Do replacing SAFT batts work ?

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Grumpy-b
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Re: Do replacing SAFT batts work ?

Postby Grumpy-b » Fri Jan 21, 2011 9:33 pm

Thinking about this I have had some cells that I have replaced also go again. I think that these were caused by the cells having been siting for a while, and oncei n the van having to go straight into action to get me home before charging. I have a cell down in one of my 11 packs, so I am going to precharge the replacement cell in the hope that may limit any damage. This is especially an issue in the cold weather. One problem is that you have to have the Batteries part discharged to show up the duff cell. The best solution would be to do the replacement, and charge before actually using the vehicle, then the cell would be unstressed when put back into use.Before taking batteries out of a vehicle permanently I usually do a maintenance charge and water them, so at least when they go back into another vehicle they have the best possible chance of being OK.
When one cell is going it has to put greater demands on the rest so its not surprising that others could follow suit.

All food for thought.

Grumpy-b

arsharpe
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Re: Do replacing SAFT batts work ?

Postby arsharpe » Fri Jan 21, 2011 9:50 pm

Hi Grump-b,

I am interested in how the other cells are stressed more. I can understand if the cells are parallel, but these are in series and getting low energy light earlier means that the other cells are not discharged so much.

Rob

Grumpy-b
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Re: Do replacing SAFT batts work ?

Postby Grumpy-b » Sat Jan 22, 2011 10:21 am

Through the whole chain the cells will be trying to deliver a certain amperage and pack voltage if the voltage is down then to deliver the power needed if we pesist in pushing the vehicle then increased amperage draw will take place. Hence the berlingos way of limiting this situation when the voltage dips below the threshold and the eco light come on. The controller limits the current draw. If you put in a new cell that cant deliver, then firstly is is being expected to pass higher currents and so could get internal shorting from that, and if the voltage of the pack is even lower because the cell is discharged, then we are back to higher current draw, except that since you will have had the pack disconnected the controller will have been re-set. So allowing full current draw until the threshold voltage is hit and the limiter cuts in. So if you replace a cell thats low on power itself it is both open to early damage and by virtue of having low voltage puts extra cutrrent load on the remainder. Until it is charged/ balance charged.

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ChrisB
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Re: Do replacing SAFT batts work ?

Postby ChrisB » Sat Jan 22, 2011 10:25 am

Grumpy-b wrote:Thinking about this I have had some cells that I have replaced also go again. I think that these were caused by the cells having been siting for a while, and oncei n the van having to go straight into action to get me home before charging...........


I think your suppose to do an initialisation on the pack if you ever change a battery but personally I think thats far to harsh a charge for old cells.

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Re: Do replacing SAFT batts work ?

Postby ChrisB » Sat Jan 22, 2011 10:44 am

Grumpy-b wrote:Through the whole chain the cells will be trying to deliver a certain amperage and pack voltage if the voltage is down then to deliver the power needed if we pesist in pushing the vehicle then increased amperage draw will take place. Hence the berlingos way of limiting this situation when the voltage dips below the threshold and the eco light come on. The controller limits the current draw. If you put in a new cell that cant deliver, then firstly is is being expected to pass higher currents and so could get internal shorting from that, and if the voltage of the pack is even lower because the cell is discharged, then we are back to higher current draw, except that since you will have had the pack disconnected the controller will have been re-set. So allowing full current draw until the threshold voltage is hit and the limiter cuts in. So if you replace a cell thats low on power itself it is both open to early damage and by virtue of having low voltage puts extra cutrrent load on the remainder. Until it is charged/ balance charged.

Grumpy-b


Surely current remains the same through out a series circuit though :? ohms law and all that.

As the voltage falls so does the current, again ohms law ?

Yes the battery thats failing will be put under more stress itself because its own voltage will be low and in some cases of real abuse can go reverse polarity, however I'm not sure it can make any difference to good cells, in fact I would think theres more chance that a cell thats failing and if it was to go high resistance its more likely to save other batteries due to it now limiting the current through the string.
If it fails short circuit then you've lost that batteries voltage in the string and thus ohms law dictates with lower voltage comes a lower output (working on a fixed load) and again a lower current flow through the rest of the string or exactly the same depending on what the controller is asking for.

A new cell will deliver the same current as all the rest of the batteries in the string, the problem stems from the fact it will likely to run out of capacity and thus voltage before the rest of the batteries if the capacity of the cell is unknown and so putting a new/2nd hand cell into a pack of batteries that isnt matched capacity wise is why you can run into problems with that cell later on and why they suggest you carry out an initialisation charge if you ever change a battery to ensure that the whole pack is at the same capacity, although as before I personally think its a very aggresive charge and not recomended on old batteries.

My understanding of the eco mode is to protect cells/batteries from their voltage diving too low or them going reverse polarity as in this situation the cells start to consume water at a vast rate and thus will dry out far sooner than others around them and mess the Ah overcharge water consumption reading up, these cells will now require watering far sooner than when the light comes on, hence why we try to water the packs far earlier than the recomended times i.e when the light comes on, and also why its never recomended to drive any real distance with the eco/recharge light on.

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Peter Eggleston
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Re: Do replacing SAFT batts work ?

Postby Peter Eggleston » Sat Jan 22, 2011 6:06 pm

I have found that if the voltage of one battery in a series string goes low because it is failing, it will quickly pull down the voltage of the whole string. It is much better to just bypass the ailing battery. Although I do not know how easily this could be done on a Bingo.
Peter

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ChrisB
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Re: Do replacing SAFT batts work ?

Postby ChrisB » Sun Jan 23, 2011 10:33 am

Peter Eggleston wrote:I have found that if the voltage of one battery in a series string goes low because it is failing, it will quickly pull down the voltage of the whole string. It is much better to just bypass the ailing battery. Although I do not know how easily this could be done on a Bingo.
Peter


I know what you mean but thats generally due to the battery going high resistance, if you were to measure the individual cells rather than the whole string I think you'd find the cells which are good will be fine, but the total output voltage will be lower due to the high or higher internal resistance of the failing cell, by shorting the cell you remove this resistance and thus improve the output voltage.

I still cant see how a sick battery in a series string can have any detrimental effect on batteries around it, and will only show up as a lower output voltage and reduced capacity on the whole pack.

With Berlingo batts these can end up going short circuit, which is handy as it saves having to short them 8) , I found this out on my old pack where I had several batteries like this and it appeared that while it reduced my top speed the underlying trend seemed that the eco/recharge light would come on and limit my top speed, but I would drive like that for miles and miles, because I still had capacity in the rest of pack it was just the voltage was low and thus tripping the limiter.
The new pack thats in it currently dies very quickly after the limiter kicks in, I have only about 2 or 3 miles before the van will just stop and go no where not even a crawl :shock:
This I put down to the fact all or most of the batteries have run out of capacity at the same time i.e the pack if very well balanced, rather than just one or two sickly battery causing the limiter to kick in and the rest still having plenty of capacity left.

I would say I have only done this twice due to a incorrect range estimation :oops: but not bad in the three or so years of ownership.

Interesting subject

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Grumpy-b
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Re: Do replacing SAFT batts work ?

Postby Grumpy-b » Sun Jan 23, 2011 2:37 pm

When you are trying to get a certain amount of power, the controller increases the current draw as the system pack voltage goes down. W=V x A
On the berlingo this is evident as the pack discharges you will have to drift higher into the amber of the Ecometer whereas when fully charged you may be able to stay in the Green band.
So if you have the Amber light come on and cut the available current draw down, which is what takes place, then thats quite a safe situation. If you change one of the cells at this point, the system will re-set and no limit.
If you put an low charged cell in the string, a higher current could be drawn to deliver a given power , and since the limit has been reset it could do it for a short while. If a cell in the string is a bit dodgy then this current increase could be enough to see it off.
For me I have to replace cells about 6 miles away with a significant hill at the end. SO before it gets charged its having to do quite a lot. I also normally change cells when the system is partially discharged so that I can see the failing cells. I have a number of cells that look OK when charged, even when loaded, but fail when partially discharged. Quite hard to spot these in a well charged pack.
I dont have a battery tester, so I use my volt meter and a 12v starter motor, this causes a useful drain on a cell and you can readily see the voltage drop and recovery rate. Simple and effective.
So thats my reasoning to to replace a duff cell with another that has a good amount of charge in it. Anything to help limit any damaging effects to my battery pack.
All of my spare cells are Maintenance charged before removal, so they do have electrolyte on board, but they also seem to self discharge over time. Thats expected.
Re Chris and his pack soon losing power once the light comes on. This is a feature of the limiter and seems to have changed depending on which controller version you have. My Van has an older controller that does exactly as Chris' possibly even sooner. The evlite shows the increased current limiting, but the later controller in my Multispace limits the current but does not increase the limit amount so whilst it reduces the power available overall it does not bring you to an early halt as with my van.
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ChrisB
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Re: Do replacing SAFT batts work ?

Postby ChrisB » Sun Jan 23, 2011 8:20 pm

Grumpy-b wrote: Re Chris and his pack soon losing power once the light comes on. This is a feature of the limiter and seems to have changed depending on which controller version you have. My Van has an older controller that does exactly as Chris' possibly even sooner. The evlite shows the increased current limiting, but the later controller in my Multispace limits the current but does not increase the limit amount so whilst it reduces the power available overall it does not bring you to an early halt as with my van.
Grumpy-b


But my controller has stayed the same through out :? I only changed the batteries :?

With the old set of batteries I could drive for miles, 12-15 miles wasnt un-common with the eco light glowing quite happliy the van would go right down to a crawel, yet it would still drive.

I drove it like that for a while with it limiting after just 5-10 miles, it would then just get slower and slower over the next 12-15 miles but you could drive it, eventually one of the front batteries went bang and it was at this stage I got hold of a spare one to swap it out, carried out an initalisation charge and promtly melted 30% of the rest of the pack :cry:
Thus a new (2nd hand) pack was sourced and fitted, this was charged normally and then taken for a few short runs before a maint charge was carried out, then I after a few cycles I carried out a range test and this was when I discovered the fact the eco light and limiting would come on and I would only have a few miles before it would stop dead, as I mentioned this has happened now a couple more times due to me getting the distance wrong and on every occasion its done just a few miles before giving up totally.

The controller hasnt changed at all :? , its the same controller that allowed me to travel many miles with the eco light and limiter on with a duff pack of batteries and now it travels just a few miles with a good pack, which is why I deduced that its due to the whole pack giving up rather than the controller doing anything different as I havent done anything to the controller :?

Re: Voltage/current side of things, surely the only reason the current appears to go up is because your running out of voltage, thus you have to apply more throttle to get the same speed, if you fixed the discharge then the current would drop in line with the voltage, I dont think its the controller doing anything its the driver.
I'm still not seeing how a duff battery in a string can effect other good batteries, the only possible issue is the driver trying to extract the same speed from the vehicle with a lower battery voltage but it cant happen due to the lower voltage, its got me quite interested in all this and I can see I'm going to have to dig my ammeter & voltmeter out and hook them up and take some real time measurements to see whats actually happening 8)

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harry morris
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Re: Do replacing SAFT batts work ?

Postby harry morris » Sun Jan 23, 2011 8:57 pm

Phew now then gentlemen this seems to be getting pretty involved, now then I have a really nice 2001 blingo with battery probs it will do 4 miles before the eco light comes on and the power starts falling down to a crawl but it gets me home! I have another van with ALL its batteries in the back of the vehicle also a 2001 vehicle, this vehicle is destined for new battery technology so I have no intensions of putting the batteries back in this vehicle, all the cells are 2001/some good some not so good, I want to charge the 6 volt cells individually and then load test them before putting them into the van with the battery probs, only one snag don't seem to be able to find a charger suitable for NiCads??? cheers HARRY MORRIS


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