperature is upper 80s F and average maximum winter temperature is lower 70s F.

- There is an all-year wind which blows light sand everywhere.

The Problem
===========

When new the batteries handled the daily trip with no problems. however, after about three months they started playing up on the hill just before home.

Specifically, the battery low light flashes and the scooter barely makes it up the sloop.

Originally I believe that this is some kind of power problem and not a capacity problem as:

- once the scooter is back on the flat it works normally.

- the battery indicator goes back to full.

However, after 4a I am not sure.

Measurements
============

I have taken the following measurements (individually on both batteries):

1. Fully Charged: 13.75

2. After 24 hours: 13.25

3. After a short (1 mile down and up the hill) and 1 week: 12.95

4. After normal morning run 12.91
- across both batteries 25.6

4a. After 4, I went further up the hill[1,2] and back
(about a mile) 12.8/12.5
- across both batteries 25.3

[1] I am half the weight of the wife.
[2] Even with me on, the scooter struggled with the hill.
Just to double check, I recharged the battery and tried
the hill again, it went up fine.

Questions
=========

Can anyone tell me why a new battery works fine but seems to lose power/capacity after a few month.

Also, does anyone know anyway I can refresh the battery or, worse case, is there a different type of battery I can try. I thought about using Gel batteries but understand they don't like heat.

GregsGarage
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Re: Help Needed with Mobility Scooter Batteries

Postby GregsGarage » Sat Jan 19, 2013 6:20 pm

I can think of 2 possible causes for the short battery life.

The number of charge-discharge cycles a battery can do will depend on how deeply it is being discharged. For example with a 100% discharge the battery may only last a 100 cycles but a 50% discharge may give you 400 cycles (I've just pulled these numbers out of thin air, hopefully your battery manufacturer can provide an expected life vs depth of discharge graph). If your daily usage is always running the batteries all the way down your battery life will be short. Another thing to watch out for is the claimed capacity. You need to find out what the capacity is for the discharge rate your scooter uses. Most likely the 82ah is for a constant 20 hour discharge (that is the battery should be able to deliver 4.1 amps for 20 hours). The problem is your scooter doesn't discharge like this. It will discharge the battery at a much higher rate. The effect is that the actual capacity will be much smaller, maybe only 40-50ah, not the claimed 82ah. A good example can be found in this spec sheet from secbattery.com. This is the type of information you need to find the best battery for your application. I wouldn't rule out gel cells on temperature concerns. So your short battery life could be as simple as discharging the batteries to far.

But another possibility comes to mind, you stated that the scooter can recover energy when going downhill. The problem you have is that since you are starting out at the top of a hill with a fully charged battery you won't be able to put any more energy into the pack, or at least you shouldn't try. But it is possible that the controller is putting energy into the fully charged pack anyway. Overcharging batteries will greatly shorten their life. This could be checked quite easily with a voltmeter. Before starting out from home with a fully charged pack take a volt reading of the pack. Drive down hill, stop at the bottom, switch off the scooter take another reading and if it is higher than when you left you have a problem. Even better, if you can find a safe way to do this safely, would be to attach the voltmeter to the scooter and get live readings. If the voltage goes up on a fully charged pack, then you have a problem.
Greg Fordyce

Daewoo Matiz
http://www.evalbum.com/4191

ghostcat
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Re: Help Needed with Mobility Scooter Batteries

Postby ghostcat » Sun Jan 27, 2013 12:46 pm

GregsGarage wrote:But another possibility comes to mind, you stated that the scooter can recover energy when going downhill. The problem you have is that since you are starting out at the top of a hill with a fully charged battery you won't be able to put any more energy into the pack, or at least you shouldn't try. But it is possible that the controller is putting energy into the fully charged pack anyway. Overcharging batteries will greatly shorten their life. This could be checked quite easily with a voltmeter. Before starting out from home with a fully charged pack take a volt reading of the pack. Drive down hill, stop at the bottom, switch off the scooter take another reading and if it is higher than when you left you have a problem. Even better, if you can find a safe way to do this safely, would be to attach the voltmeter to the scooter and get live readings. If the voltage goes up on a fully charged pack, then you have a problem.


Just got round to trying this test and not only are the batteries not been overcharged but they are actually been discharged. E.g.

Fully Charged: 13.9/13.9/27.9

At bottom of Hill: 13.1/13.1/26.0

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ChrisB
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Re: Help Needed with Mobility Scooter Batteries

Postby ChrisB » Sun Jan 27, 2013 5:08 pm

It would be interesting to know the discharge current during the hill climb part and for how long this hill is.

I know it sounds daft but check tyre presures, blow them up nice and hard, you can lose quite a bit if the tyres are a bit squashy.

Next make sure theres no drag on anything and everything spins freely.

Are those voltages that you are measuring on load volts or off load volts, I am suspecting they are off load volts which wont give a true figure really.

Being able to get a true idea of the load current (running current on the flat and the hill) will give you a good idea how well the batteries should perfom.
The 82Ah Haze units say they are C20 rating which means to get 82Ah out of them the max discharge is 4.1amps over 20hrs :? I suspect this is whats causing the problem, your exceeding the discharge rating and thus they are not delivering their capacity :?

You dont mention the actual run time, how long it takes, without the current drain and the run time its hard to say what the issue is but I suspect your discharging outside their spec and as greg mentions your taking them below their rated voltage on load.

Dunno if that helps or not

ChrisB
I reject reality and substitute my own !!!!!!

GregsGarage
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Re: Help Needed with Mobility Scooter Batteries

Postby GregsGarage » Sun Jan 27, 2013 9:04 pm

The no load readings are useful, I think we can rule out the scooter overcharging the cells while going down hill. I didn't think it was likely, but needed to be ruled out.

As Chris has said we need more information to go any further. I looked on the http://www.hazebattery.com/ website and down the left side they have links to data sheets for all their batteries. See if you can find the data sheet for your exact battery, then we can look at the specs. You will need to get the manufactures part number off the battery, I had a quick look but didn't see any 82ah batteries, lots of 80ah. Also while you are looking at the batteries, they should have a date code on them. See if you can find that as well, you don't want to find that your new batteries have been sitting in a warehouse for years before you bought them. The Haze data sheets did however give specs for higher discharge rates than the standard C20 rate.

As Chris has said you also need to know how hard and long the scooter is working the batteries. Something like the Xantrex link 10 meter (or equivalent) would be ideal for this, but they are pricey and the current shunt takes up quite a lot of space. The e-bike people might be able to recommend a meter for logging this type of data. I know that several different units are around but have no personal experience with them. Without knowing how much current the scooter draws going up hill it will be hard to choose a good battery.

One final thought comes to mind, many electric vehicles will specify a maximum incline that they are rated for. Does yours and are you within the ratings?
Greg Fordyce

Daewoo Matiz
http://www.evalbum.com/4191

ghostcat
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Re: Help Needed with Mobility Scooter Batteries

Postby ghostcat » Mon Jan 28, 2013 2:44 pm

OK. I need to work out how to measure the on-load current. I can also work out the slope, which will be easier. Current estimate is 200' in about 1500' but that is just a guess. I will get a more accurate reading shortly

Meanwhile, assuming that this is load is too large; is there another kind/ make of battery I can try which will handle a larger discharge rate?

Grumpy-b
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Re: Help Needed with Mobility Scooter Batteries

Postby Grumpy-b » Mon Jan 28, 2013 5:16 pm

To try and ensure this is really a battery problem, check the connections. There may be corrosion or poor contact bot the battery controller and motor end. Check all and clean the connections to the batteries, a good tool for cleaning battery posts/ connectios are scotchbrite / pan cleaners, or the foam pads coated with fine abrasive from a DIY store. They dont shed a lot of dust/ grit.
Also check the actual conections on the end of the cables. I have seen some really badly crimped terminals, causing all sorts of not expected problems. SInce you have recently had the batteries and charger changed, that doesnt mean there is not a problem.
What part of the country are you?
Good point with the tyre pressures.
Regards
Grumpy-b

GregsGarage
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Re: Help Needed with Mobility Scooter Batteries

Postby GregsGarage » Mon Jan 28, 2013 10:55 pm

ghostcat wrote:I can also work out the slope, which will be easier. Current estimate is 200' in about 1500' but that is just a guess. I will get a more accurate reading shortly


OS map should help, should be able to view something on the internet.

Good point about connections, also anything getting warm after a climb would indicate a problem, just don't burn yourself by grabbing a cable to see if it's hot. :shock:
Greg Fordyce

Daewoo Matiz
http://www.evalbum.com/4191

ghostcat
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Re: Help Needed with Mobility Scooter Batteries

Postby ghostcat » Sun Feb 03, 2013 12:49 pm

Thanks for all the replies so far, there have been some good points.

I did think about bad connections and so I took some measurements at the plugs that are used to connect the battery to the scooter. These were the same as the ones from the battery terminal. Just in case I have measured the resistance between the battery terminal and the lead and they are all around 1.7 ohms.

As to where I live, I don't live in the UK. I am actual in the Canary Islands, which is part of the problem as I don't have access to a dealer network like I would in the UK.

I have made a better measurement of the hill and it is 75' in 1200'. Not has steep has I originally estimated but still quite a slog.

I have tried to measure the current but think I have failed miserably. I only have a cheap multimeter with a 10 Amp range. On this range the scooter seems to use about 14 Amps on the flat and 17 Amps on the hill. Not sure how reliable this is given its a 10 Amp meter.

The battery Code No is "HZB-EV12-80" and, according to the label, has the following characteristics:

- Ttorque = 5-7Nm
- C5hr = 68Ah
- C20hr = 82Ah
- CCAsae = 483Amps
- MCAsae = 664Amps
- Vcyclic = 2.35-2.4vpc
- Temp = 20-25C

I still think the most likely problem is overloading the battery, although it could be operating outside the Temperature range. Before now I didn't actually know that batteries have a maximum discharge rate.

So assuming we are drawing more current than the battery is rated for, is there anyway of recovering it. Alternatively, is there a different type of battery that would provide a larger current

GregsGarage
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Re: Help Needed with Mobility Scooter Batteries

Postby GregsGarage » Tue Feb 05, 2013 12:28 pm

ghostcat wrote:I have tried to measure the current but think I have failed miserably. I only have a cheap multimeter with a 10 Amp range. On this range the scooter seems to use about 14 Amps on the flat and 17 Amps on the hill. Not sure how reliable this is given its a 10 Amp meter.

I wouldn't trust those readings at all, If the meter was properly hooked up for current reading it should have blown it's internal fuse, scary, don't use that meter for current measurements. Ask around and see if anyone has an inductive clamp on meter you could borrow. A motor mechanic might have one, or an electrician, but you need one that can measure DC current, a lot only measure AC current and will be useless for you. Failing that you need to put a current shunt in series with the batteries. Then you use your voltmeter on the millivolt scale and convert the value.

The battery Code No is "HZB-EV12-80" and, according to the label, has the following characteristics:
- C5hr = 68Ah
- C20hr = 82Ah

This is the most important info, data sheet for the battery can be found here. From the data sheet we can see that the C3 = 62Ah and C1 = 51Ah. Also on the data sheet is reserve capacity in minutes for a given discharge rate, which is the same info but looking at it a different way. So you need to work out what your discharge rate is on the flat and up hill, how long each discharge is and then you can work out how many amp hour you are using. You can then look for a battery that can handle this, preferably to a 50% discharge. Look at the bottom of the sheet for figures on cycles at varying depth of discharge.


I still think the most likely problem is overloading the battery, although it could be operating outside the Temperature range. Before now I didn't actually know that batteries have a maximum discharge rate.

So assuming we are drawing more current than the battery is rated for, is there anyway of recovering it. Alternatively, is there a different type of battery that would provide a larger current

Gel batteries may suit you better, look at the haze HZY-EV12-80, although it has slightly less capacity, it has far better cycle life. http://www.hazebattery.com/EVAGM/page2.htm

Once you work out how much energy you require for your journey you can then choose a battery that can handle it.
Greg Fordyce

Daewoo Matiz
http://www.evalbum.com/4191


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