Charging circuit for lead acid battery

Hi all,
I am still in the planning phase to build a charging circuit for lead acid battery, with an AC input voltage generated from AC dynamo like bicycle. The AC dynamo generates AC output using hydro turbines. Does the input AC voltage from a common bicycle dynamo sufficient to charge up a 12V/7AH lead acid battery? And what rectifier circuit should I use for the charging circuit?

Thank you.

hydro turbines are for water.
turbines

This would be more like it

Is it possible to attach turbines for the bicycle dynamo to generate AC? I am doing a flood warning sensor system where I will need the AC from dynamo to charge up a lead acid battery.

Yes not a problem

A common bicycle dynamo generates about 6volt AC if it spins fast (look at the voltage rating of the bulbs).
If you use a voltage doubler circuit, you 'might' have enough voltage to charge a 12volt battery.
Maybe better to use a lower voltage battery, e.g. a 6volt Lead/acid.

Capacity (size) depends on how much current your warning setup will use.
A "flood warning" system can sleep most of the time.
Rechargeable NiMh AA batteries could be enough.
Leo..

Like any permanent magnet alternator a bicycle alernmator generates a lot more than it'd nominal voltage with a low load.

I've made wind generators using old '6v' hub 'dynamos' with a bridge rectifier that would generate about 1/2 amp into a 12v battery in a decent wind (100rpm?)

Open circuit volts approached 20.

Allan.

Last time I played with a common one that runs against the tyre I wasn't so lucky.
They must have improved a lot.
Leo..

allanhurst:
Like any permanent magnet alternator a bicycle alernmator generates a lot more than it'd nominal voltage with a low load.

I've made wind generators using old '6v' hub 'dynamos' with a bridge rectifier that would generate about 1/2 amp into a 12v battery in a decent wind (100rpm?)

Open circuit volts approached 20.

Allan.

I second this. My bicycle generator (not even a hub type) reaches 40V when running without load. But given the power output of 3W it will take a long time to charge a battery of 7Ah.
Lead-acid batteries can easily be charged by just limiting the voltage to 14.4V. Use a bridge rectifier with Schottky-diodes and a simple low-drop 12V voltage regulator and "lift" the output voltage by connecting the ground pin to ground through 2 standard diodes

kurukuru1234:
Hi all,
I am still in the planning phase to build a charging circuit for lead acid battery, with an AC input voltage generated from AC dynamo like bicycle. The AC dynamo generates AC output using hydro turbines. Does the input AC voltage from a common bicycle dynamo sufficient to charge up a 12V/7AH lead acid battery? And what rectifier circuit should I use for the charging circuit?

Thank you.

First thing you need to learn is how to properly charge (and then float) a lead-acid battery.

Every battery type has it's own specific charging method, and not adhering to that method can lead to an undercharged battery, an overcharged and boiled out battery or even (in the case of lithium based secondary batteries) actual fire and explosion.

The worst you can do to a lead acid battery is overcharge it and boil away the electrolyte and/or warp or sulfate the plates. The battery will not explode like a lithium can.

You do, however, need to be aware that charging a lead acid battery releases hydrogen gas. You need to be sure the gas doesn't accumulate (like indoors). Hydrogen has a VERY wide explosive limit (anything between 4% and 75% mix with air is explosive).

Exploding hydrogen from a lead acid cell usually touches off the hydrogen INSIDE the battery as well, resulting in the top blowing off and sulfuric acid being sprayed all over the place.

Learn first, then build.

krupski:
Exploding hydrogen from a lead acid cell usually touches off the hydrogen INSIDE the battery as well, resulting in the top blowing off and sulfuric acid being sprayed all over the place.

I recall a construction site I was working on, where an excavator had one of it's batteries (lead acid) explode shortly after it was started. It was much more than just blowing the top off. Lead plates were moving at enough velocity to damage the electrical and cooling systems, along with the adjoining parallel battery. It sounded like a shotgun blast when it happened.

Wawa:
Last time I played with a common one that runs against the tyre I wasn't so lucky.
They must have improved a lot.
Leo..

Last time I had to use one (early 80's) was riding my bike at 4:30am to work on a farm picking corn. After 7 miles, it felt like I was dragging a cinderblock behind the bike

A 7Ah battery is probably a 'sealed' gel type rather than an 'open' wet acid type. As such the gasses generated by charging are recombined with no release under normal operation. Although such batteries are described as 'vented' the gas released is virtually zero, so not a realistic hazard.

What you have to do initially is evaluate what the daily Ah consumption is. For example if your system consumes 100mA then in 24hours your system will consume 2.4Ah. You now need to ensure your generator can replace this plus say another 40% to allow for system and chemical inefficiencies. So for 2.4Ah consumed, your generator will need to feed back around 3.4Ah. Hence the dynamo will be required to supply 3.4/24 = 140mA.

The actual Ah rating of the battery is mainly relevant to how long the system will continue to run if you do not replace the energy consumed.

There is lots of useful information about charging batteries of all types at www.batteryuniversity.com.

See this link for Lead Acid Battery.

I'd add a diode (1n400x?) in series so that the battery didn't discharge through the regulator when there's no ac supply..

Allan

tinman13kup:
I recall a construction site I was working on, where an excavator had one of it's batteries (lead acid) explode shortly after it was started. It was much more than just blowing the top off. Lead plates were moving at enough velocity to damage the electrical and cooling systems, along with the adjoining parallel battery. It sounded like a shotgun blast when it happened.

Years ago I went to a mini-mart to get a slushee. When I came out, I put the key in the ignition, turned it and heard an amazingly loud BANG. I thought someone's car backfired or something.

I turned the key again and nothing happened. I opened the door and noticed that the dome light was dim. I turned the key again and the dome light went out.

At this point I knew I had some kind of battery problem, but I still didn't think that the "bang" was from me.

I opened the hood and saw the battery with the top blown off, the sides bulged and acid dripping off everything.

What happened was one of the inter-cell bus bars came loose and the spark ignited the hydrogen.

I took a small set of vice-grips and clamped the open bus connection back together and amazingly the car started!

So I drove home with my hood 1/4 open, the vice grips sticking up out of the battery. At home I took the hose and sprayed off everything, trying to get rid of the acid. I must not have gotten it all because I had nothing but electrical problems after that (corroded wires, headlights and running lights that died, etc).

Never did get all the acid out. :frowning: Thank goodness I wasn't doing something like jump-starting the car and have the battery and acid explode in my face!