Not sure if this will be of interest but I've just dug out the parts of my old Land Rover lamp charger.

Plan is to fit it all into a box with a cigar lighter plug.

5.1 volt reg on overlarge heat sink.
Input 12 volt, output 5.1 volts At 3 amps.
🔗Personal-Album-1695-Image-32742[linkphoto]Personal-Album-1695-Image-32742[/linkphoto][/link]
Contact board
🔗Personal-Album-1695-Image-32743[linkphoto]Personal-Album-1695-Image-32743[/linkphoto][/link]

Hi Mr Morlock
Interesting bit of kit, but I am iffy about the 3 amps bit, assuming it’s correct.
The Oldham ammeters shown are reading 1 amp when needle is at the letter "C" in "Charge". Right over is 2 amps, and as I understand it an Oldham battery should not be charged at more than 1 amp. The older chargers will drop to about 350 mA when the lamp is fully charged and as this is a trickle no harm will be done.
More recent electronic chargers probably turn the charge right off, someone will know more about this than me.

---

Hi Mr Morlock
Interesting bit of kit, but I am iffy about the 3 amps bit, assuming it’s correct.
The Oldham ammeters shown are reading 1 amp when needle is at the letter "C" in "Charge". Right over is 2 amps, and as I understand it an Oldham battery should not be charged at more than 1 amp. The older chargers will drop to about 350 mA when the lamp is fully charged and as this is a trickle no harm will be done.
More recent electronic chargers probably turn the charge right off, someone will know more about this than me.

Hi Mr Fellows, the three amp output is a bit iffy for two flat lamps but the regulator does have overload protection.
At times of doubt I used to stagger the lamp connection times.

The kit was made up in the 80s when I beleive the correct charging voltage was 5.1, (non maintenance free batteries)?
I may have to fiddle the circuitry if I use it with maintenace free Oldham batteries.

I would like to meet you sometime, if I do there is a pint for you.
Anyway, if its any use to you at all I have made an Oldham charger from a Farnell 5 volt PSU and a 0.47 ohm 10 watt resistor (0R47) which gives perfect charging current for a single lamp. All in a neat little plastic box with a genuine Oldham ammeter and charging clip.
I dont know what resistors there are in your charger but at 12 volt input would have to be something a bit heavy.

More edit
Unless of course there is a voltage reducer of some sort.

---

I would like to meet you sometime, if I do there is a pint for you.
Anyway, if its any use to you at all I have made an Oldham charger from a Farnell 5 volt PSU and a 0.47 ohm 10 watt resistor (0R47) which gives perfect charging current for a single lamp. All in a neat little plastic box with a genuine Oldham ammeter and charging clip.
I dont know what resistors there are in your charger but at 12 volt input would have to be something a bit heavy.

More edit
Unless of course there is a voltage reducer of some sort.

No problem with a meet up as I will be around Brum/Wolverhampton for a lot of the summer. 🙂

There is an LM123 regulator so no resistors, just two capacitors.
http://www.national.com/mpf/LM/LM123.html 

What is the input voltage for the Farnell PSU?

I would like to meet you sometime, if I do there is a pint for you.
Anyway, if its any use to you at all I have made an Oldham charger from a Farnell 5 volt PSU and a 0.47 ohm 10 watt resistor (0R47) which gives perfect charging current for a single lamp. All in a neat little plastic box with a genuine Oldham ammeter and charging clip.
I dont know what resistors there are in your charger but at 12 volt input would have to be something a bit heavy.

More edit
Unless of course there is a voltage reducer of some sort.

No problem with a meet up as I will be around Brum/Wolverhampton for a lot of the summer. 🙂

There is an LM123 regulator so no resistors, just two capacitors.
http://www.national.com/mpf/LM/LM123.html 

What is the input voltage for the Farnell PSU?

Its just standard mains, 220 - 240V. Sorry, I was a bit misleading.

---

quote]

Its just standard mains, 220 - 240V. Sorry, I was a bit misleading.

The Farnell unit may be better than my present set up.
🔗Personal-Album-1695-Image-32747[linkphoto]Personal-Album-1695-Image-32747[/linkphoto][/link]

HI Roy & Morlock,
Interesting stuff. Just a few pointers though Roy, Lead acid batteries need a constant voltage to charge them so 5 to 5.1V is ideal and no dropper resistor needed. Depending on the state of discharge of the battery will command the current it will draw. ie totally flat a lot of current half flat, a medium ammount. I have to say that the charger I built using an old PC PSU has been working well for 18 months now without fault. All you do is tap into the 5V line which is good for about 20 amps even on the smaller models. This is what mine looks like and will easily handle 10 lamps fully discharged.
🔗Personal-Album-342-Image-152[linkphoto]Personal-Album-342-Image-152[/linkphoto][/link]
A flat battery on this set up will draw less than an amp and so gassing is kept to a minimum. I'll put up some pics of how to do the connections in a minute. 🙂

---

Oldham Charger from a PC PSU.

Most PSU’s have two sets of radial wires fitted with plugs viz 🔗Personal-Album-342-Image-151[linkphoto]Personal-Album-342-Image-151[/linkphoto][/link]

All these plugs carry 5V and each radial is good for about 10 amps, more on larger models. On my model I used one radial for the top row and the other for the bottom.

The wire colours are standard whatever size, model or manufacturer and are as follows RED = +ve and BLACK = -ve. Forget the others.


Now if your PSU does not have a remote push button switch then you must hotwire it to get the thing to switch on. This is easily achieved by linking out two connections on the motherboard plug see picture below. There is only ONE GREEN wire and this must be linked to any of the black wires on the same plug. If you run a couple of wires from this to a switch you can mount it on the front panel. I added a pilot lamp connected to the 5V line to let me know that the thing is on.
🔗Personal-Album-342-Image-150[linkphoto]Personal-Album-342-Image-150[/linkphoto][/link]
Now when you plug in your PSU it should spring to life.
I was going to add ammeters but this would have increased the size of the panel significantly. All I do when I need to measure the current on any lamp now is use a couple of wires fitted with banana plugs at one end and then solder the wires at the other end to each side of a piece of double sided circuit board. Then all you do is push the plugs into your multimeter and slip the circuit board between the lamp and the spring contact on the charger. This works a treat and the whole thing is light enough to be portable so when we go away as a gang this goes with us.

---

HI Roy & Morlock,
Interesting stuff. Just a few pointers though Roy, Lead acid batteries need a constant voltage to charge them so 5 to 5.1V is ideal and no dropper resistor needed. 🙂

Hi Roy
The resistor is recomended (& employed in their chargers) by Oldham (it is inherant in the charge meter) & IIRC is around 0.3 Ohm. Oldham refer to it as "modified constant potential charging".
The "Farnell" route is more popular than I thought - my effort, in use for over 20yrs!
[img]http://www.aditnow.co.uk/showimage/Personal-Album-1036-Image-33134/?h=105[/img]

---

Some excellent suggestions. 🙂

A bit late getting back to this post. On the subject of a series resistor cum Ammeter, on Oldham Chargers. Its inclusion is as a safeguard against the charger being short circuited across the lamp pins. Rather than the charger suddenly having a large load appear across it, the load is diverted into the resistor (which is now in parallel) and acts as a load for the charger albeit a large one. In the case of a .3 Ohm resistance shown by the ammeter, this would sink about 16.6 Amps. I've seen a light bulb used in one homebrew charger so if there was a short the bulb lit; much better than a fuse.
Anyway here are a few more pics of the one I built with the PC power supply. By the way, these pSU's are short circuit protected to the hilt so no real need for the series resistor.

🔗Personal-Album-342-Image-33290[linkphoto]Personal-Album-342-Image-33290[/linkphoto][/link]

🔗Personal-Album-342-Image-33289[linkphoto]Personal-Album-342-Image-33289[/linkphoto][/link]

---

That's an impressive bit of kit. :thumbsup:
There's a lot of skill and thought going into these cost effective chargers and lamps. 😉