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Basic battery charger

Not a smart/intelligent charger

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Nathan Sharpe08/02/2020 23:02:59
149 forum posts

Do any of you know where I can buy an old fashioned non smart charger for auto 12v batteries? I have a number of L/A 12v batteries that I could possibly use for driving my emergency heating pump invertor but only have an "intelligent" charger. These batteries are showing JUST less than "V per cell. I had thought of starting the car and using jump leads to try and charge them but it seems more costly in fuel for six 12v batteries.

Any help and you have my thanks. Nathan.

Nathan Sharpe08/02/2020 23:04:26
149 forum posts

Should have read" just less than 2v per cell. Nathan

Steviegtr08/02/2020 23:14:23
1234 forum posts
115 photos

There are plenty for sale on ebay. I have brought many dud batteries back to life using the basic older chargers. If you really wanted you could make one with a 240-14v transformer & a full wave rectifier / diode.


Bob Brown 108/02/2020 23:16:33
1010 forum posts
127 photos

Just place a good battery in parallel for around 1 hour.

not done it yet09/02/2020 08:24:07
4658 forum posts
16 photos

There are ‘intelligent’ battery chargers and “really intelligent” battery chargers. They are not all the same. The best ones are far better than the old simple type of charger.

Jim Young 209/02/2020 10:01:14
21 forum posts
5 photos

Nathan....tell us more about the project!

RMA09/02/2020 10:50:38
241 forum posts
4 photos

I have intelligent chargers and have revived 'dud' batteries with them. You have to be patient and leave them connected for quite a long time. Worth a try before you spend any more and collect another item.

SillyOldDuffer09/02/2020 11:00:36
5790 forum posts
1232 photos
Posted by Steviegtr on 08/02/2020 23:14:23:

... I have brought many dud batteries back to life using the basic older chargers...


Batteries brought 'back-to-life' by this method are far from being in 'as new' condition. It's a reasonable way of extending the life of a non-critical battery, but you don't want one in your car unless poverty forces it. Unreliable. It's the sort of trick that gave second-hand car dealers a bad name.

My experience with car batteries for other than in-vehicle use has been poor. They're designed to deliver a short burst of very high current during starting, and then to take a relatively fast recharge. They dislike long low-current discharge and trickle recharging intensely and don't last long, and a rejuvenated battery is already in poor order.

Better to use the right type of battery for emergency use, unless of course, it's acceptable to risk the battery not working when needed.


Steviegtr09/02/2020 12:19:05
1234 forum posts
115 photos

I would never put a duff battery on any automotive. I had a few battery powered items in my garage. One being my bike lift made from a transit tipper pump & a ram from an old tractor.


Simon Barr09/02/2020 12:30:04
15 forum posts
12 photos

As far as intelligent chargers go I can recommend Ctek ones. I've had one for around seven years now and it is fantastic, not cheap but fantastic. It's been used on all sizes of batteries and even has an AGM setting. In my experience 'old fashioned' chargers are just as likely to knacker a battery as charge it, they all overcharge to some degree. You can just leave an intelligent one to analyse and charge appropriately.

Well worth what it cost me.

Howard Lewis09/02/2020 12:32:46
3281 forum posts
2 photos

The most basic battery charger for a 12V battery would be a transformer delivering about 14 - 15 volts with a rectifier between the secondary winding and the load. Ideally the rectifier should be a bridge type, to give a smoother output.

(You need more than 1.3 V because the diode will drop about 1.4 V )

being absolutely basic, it will be unregulated, and the output voltage will be lower ,when first connected because of the current draw. As the cell voltage increases, the current draw will decrease and the measured voltage increase.

A long time before rocket science.


Steviegtr09/02/2020 14:19:23
1234 forum posts
115 photos

These 3 are all smart chargers. The one in the box I bought before winter for the car. Still not got it fitted. The optimate about 3 months ago showed flat battery & then the desulphate light came on. Left it alone & the next day all was well again. Bike in it's 3rd year & battery still good.

Steve.charger.jpgcharger 2.jpgcharger 3.jpg

Nathan Sharpe09/02/2020 21:21:54
149 forum posts

Thanks for all the responses.

Jim Young 2.

Not a project, I usually have a few ex car batteries around for winter use on the power inverter for the few times we have power outages. I just left these too long before charging. This gives me the ability to run the central heating pump , all other controls are manual.


They answer my needs and have done for many years.


Neither would I but they can be useful for jumping a cold battery.


RMA09/02/2020 21:50:13
241 forum posts
4 photos
Posted by Simon Barr on 09/02/2020 12:30:04:

As far as intelligent chargers go I can recommend Ctek ones. I've had one for around seven years now and it is fantastic, not cheap but fantastic. It's been used on all sizes of batteries and even has an AGM setting. In my experience 'old fashioned' chargers are just as likely to knacker a battery as charge it, they all overcharge to some degree. You can just leave an intelligent one to analyse and charge appropriately.

Well worth what it cost me.

Some members of the Jag club have Ctek and swear by them. I have a couple of intelligent chargers from Lidl at £13.99 each and they are great. I'm no electrical expert, but apparently they pulse a dead battery back to life; charge it and then discharge and trickle charge alternately if left connected. I keep one on my Jaguar all the time when laid up for any length of time, as these cars will soon drain a battery when idle for a time.

Steviegtr09/02/2020 23:22:45
1234 forum posts
115 photos

I have not found a problem with my F-type. I bought a charger for over the winter & never fitted it, but went to start the car the other day for a run out & the battery was still good after months of being stood. Did make me worry though with the red blinking light of the alarm system running all that time. Note to one's self connect up the charger unit.


RMA10/02/2020 08:34:54
241 forum posts
4 photos

Mine is a lot older than yours and they are notorious for electrical problems such as windows losing memory or the top sluggish in operation, even when the battery is a little below par, so it's a good idea to keep an intelligent charger to hand. I even have a spare battery which I keep charged just in case, although they are very large and heavy and awkward to swap over in the boot! If the car is a daily runner, there shouldn't be a problem, but I do less than 2k miles per annum in it so the charger in invaluable.

The completely dead battery was on my digger and this did get left for long periods. These chargers worked wonders on that battery!

Peter G. Shaw10/02/2020 11:25:23
1100 forum posts
44 photos

I have never used, or felt the need for, smart charger, relying instead on a bog-standard home built device constructed something like 50+ years ago. It consists of a 240v transformer with two outputs, one for 6v & the other for 12V feeding into a selenium full wave bridge rectifier via a rather large rheostat and a moving iron ammeter.

I also built the batterty monitoring device published in ME some 20 years ago, could it be by Gordon Read? This maintains the battery voltage between two set limits, and cycles the battery as well, this under control of a relay. Unfortunately, during the winter of 1995 (I think), the temperature around here dropped rather dramatically (the hydraulic fluid in the lifeboat stationed 7 miles away turned to slush and ruined the engines!), and the relay froze in the discharge position. The battery was sat on a concrete floor, adjacent to a door, and as far as I can tell, one end cell must have frozen. That was the only battery that I have ever ruined in 50+ years of using them.

I have had problems with so-called leisure batteries for my caravan. There used to be, and maybe for all I know still are, cheap batteries available for around £30 supposedly suitable for caravans and described as 75Amp batteries. Unfortunately, their capacity was somwhere in the region of 30hours at the usuall 20 hour rate. On buying an Exide leisure battery, firstly I very nearly dropped it due to it's weight, secondly at was rated at 75Ah, note the extra letter, at the 20 hour rate, and easily exceeded that rating on test. Today, if I need a new leisure battery, I look for a recognised make, Exide being my favourite, and secondly, ensure that the rating is for at least 75Ah at the 20 hour rate. I then don't have any problems other than self-inflicted ones. If anyone describes them as a 75Amp battery, I always go elsewhere.

It should be noted that leisure batteries are designed for deep discharge, whereas, as has been said, starter batteries as fitted to vehicles, are designed for very heavy, short term discharges, followed by moderately high re-charging. Here again, I have been caught with cheapish batteries with a, say, 3 year warranty, and lasting on the car, a month or two over the 3 years, whereas, a Bosch 4 year warranty was still working, albeit on its last legs at 6 years old. My present car, a Toyota Avensis 1,8 petrol, had to have it's battery replaced at just over the 3 years: it now has a Bosch 5 year warranty battery which is almost 3 1/2 years old.

Finally, may I comment on telephone exchange batteries, the ones that were used with old-fashioned Strowger exchanges. In many instances these were many years old, possibly into the 20's. Very early on these were used in pairs on a 24 hour charge-discharge system, later they were used either singly or in parallel on a partial charge/discharge where as the battery became discharged, the rectifier would automatically switch on and supply some of the daytime load except through the night when the load dropped and all the charging current went into the battery, and later still, on a parallel float system where the main load was taken by automatically controlled mains driven rectifier units.

Peter G. Shaw

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