Battery Vehicle Society

After only 11 months and 1300 miles my four Haze 110ah agm lead acids are begining to fail. Range was about 45 miles now 25ish. This is very disappointing as I have treated them well, never discharging them more than 25% except once at 50%. The maximum discharge current is 100 amps, and I only go above 50 amps for seconds.
After 48 hours rest the voltage of each battery is approx. 12.95v.
I always charge as soon as possible after driving.
Could the problem be with the way I am charging them? do they need a long float charge?
They are individually charged with Numax 10 amp units [described as 4 stage intellegent chargers], are these any good?
Unless I can inprove the battery life, my 48v City-el will remain uneconomic.
Help needed please.

Sadly this is the problem with any battery particulary when used in EV's, discharging them outside their spec.

Looking at this spec sheet http://www.easystartbatteries.co.uk/doc ... 12-110.pdf it gives discharge specs to C5 only, @ 88ah, thus the rated output current is 17.5amps over 5hrs and I suspect your taking way more than that out of them in a much shorter time and it is this which is killing off the cells and which generally does kill off batteries seemingly early.

Generally EV's will discharge battery at the C1 rate or higher, even the Berlingo can push the envelope of the Saft cells with its discharge curve, the best vehicle I've ever owned that kept the discharge within the battery spec was my old Bedford CF electric, that had 205ah batteries @ C5 these would give 41amps for 5hrs and the vehicle would generally draw that best part of the time due to it having a nice high voltage and thus the batteries would last a real long time, I dug one out of a field and still managed to get a range of 30 miles from them after some tickling to bring them back. They were just never worked hard you see.

Sadly theres not a lot you can do apart from look for a set of batteries which will quote you a 1hr discharge rate and theres not many that will

Or move to Li-ion

ChrisB

Even with the large prismatic lithium cells (hipower, thundersky, CALB, etc.) you should aim to keep average discharge below 1C for long cell life. Probably around 0.5C if you can manage it. I have talked to someone who tried to run thunderskys well above 1C and only got 300 miles from them. My Hipower pack is doing well in my Matiz so far. Since May I have over 2000 miles, and the pack is doing quite well. The large Headway cells like the 16ah 40160 cell look promising for smaller packs run above 1C, but time will tell.

I have the haze agm spec. sheet in front of me, the one hour capacity is 66ahs.
The maximum charge current is 21.4amps, does this sugest that the maximum discharge current should also be 21.4 amps?
My chargers do not have temperature compensation,could this reduce battery life?
My chargers may not have the correct charge profile, could this reduce battery life?

I've now found the correct spec sheet like yours........
http://www.hazebatteryusa.com/s.nl/sc.15/.f
........and they do spec the C1 rate at 66ah so in theory you should be able to take 66amps for 1 hour from them.

They do mention optimum charging on the sheet.



Certainly if your chargers are taking the charge voltage above 14.46 volts (as it does say this is the max) then you will be doing damage to them.

AGM's do require to be generally charged fairly carefully so not to gass them to hard.

ChrisB

I have just finished charging my batteries after a 9 mile trip.
My numax chargers apear to increase their output voltage as the battery voltage
increases. I don't know what the maximum was as I missed it
This doe's not look like the constant current constant voltage method to me.
What effect this all has on battery life I have not a clue
After 8 miles when my ammeter reads 50 amps the batteries show 45v, a few weeks
ago they were 46v. In your experience would you therefore think the range has droped
by 20%, 25%, 30% or what

All chargers will increase voltage as the battery voltage rises, the key is when it stops.

The effect of over volting AGM's is they will gas and not have time to recombine and so the vents will release the gas and thus the cells will end up drying up and will reduce the capacity early.



Very hard to say without carrying out a static discharge on the battery and actually seeing what the battery capacity stands at .

ChrisB

It is now one year and a further 1,200 miles since I wrote about the apparently failing batteries in my city-el vehicle.
During the past year the batteries stopped deteriorating which surprised me, I put this down to my ammeter not being all that accurate and also lower battery temperature having a much greater affect on voltage drop under load than I allowed for.
12 days ago after 15 miles hilly driving the battery cut-off switch which I had fitted about a year or so ago failed, no doubt due to the high current. After bi-passing the switch I discovered that the voltage sag under load was much less, in fact the batteries appear as new!
I now realize that this switch must have been creating a resistance and therefore a voltage drop, I remember that it used to get a bit hot, but at the time I thought no more of it.
I am now in the process of building four led bar graph volt meters so I can monitor each of my batteries as I drive.

Like one of these? http://www.evconvert.com/article/led-bargraph-battery-monitor-part-2

I have 5-segment LED bar meters for each 12v battery in my EV - they are very useful for looking at the voltage sag while you are actually driving, so you can see if any one battery is weaker than the others.
I did not know how to make them, but bought them off the shelf from 4QD - they call them "battery condition meters".