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SLA Battery Charging

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Nicko

Tue Apr 27 2010, 01:17PM

Registered Member #1334 Joined: Tue Feb 19 2008, 04:37PM
Location: Nr. London, UK
Posts: 615

DaJJHman wrote ...

And thanks for all of the replies! - I'll need a more proper, and compact, charger for the future and always wanted to build one rather than spend the money on one

This was pretty much my rationale too. You buy one, you are never quite sure of what you are getting, especially if it's some cheap junk from eBay or whatever, and you learn nothing... it also goes against the grain; if you can do it yourself, then do it. And learn about SLAs in the process.

Intelligent chargers are quite neat - originally I was going to do the whole thing with an AVR but ran out of time - using a uP would be ideal as it could be calibrated without having to use 1% resistors and would be easy to change for 1 or 2A max rate or pretty much any battery voltage. s/w is very much my strong point, so its definitely what I'll do for V2.

Using a dedicated analogue chip like the UC3906 is helpful and fast and the app notes were an education in themselves about the infinite subtleties of SLAs... Have a look at them...

If you want to be really cute, have a look at Atmel app note avr450

, though be warned that some on the AVRFreaks forum think the app note stinks....

Proud Mary

Tue Apr 27 2010, 02:23PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

I've always liked the versatile L200 currrent regulator, which can source variable constant currents of up to 2A with which just a few extra components. There are heaps of battery charger circuits which use it on the web.

Sulaiman

Tue Apr 27 2010, 05:04PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

I charge my VRLA (SLA) batteries using constant current then constant voltage,

In discussions with Yuasa engineers; a low charging current << C/10 is good - if you can wait.

I charge to and maintain at the 'float' voltage of 2.275 V per cell @ 20C -3mV/C
This voltage is VERY important for the life of the battery, as is temperature.

I prefer linear- (as opposed to switched-) mode because I don't want to hunt down rfi problems in other circuits and a linear system is much easier to maintain.
A simple temperature-compensated battery charger using a 317 is in this data sheet.

,C1,C1003,C1040,C1055,P2041

Carbon_Rod

Tue Apr 27 2010, 08:51PM

Registered Member #65 Joined: Thu Feb 09 2006, 06:43AM
Location:
Posts: 1155

Low Current regulated trickle chargers are kinder to the cells.

Most people don't even bother getting deep cycle rated cells anymore given the low replacement cost.
$16/10Ah is hard to beat...

Hon1nbo

Wed Jun 09 2010, 10:07PM

Registered Member #902 Joined: Sun Jul 15 2007, 08:17PM
Location: North Texas
Posts: 1040

ok, so I just got a 12V 92 Ah battery.

I want this battery to last, as I will likely never get one this cheap again. So I want to use a lower current, but not so low as to require a two day charge time (one day would be okay I guess if need be). Because I don't have time to build a charger, and I really want to be careful with this battery, I've opted to buy one. This would also be a better decision because this battery will have its own charger/maintainer, as it will be used under much different circumstances than my other batteries (I will still build a charger for my other batteries).

I usually go to Harbor Freight for inexpensive tools and parts, but I'm not sure if their stuff is up to the task of this size of a battery.

here's one

here's another

any thoughts? - I'm going to build a trickle charger using a solar panel to maintain charge, but I want something more for when I have drained the thing.

-Jimmy

Steve Conner

Thu Jun 10 2010, 09:09AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

What voltage was the battery charged to when you got it?

Hon1nbo

Thu Jun 10 2010, 04:13PM

Registered Member #902 Joined: Sun Jul 15 2007, 08:17PM
Location: North Texas
Posts: 1040

Steve McConner wrote ...

What voltage was the battery charged to when you got it?

it was charged to 12V already (though not a full charge obviously), I had enough juice in it to operate my HF for a little while without issue last night, why?

EDIT: I think this battery is going to stay in the car, but I'll be checking temperature regularly to make sure it's safe. If it does, I thought about using two methods: a Solar trickle charger as I'm not on my HF much, or using a cigarette socket charger to charge while I drive, but I cant find one like that.

Hon1nbo

Sat Jun 12 2010, 01:19AM

Registered Member #902 Joined: Sun Jul 15 2007, 08:17PM
Location: North Texas
Posts: 1040

as it turns out, West Mountain Radio makes exactly what I need, but it's $140! - I think I'll take the battery out for a little while when it needs a charge, but I am selling a lot of old gear so I might have enough extra without spending everything. This would make a nice dedicated charger for this battery only, I still plan to build one for my workbench!

-Jimmy

Conundrum

Sat Jun 12 2010, 11:18PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061

Steve McConner wrote ...

Proud Mary wrote ...

I like to charge just as slow as you please, so my sleep is not disturbed by gurgling electrolytes, hissing vents, and arcing between buckled plates.

My sleep was once disturbed by a huge explosion and clouds of foul-smelling steam.

I was charging a big Ni-Cd pack made of eight 4/3D cells, inside a metal box that I built for it. One of the cells overheated and bulged, and this caused the rest of the pack to get jammed hard against the box, damaging the insulation, shorting it and exploding several other cells.

If I remember right, I put the smouldering mess out on the window sill and went back to sleep.

rofl..

During my less wise days I once tried to charge a 14V drill pack (also sub C nicads) with what later turned out to be a particularly flaky SLA charger which decided to elevate its voltage off load to >20V.

Needless to say that drill pack disassembled itself with extreme prejudice all over my nice chair, desk etc.

the phrase "earth shattering kaboom" seemed appropriate, however you'd think the safety circuit would have shut the pack down...

Just had a near miss with one of those "thumbscrew" Hahmel chargers, which decided to blow one of my expensive (brand new) Li-Ion camera packs.
By the time I finally realised that it was charging for way too long, not only was the pack bulged by twice its thickness but was smoking hot to boot.
That went straight in a glass of bicarbonated water, outside to let it discharge itself under somewhat safe conditions.

you'd think that a >Â£40 charger would at least include a failsafe or two so that if the micro crashed the thing would shut down hard and stop charging, but no.
Do these people not know of the wise ways of the watchdog timer ?!

on the flip side, i have two 12V 4AH packs here which are "dead", they do charge but not for long.
terminal voltage is 1V, reckon they are totalled?

-A

Who now plays with LiFePO4 cells, at least they fail gracefully (loss of capacity with overcharging)

Hon1nbo

Sun Jun 13 2010, 04:43AM

Registered Member #902 Joined: Sun Jul 15 2007, 08:17PM
Location: North Texas
Posts: 1040

I sold enough things to have some extra cash for the West Mountain Radio Power Gate, which works with either a car or a power supply! - I hooked up the radio and battery, then realized I was one powerpole set short : - P
but it works so far, the electronics store is closed tomorrow so I'll go monday to pick up a pair and do a full test!

I also need to ground all of my equipment double, as it turns out when I use 40m my car resonates and my radio goes berserk and my Amber light-bar comes on! - I think my ground point might have a coating, sandpaper and powerpoles and my shack is complete!!

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