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[Stan]

Need help with this one not sure where the incoming red cable connects to. Also this charger was designed for Nicads not sure if it can be used to charge NIMH batteries a very old piece of kit please note this is not mine.


Stan.

[JimG]

As it is purely a timed charger with no automatic charge cut off it will work with NiMh cells as well as NiCd. However as it relies on guessing how much charge is left in the cells before setting charge current and time it will probably overcharge them causing them to get rather hot and reducing their life. The best thing to do with one of these chargers is bin it and get a decent modern charger.
Jim

[Stan]

Hi Jim have agree should be in the bin but i still need know position of the red wire. Please note this is not my item.


Stan.

[HMS Invisible]

Need help with this one not sure where the incoming red cable connects to. Also this charger was designed for Nicads not sure if it can be used to charge NIMH batteries a very old piece of kit please note this is not mine.


Stan.

The whole box is a battery Y-splitter with resistors to regulate the current to a pair of lower voltage batteries. The rotary countdown timer is wired for two separate single switches. Each then gets fused and contains a series resistor selected via the rotary switch. The timer contacts open at the end of the countdown period to trickle charge each pack via a 22Ω resistor.

There are only two possibilities which may explain if you have a loose red wire: either a direct (1) common +ve or a (2) common -ve connection from the 12v battery to both race pack connectors (Tamiya) via a y-connecton.
  The opposite pole of the 12v battery also splits via  y-connecton inside the box. But it feeds through a pair of timed circuits to the opposite pins of Nicad1 & Nicad2.  If the owner removed the Tamiya connectors  (Nicad1 & Nicad2) then you are possibly left with one loose red wire and two other junctions or wires.

I think it is a keeper if there is the room for it. Just mind, without diodes, it will disharge the packs if you short the 12v crocodile clips. The workmanship leaves the possibility of shorting uninsulated connections.

[roycv]

I agree it should be disposed of.  I had a similar one with an MFA (clockwork) timer that did not always start, I was lucky I checked on it by chance and found it had failed to start, but current connected.  Could have been nasty.
Long gone in the bin!
Roy

[JimG]

Hi Jim have agree should be in the bin but i still need know position of the red wire. Please note this is not my item.


Stan.

Point out to the owner that continued use of this is a major fire risk and its time to replace not repair.
Jim

[Stan]

It looks like it is going to the model builders grave yard but in its time it served us all well. And of course you could repair it very easily not like today's throw away society.


Stan.   Club member will order new item and it will be all

[HMS Invisible]

The field charging task is covered by the familiar 4-button multi chargers, though they have one output.
If it is scrapped you get a pair of handy five amp ammeters, some high power resistors and a countdown timer.

[RST]

First time I saw that I also thought what a great source of repurposing for meters, switches etc. I hold no nostalgia for that like I don't have for CRT TV's with pushbuttons.  That shouldn't be scrapped though. And there are far safer chargers out there now for not much outlay.  Mind you I found one of those o eBay at the moment wanting pretty much 60USD!

[malcolmfrary]

First time I saw that I also thought what a great source of repurposing for meters, switches etc. I hold no nostalgia for that like I don't have for CRT TV's with pushbuttons.  That shouldn't be scrapped though. And there are far safer chargers out there now for not much outlay.  Mind you I found one of those o eBay at the moment wanting pretty much 60USD!

Yes, a parts mine.
Normal rules of the road that I would be thinking, is " Ground line universally black wire.  Positive in to wherever it starts to be switched, red, or something with a strong red component."  Looks like MFA, when they built it, didn't have quite the range of wire colours available that they maybe should.  Looking at the layout, not knowing exactly what is going on inside the switches, but looking at the other components, I have to wonder why they bothered with the voltage labelling.  It does look to a casual glance, is if the switch pointer doesn't really alter the circuit, but just acts as a reminder as to what battery should be connected.
Those big white things are either 10 or 7 Watt resistors mounted on a heat sink.  From experience, they can get really, really hot.  If the heat sink is replaced by a well wrapped wick, you have the basis of an oil evaprating smoke unit, but this is not for the squeamish.

[HMS Invisible]

Normal rules of the road that I would be thinking, is " Ground line universally black wire.  Positive in to wherever it starts to be switched, red, or something with a strong red component."

Yes, and it looks like the loose red +ve 12volt input would have connected to the ammeter terminals on right side, looking from the back. The +ve of each Nicad looks to connect via red striped pvc cable to top left & top right of timer (1 &2). That would mean -ve (or ground) from all three batteries just forms an isolated Y-connection

Looks like MFA, when they built it, didn't have quite the range of wire colours available that they maybe should.  Looking at the layout, not knowing exactly what is going on inside the switches, but looking at the other components, I have to wonder why they bothered with the voltage labelling.  It does look to a casual glance, is if the switch pointer doesn't really alter the circuit, but just acts as a reminder as to what battery should be connected.Those big white things are either 10 or 7 Watt resistors mounted on a heat sink.  From experience, they can get really, really hot.  If the heat sink is replaced by a well wrapped wick, you have the basis of an oil evaprating smoke unit, but this is not for the squeamish.

It is clearer when you see the switches ar 3 pole 4-position rotary Lorlin with just 2 of the poles used
@ 6volt setting two power resistors are in series
@ 7.2 one is shorted, leaving one
@ 8.4 two are in parallel
@ 9.6 the power resistors are bypassed

[grendel]

I remember building a similar timed circuit for a RC car, back in the days of mardave cars, you used a 25W 1Ohm resistor connected to a car battery, these resistors got nicely hot, - hot enough to brand your finger when you touched them, and charging the 7.2V pack in 20 minutes I believe my timer came out of a spin dryer.

[Stan]

Problem now sorted working fine.


Stan.

[RST]

One honest answer would be if you had that broken wire to take a good hard magnified look and look for some kind of teminal or otherwise and look for signs of a bit "broken off" somewhere.  But I don't think anyone was going to suggest that here to be honest

[chas]

Hi rst, I doubt anyone would suggest it because if the terminal was mid identified, an easy mistake to make, it could be dangerous. Let's face it, we all know modelers who've connected an ESC the wrong way round so repairing a mains device without enough understanding could be terminal.  ( pun intended)
Chas

[JimG]

No need to worry about mistakes with mains as these chargers were for a 12V input only, normally a car battery. Although an accidental short through misconnecting could lead to some very hot wires (possibly a fire).
Jim

[Andy M]

I had a fast charger for nicads that was just a big gold coloured alloy heatsink with resistor inside, no timer or anything, you were supposed to disconnect it once the battery pack was warm! Think they call them I E D s now.

[grendel]

yes the old 1 ohm resistor 50W direct across a car battery to a 7.2V nicad pack for 20 minutes- I used to have one with a spin dryer timer to charge my Mardave 1/10 scale electric car between races (anyone else remember the old original mardave cars with the aluminium battery trays down each side)

[Andy M]

I always thought there was something missing in that charging setup, now I know what it was....... Safety! 😁