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See! I told you I would need guidance!

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New Member
Some of you might remember 'Mr Nice Guy' from a week or two ago. Well I am here and need some advice.

I have revived an old fluorescent lantern, the tube driver circuit still works well so all I needed to do was fit new Battery (6V 4Ah, Sealed Lead acid type) and a charger circuit. I have thought about this and decided not to play around with circuits that pull back on the current at different states of charge and just throw a constant current at it and "let it decide itself" how much current it needs.

I have read up on suitable charger circuits here on the forum and plumped for THIS one, using the design with an L200 constant Current & Voltage regulator. I have built the circuit and set the output to 6.90V @ 1A. I have installed the Battery and Regulator. All seems fine and the light works from the battery :D I now intend to fit a full wave rectifier before this charger circuit which should allow a range of power sources (12-24V Approx AC or DC) to be plugged into the lamp in order to charge it.

My question is.... What the hell voltage should I be charging the battery at? Is the 6.90V correct or should I be opting for the cycle voltage of 7.2 - 7.5 Volts? I understand the difference between cycle and standby but I am only going to be using this lantern once every few months. and the lantern is only likely to get plugged in to charge a day or two before I am due to use it. Should I be charging the battery to the standby voltage when I get back from using the lamp and then just topping it back up to the standby voltage days before its needed again? Or should it be considered at cycle use and just wait till days before it's needed and whack it up to 7.5 volts days before its needed?

I hope you understand what I mean, I want to charge this is a way which is least likely to cause the battery any heartache!




If this is a lead-acid battery you don't need to worry about charge current or timing. Just apply about 7V and it will take as much current and time as it needs.

The current will automatically reduce as the battery charges up until it becomes a trickle.

Things were so much simpler before NiCd and NiMH were invented.


Well-Known Member
Most Helpful Member

Have a look at this link http://www.powerstream.com/SLA.htm

The problem with acid batteries, as I expect you may already know, they slowly self discharge.
If left off charge for a few months, the battery could discharge itself into a deep discharge condition, which is not good for the battery.
A point to remember is that the battery has a finite number of times it can be discharged and recharged before its starts to lose its storage capacity.

I charge my high power torch lead acid battery, when the light output falls off, I also so check it from time to time, by switching it on.
In your case, as you say, you know when you need it 2 or 3 days in advance.

I think I would look around for a an 'intelligent' charger design, for example, it monitors the state of the battery
and sets the charge voltage to suit.
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An LM317 circuit set at 7V should do the job, you can get the circuit from the datasheet.


New Member
OK thanks to all for your input, I have decided to stick with the design I have already made (The L200 constant current and voltage circuit) Just because it's already done and will work to a degree. I have now set the output voltage to 7.0V and I will make a point of checking it occasionally and topping it up once a month aproximately.

Thanks again!!!



However you can have a variable voltage regulator with an adjustable current limit.


New Member
What?? ehh??... lol... What a muppet.... Not constant current..... I have Limited the current!!!! fool! freak! what a plonker I am.

I mean I have built the L200 Circuit as mentioned above and set the output voltage to a fixed 7.0 volts, I have also LIMITED the current to 1 Amp since the battery has something along the lines of "Max initial current 1.2Amps" written on the side of it.

It's too late for this, I am away to bed lol.... I am knackered!
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