Watering SLAs?

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badnewswade
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Watering SLAs?

Postby badnewswade » Wed Mar 02, 2011 1:16 am

Hi folks - I've had my SLAs for a long time - one set I've had for a year and I've already watered, the other set I've had for almost two years and I've watered one of them - slow charging it now (with my nice new CTEK® charger). I plan to charge them all seperately then put them back in the bike one string at a time (this is my big 48v bike).

It occurs to me that it's really hard to tell how much to put in. The older set in particular is worrying as it has a sort of plastic thing below the caps, you can't see very much and it's really easy to end up with water coming out of the well. Should there be any / much water above this plastic thing? I'm terrified that I've made an awful mistake and am going to blow myself up with overwatered batts. Am I doing the right thing or should I just back away slowly from this whole project? Is it going to be safe to re-seal and carry on using these things?
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Jeremy
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Re: Watering SLAs?

Postby Jeremy » Wed Mar 02, 2011 7:35 am

It isn't normal practice to remove the sealed emergency over-pressure vents and try to add water to a sealed lead acid battery, primarily because there is no way of being able to mix added water to the fairly thick internal electrolyte gel - the water will just sit on top of it, diluting the top surface of the gel and probably make the battery work less effectively (the very top of the plates will be working with more dilute electrolyte, in effect).

The other problem with trying to do this is that, by opening the seals, you risk damage to the airtight seal needed to maintain the gel in its moist state, allowing it to dry out and the battery to fail prematurely.

These batteries are called sealed lead acid, and maintenance free, for a reason - they are meant to be left completely sealed for their entire life and not tampered with.

I know that people have come up with all sorts of schemes for supposedly restoring weak cells, or boosting power, by injecting liquids into SLAs, but I've not seen any evidence that they ever work - as far as I have seen these tricks always shorten the life of the battery.

Jeremy

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badnewswade
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Re: Watering SLAs?

Postby badnewswade » Wed Mar 02, 2011 10:58 am

Oh dear. But the literature I got with the batts (Noblift 28ah batteries from UK Eco scooters btw) did mention something about topping up electrolyte after a year?
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Jeremy
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Re: Watering SLAs?

Postby Jeremy » Wed Mar 02, 2011 11:33 am

It sounds as if these aren't SLAs, but ordinary wet cell low maintenance batteries, if the supplier recommends topping up.

The difference is that SLAs use a gel electrolyte and can't be topped up, whereas low maintenance batteries use an ordinary liquid electrolyte and can be topped up. The SLAs are completely sealed, except for the safety vents that can open if they are over-charged, and can be mounted upright or on their sides, whereas low maintenance batteries aren't totally sealed, they will have normal filler caps on each cell and are only really spill resistant; they have to be fitted upright like any other wet battery.

Normally you fill wet cells until the plates are just covered. Sometimes there will be a plastic bar or grill just below the filler and this usually marks the electrolyte level - in other words carefully fill until the electrolyte is just up to the bar or grill, not flowing out of the filler.

Jeremy

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hohisilver
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Re: Watering SLAs?

Postby hohisilver » Wed Mar 02, 2011 11:44 am

And don't check the level as a friend of mine once did, by sticking your finger in the cell! :lol:
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badnewswade
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Re: Watering SLAs?

Postby badnewswade » Wed Mar 02, 2011 12:18 pm

Heh. The top is sealed with glue and pops off easily, it has rubber caps but no valves. Holes are way too small to put fingers in though, I have to use pipettes to top it up. There is indeed a plastic thing below the filler, sort of like a plate with vague round indentations, the water does indeed come over the top of this after filling.

I'll post pics and you can decide... can't see inside it with my rubbish camera though.

Image
Image
Image

Anyone recognise the manufacturer?
34 Watt Hours per mile, or > 700 MPG. What, me, smug?

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badnewswade
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Re: Watering SLAs?

Postby badnewswade » Wed Mar 02, 2011 12:42 pm

On further inspection the round indent thingies are white in colour, while the rest of the plate is blue.
34 Watt Hours per mile, or > 700 MPG. What, me, smug?

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Jeremy
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Re: Watering SLAs?

Postby Jeremy » Wed Mar 02, 2011 1:05 pm

These are indeed wet maintenance free batteries, although the "sealed rechargeable battery" wording is a bit dubious, so I can see where the confusion arose.

I think just keeping the electrolyte level at the plastic thing is the right thing to do, although because they are maintenance free I'd have thought that they probably don't need watering very often, if at all.

It'd probably be a good idea to stick the caps back down with some silicone sealant when you've finished, to keep the cells reasonably well sealed. Maintenance free batteries use a chemistry that recombines the gas generated during charge to avoid the need for venting and topping up. If the lids aren't sealed then they'll need topping up more frequently, as it's inevitable that the gas will escape otherwise.

Jeremy

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badnewswade
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Re: Watering SLAs?

Postby badnewswade » Sun Mar 06, 2011 11:57 am

Aaaaargh!

Did as you said, then topped off electrolyte after charging each battery as some of it had boiled away. (I charged with the rubber tops off because when I put them on they popped out anyway)

Now they've all gone down to about 12.8 volts! Have I put in too much water and diluted the electrolyte, or is this just an artefact of the charger? (a Ctek xS 800) Do this type of battery need to be sealed to retain a complete charge?

The way I see it I have two choices: Float charge each one with the tops off until the excess electrolyte has boiled away, or seal 'em up, wire them to 48v and charge 'em with the moped charger. What should I do?

PS - the lids are rubber caps which are held in place by a top plate, which in turn is glued on. I've got a horrible feeling these are AGMs because the plastic thing feels more like a fibreglass matt (I tried to use a hydrometer on one of them with farcical, but non-disastrous results).

So whaddya say - Boil off the water or throw more volts at it?
34 Watt Hours per mile, or > 700 MPG. What, me, smug?

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ChrisB
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Re: Watering SLAs?

Postby ChrisB » Sun Mar 06, 2011 6:29 pm

12.8 volts sounds spot on for a LA at rest, if you ask me :?

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