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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 10th Jan 2021, 6:48 pm   #21
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Default Re: Car battery charger project.

A big zener diode was used on British motorcycles for charge regulation. It was crude but effective (just like the 'bikes) for wet cell batteries. I wouldn't bother making your own as things like these https://www.screwfix.com/c/auto-clea...rs/cat12010001 are readily available and not costly.
 
Old 10th Jan 2021, 8:52 pm   #22
Ed_Dinning
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Default Re: Car battery charger project.

Hi Malc, I may have a simple cheap and cheerful ammeter (0-4A?) if you are interested

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Old 10th Jan 2021, 9:58 pm   #23
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Default Re: Car battery charger project.

I have had quite a few very old chargers over the years. Throw out the selenium rectifier and fit a modern silicon bridge. That will increase the output voltage, not a good idea, so you need to add a bit of series resistance. I usually use maybe three wire wounds, 0.5, 1.0 and 2.2 ohm, switched to control charge current.
I have recently bought a modern intelligent one, which I regularly cycle over all my lead acids used for whatever is needed including "jumping" the bike or even car.
My good old 'un does have 6v, unlike the clever one, so that is useful for the 6v coil ignition I fitted to the cement mixer.
Any old electrolytic connected to the output will confirm the maximum output voltage.
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Old 10th Jan 2021, 10:20 pm   #24
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Default Re: Car battery charger project.

Ed, thanks for the offer of the meter PM sent. Just need a 0-15 volt meter now.
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Old 10th Jan 2021, 11:58 pm   #25
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Default Re: Car battery charger project.

There isn't much in older chargers, as far as my experience of seeing inside a couple to repair broken leads goes. What is the extra circuitry inside one of those 'smart' chargers one can leave connected and that 'sense' battery state? Is that easily added in to something made by the home mechanic, taking into account the behaviour in Diabolical Artificer's PDF?
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Old 11th Jan 2021, 12:11 am   #26
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Default Re: Car battery charger project.

A reminder start mentioning vehicles engines etc will just get the thread closed, posts edited or deleted Oldcodger did warn of this early in the thread.

Cheers

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Old 11th Jan 2021, 11:44 am   #27
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Default Re: Car battery charger project.

Quote:
Originally Posted by Uncle Bulgaria View Post
There isn't much in older chargers, as far as my experience of seeing inside a couple to repair broken leads goes. What is the extra circuitry inside one of those 'smart' chargers one can leave connected and that 'sense' battery state? Is that easily added in to something made by the home mechanic, taking into account the behaviour in Diabolical Artificer's PDF?
The extra circuitry controls the output voltage and monitors the current. This allows it to charge in several steps. For example it can charge at around 14.4v to get the battery towards full more quickly. Then as the current reduces, it can reduce the voltage to something around 13v, to avoid the battery from being overcharged. Some chargers have multiple steps, one of mine has something like 7 or 8. I'd say it's not something easy to add. Discount supermarkets often have their own branded smart chargers for relatively little money so it's not really worth it anyway.
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Old 11th Jan 2021, 2:18 pm   #28
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Default Re: Car battery charger project.

I replaced a selenium rectifier with a silicon one in a 12v battery charger in the distant past and this resulted in an excessive charge current due to the increased voltage. I spotted the transformer overheating and switched off quick.

I cured this by adding a few turns to the secondary winding and connecting them in anti-phase, I had to experiment with the number of turns to get the charge current right, only needed about 5 turns IIRC. I could only do that as I had enough space to get some turns on the transformer.

The advantage with this method vis adding resistance is the voltage is dropped so the battery won’t overcharge.
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Old 11th Jan 2021, 2:44 pm   #29
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Default Re: Car battery charger project.

Hmm. Plenty of 8-16v dashmount voltmeters around, but where does Malc get a 0-15v..? (unless repurposing a more sensitive one with a series resistance)

I recall that my ancient charger shows an off-load output of around 16v on an Avo (no smoothing and a selenium rectifier)- is this a potential concern with a vehicle 45Ah battery?...and is my old meter likely to be showing the peak voltage?

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Old 11th Jan 2021, 5:10 pm   #30
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Default Re: Car battery charger project.

(My mistake, there's loads of 0-15v voltmeters available, but many are square modern lab bench type)
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Old 11th Jan 2021, 10:11 pm   #31
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Default Re: Car battery charger project.

Hi Malc, is this ammeter suitable?
A bit garish but goes up to 10A. There might be a lower current one (4A?) about but not turned it up yet, nor any similar voltmeters. Approx 2" square
I do have a few 1R or so 20W resistors if you need them for current limiting, possibly even a switch to go with them.

PM me with address details etc

Cheers, Ed
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Old 11th Jan 2021, 10:19 pm   #32
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Default Re: Car battery charger project.

Hi Ed, thanks for the offer but i think i will use a 0-4 or 5a I sent you a PM yesterday, Malc.
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Old 12th Jan 2021, 10:22 pm   #33
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Default Re: Car battery charger project.

Hi Malc, pictures of the 4A & 5A meters (a bit under 2" dia) as well as a square 24v voltmeter. Any use?

Ed
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Old 13th Jan 2021, 10:56 am   #34
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Default Re: Car battery charger project.

Hi Ed, PM sent. Cheers, Malc.
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