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charging SLAs
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Glen
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charging SLAs

just read all the notes on NIMH Nicad charging and was wondering what is the key to keeping my SLAs in healty condition?

is charging them faster better than slower etc?
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Post Sat Jul 31, 2004 10:40 am 
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Spockie-Tech
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This depends on the manufacturing technique used for the SLA. There are Gel-Cell, Starved-Electrolyte and AGM (Absorbed Glass Mat) types which all have different requirements in terms of their optimum charging technique.

It seems the AGM batteries are the best for our application, since the fibreglass-mat seperators not only give the cell very high peak current capabilities, but also offer good resistance to mechanical shock (the mats stop the plates from touching and shorting when bent under impacts), as well as not having any limitations on "charge inrush current", unlike other technologies.

Apparently Gel and Starved-Electrolyte batteries dont like having big gushes of current poured into them when they are nearly totally flat and are then connected to a big beefy power supply that can supply 10 amps+ of current.

The current inrush does something nasty to the electrolyte or the plates (I forget which), so a lot of "Gel-Cell" chargers have what they call a CC/CV charging technique, where the charger starts off operating in a constant-current (CC) mode, where the maximum current that the battery is allowed to absorb is limited, until the charge state builds, then the charger switches over to a CV (Constant Voltage) mode to finish it off.

Absorbed-Glass-Mat batteries supposedly have no such limitations due to the increased surface-area of their electrolyte-soaked mats (the same surface area that gives them a higher peak output current than gel-cells) allowing them to soak up current as fast as your charger can feed it to them. So it is acceptable to run an AGM battery on a simple high-power constant-voltage (regulated) charger with no current limiting circuitry.

The actual charging voltage (when in CV mode) can vary in steps as well with some chargers. Initially, 14.4volts can be used to speed up the bulk of the current getting into the cell, then some back it off to 14.0-14.2v after a bit as the battery approaches full, and finally, if the battery is going to be left on "float charge" (where its basically 90%+ full, but you want to keep it "topped up") then the float-voltage should not be higher than 13.8v.

As I have mentioned before, one of the most important things an SLA charger needs to have is a smooth regulated output, something that 90% of them do not have (because its expensive to do at high currents). An output filtering capacitor big enough to smooth a 10amp supply can cost $50 all by itself, and thats without regulators and so on. If your battery charger isnt "rectified, filtered and regulated" then I wouldnt think about using it to charge SLA batteries.

Theres an awful lot of hype, marketing and wank in the battery charger market with "intelligent pulse controlled double overhead burp charging zap algorithims that revive tired batteries" and stuff like that used to sell chargers to the uninformed public, but your best bet is to check out the battery manufacturers spec sheets on what they advise and ignore the wank from the charger merchants. The battery manufacturers want their batteries to have better life and capacity than the competitions, so you can bet if there was some advantage to be had by charging their batteries in some "special" way, they would be telling everyone about it.

have a look at http://www.rcbatteryclinic.com/burp.html or google for "burp charging" for examples of the sort of bull that is out there for the unwary.

I hope all that covered your question glen.. Laughing short answer. if its a gel-cell, charge it slow, if its an AGM you can fast-charge it. in both cases, use a quality regulated charger if you want maximum life from them.

Post Sat Jul 31, 2004 12:52 pm 
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Glen
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i always love reading those massive responses Very Happy

well i believe you said that the supercheap batteries where just standard gell cells. i charged them with the beehive more often than not and had about 4 of them just stop working totally.

interesting thing is that with my CC 1amp powertech charger it seems to flicker between fast and slow charge really quickly when they are dead.

the new jaycar ones ive gotten are alot better, after about 5 fights no negative effects are showing (as opposed to the super cheap ones that died after 2 or so events) and thats after andrew has dropped them onto the concrete and all hehe so im guessing that they are the AGM.

that rcbattery clinic is a good site to may i add,

oh wait brett just for you -

i always love reading those massive responses Very Happy well i believe you said that the supercheap batteries where just standard gell cells. i charged them with the beehive more often than not and had about 4 of them just stop working totally.interesting thing is that with my CC 1amp powertech charger it seems to flicker between fast and slow charge really quickly when they are dead.
the new jaycar ones ive gotten are alot better, after about 5 fights no negative effects are showing (as opposed to the super cheap ones that died after 2 or so events) and thats after andrew has dropped them onto the concrete and all hehe so im guessing that they are the AGM.
that rcbattery clinic is a good site to may i add,

Laughing Razz
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Post Sat Jul 31, 2004 1:29 pm 
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Knightrous
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Just a quick question Glen, have all the supercheap SLA's that have died, did you always run them in series? I'm just wondering because Andrew and I were talking about batteries and he told me about what happens to some batteries in series, like on a primemover truck, where they need 24v, when there batteries go flat, some times they reverse pole. I was just thinking your dead batteries might have done that since you were always a 24v user.

Have you tried putting them on the charger in reverse polarity to see if they will charge? (Note: Only do this if your charger is polarity protected and if you really don't care about the batteries or the results of doing so Confused )

Someone correct me if anything I've stated is wrong.
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Post Sat Jul 31, 2004 3:15 pm 
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Glen
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yes they have all been in series,

as luck would have it me and jeff where talking about it today too, i want to get the battery back of andrew so i can put a multi meter in there and see if its reversed polarity in one of the cells.
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Post Sat Jul 31, 2004 3:41 pm 
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Totaly_Recycled
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Glen after reading all the posts ect here is my advice.
Bret has some good advise also ..
But the main thing to keep in mind with any type of lead acid battery is that you should charge it up as soon as its going flat goes flat .. dont leave it to tommorow .. the lead sulphide crystals (is that the right spelling) start to grow on the plates and harden then the battery wont take a full charge after that. If you
leave a brand new battery flat for a week and try to re charge it its almost imposible even if you do get it acepting a charge again it will never be the same as a new one ...
So the motto is charge it as soon as posible preferably let it cool first .. and dont exceed the batteries charging voltage.

The best way to chage a lead acid is on trickle or so i have read but
like Brett said most lead acids and glass type sla batteries will take all you can throw at them current wise until theyare about 90 percent full then the terminal voltage will start to climb rapidly and thats when you slow the charge rate down .

At the NSW event i didnt bother takeing the 7 amp sla out of Anhilation as it was too much hassle it had one 2.4 amp charger,2X4 amp chargers ,one 6 amp unregulated charger and a 5 amp charger all going in to it at the same time until the multi meter reached 13.5 volts then i just left one 4 amp regulated charger on to top it off.
I was charging the 7 amp Doss sla back to 90 percent in about 9 to 12 minutes (with out geting it hot )depending on how far Aaron had drained it.

Iff you are runing your batteries in series it is better to charge them in paralel at 12 volts. Even better is to charge every cell at 2.3 volts per cell ... but the way manufactures build bateries these days its imposible to do that .All the olden day batteries had external interconecters .

Just my two bobs worth ..

Post Sat Jul 31, 2004 4:31 pm 
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timmeh
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On my triton when selecting the battery capacity i have the option of 2amp or 2.5 amp i have a 2.2amp battery can i tell the charger to stop charging when it reaches 2.5 amp will it be safe as if i tell it to stop at 2amp i cant fully charge the battery
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Post Fri Aug 27, 2004 6:26 pm 
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Philip
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Your battery might be a 2.2 Amp hour battery. This does not affect charging current.

Post Sat Aug 28, 2004 6:43 am 
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timmeh
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Its not the chargeing current its the peak capacity setting so the charger knows what the capacity of the batery is
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Post Sat Aug 28, 2004 12:32 pm 
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andrew



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Hello all,

After a few testings of the weopon system (not hitting anything yet though Sad ) i checked the batteries after the sparking when the weopon fired up seem larger than normal and each sla battery (jaycar 4 amp good quality one). Each battery for around 15.5 ish volts. I am not sure why this is occuring but i threw the jaycar charger onto it and its charging and doesnt read green light (finished).

I need to know whether i did something wrong here. If the batteries are busted, if anybody else has had this problem or if theres a way i can fix it because i wouldnt mind 30 volts in the weopon but the drive will blow big time and maybe the speed controllers too (drill triggers).
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Post Sun Oct 03, 2004 8:18 am 
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timmeh
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Thats happened to me a few times with sla's the fully charged light has never turned on with 2 chargers iv had not incl my triton i dont know why this is eather?
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Post Sun Oct 03, 2004 6:40 pm 
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Glen
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question -

is there a way to figure out the capacity of a battery (SLA). i know the triton can work it out itself, so my question is can i work out the capacity via some formula/equation/whatever.

and also my batteries will not charge to a full 13v+ on somedays (usually will only get to 12.7), yet on others it will go all the way to 13.2v, any ideas why it happens and how i can get them to go to 13+v and stay there?
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Post Tue Oct 12, 2004 8:00 pm 
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Valen
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only way to work out the capacity of the cell realisticly is to either go with the manufacturers number or to measure it (which is what the triton would do)

measuring is done by seeing how many amps for how long you can pull out of the thing
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Post Tue Oct 12, 2004 8:04 pm 
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timmeh
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I was discharging a 12amp hawker at 1.6amps and after about 3 amps had been disharged i felt the triton and it was hot enoughf to burn me!

Is that normal Sad
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Post Sat Nov 27, 2004 2:47 pm 
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Spockie-Tech
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12v * 1.6 amps = about 20 watts of heat.. thats a fair bit, but the triton should cope with it. Is the Fan working ?

The approximate rule of thumb with electronics is the 10-second-thumb test. If you cant leave your finger/thumb on it for 10 seconds without going ouch, its probably too hot..
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Post Sat Nov 27, 2004 5:52 pm 
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