Why did the charger stop?

[Oops]

I bought a Multiplex radio via an auction and work and illness meant it was forgotten for 3-4 years. Recently I went to turn it on and it wouldn't then I plugged in the Multiplex USB to din charge plug which would not light up or charge.

So I took the permabatt 6 nimh cell pack out of the tx and connected it to my small oldish lipo/nimh overlander battery charger. I guessed at a charge rate of .2 amp and started charging using the manual charge setting of the charger. An auto setting is available but I don't understand from the manual what the difference is.

The multiplex manual is fulsome and told me the 7.2v pack is 2100ma and normal charge rate is 210ma and will take 16 hours. It also says that will give 8 hours of flying. It says the radio does not have to be charged when in storage but also says not to allow deep discharge under 5.6v which of course I did. It gives a delta peak value which the overlander doesn't allow me to set but I've another charger that does.

After approx 5 hours of charging I was about to go to bed so went to turn the charget off. As I stood in front of it it signalled that the charge was complete! I saw 800 approx on the charger which I think is the number of ma charged?

This morning I put the pack back in the radio, a Royal Pro 7 and turned it on. It says 8.2v and flying time 56mins.

Why did the charger stop?

[FlyinBrian]

You need a new battery,

No batteries like being totally discharged! NiMh suffer from self discharge so over time they will go flat (Enerloop are much better than normal NiMh but are more costly)

It has probably suffered from some chemical change internally or crystals can form.

Your MPX charger did not like being connected to a totally flat battery but your Overlander tried to charge but probably saw a "false peak" which caused it to stop, thinking the battery was full.

Even in normal use a NiMh battery would do well to last four years.

[Trevor Crook]

If your charger can perform a discharge/charge cycle, it may be worth trying this. I've restored several NiMh packs that have been neglected by using the charger to discharge at 1A to 1V/cell, then perform a delta peak charge at 0.8A. I've found that charge current avoids false peaking, and that a couple of cycles restores most of the capacity.

If you do this though, leave the battery for a few days then test its capacity, either on a charger or in the tranny, in case it was a temporary recovery. If in any doubt, obviously replace the pack. Modern Eneloop types are very good.

[Oops]

You may be right in saying I need a new battery. I'm reminded of a car where I left the door ajar and when I went to test the battery it read nothing. Ie not sub 11v or sub 5v but nothing. Neither my ctek smart charger nor my dc to dc optimate would attempt to charge it so I dug out an old 250ma primitive trickle charger until the v was approved of by the ctek and the battery's been used in the car ever since.

I agree with you; I think both the pb and nimh batteries have been damaged but maybe the latter might be usable still. Thanks for the explanation of false peak. On the mpx radio it says the battery capacity is 1500ma and charge is 1490 and the mpx charger still won't charge. I'm going to try with a different nimh charger at .05c and see what happens. Then I guess I'll try a discharge and see if I can any headroom for the mpxcharger to start working and if all that fails replace the battery pack, it' hidroysly expensive though for only 2100ma for 6 cells.

[Oops]

Thanks Trevor I'd not seen your post when I was writing mine nice to think there may be hope! I get an implication that maybe I'm charging at too low a rate. I'd thought it safer to do that but as you and Brian will have gathered I'm doing this emprically not on any science . Ok, I will try those suggestions and yes I will def leave for some days / keep a close eye, I did similar with my sulfated pb battery.

Marc

[Richard Clark 2]

Posted by Oops on 07/06/2020 08:28:52:

Thanks Trevor I'd not seen your post when I was writing mine nice to think there may be hope! I get an implication that maybe I'm charging at too low a rate. I'd thought it safer to do that but as you and Brian will have gathered I'm doing this emprically not on any science . Ok, I will try those suggestions and yes I will def leave for some days / keep a close eye, I did similar with my sulfated pb battery.

Marc

You often get false peaks or refusal to charge at all when charging Nimh cells from flat. It usually happens because you have either set a low charge rate or CORRECTLY set the charger to 'Sensitive' or 'Nimh'.

Try it with the charger set to about 1 amp (1000 mA) and the peak set to 'Normal' or 'Nicad' and it should work. BUT ONLY LEAVE IT LIKE THIS FOR ABOUT TEN MINUTES.

Then stop the charger and set it to the correct position for Nimh and start again.

Ideally do both processes with the battery connected to the charger directly, not via the Multiplex transmitter's DIN socket as that way you don't involve the transmitter's protection circuit.

TAKE CARE. Via the DIN socket the older Evos, marked 'Evo' and maybe the older Cockpits could be damaged if you use a charger capable of charging more than about 8 cells and the manual that comes with them warns you about this.

The later ones, marked 'Royal' are ok with such chargers.. It's because some such chargers can produce a very high 'open circuit' voltage when switched on before connecting it to anything.

If you ever need it fixed or checked over  Mike Ridley of 'Model Radio Workshop', near Southampton is  the official service agent.

Edited By Richard Clark 2 on 07/06/2020 09:05:45

Edited By Richard Clark 2 on 07/06/2020 09:10:36

[MattyB]

Replace your pack - if it fails prematurely with no warning (which batteries like this will do if left completely flat for long periods) you will lose the model. There are places where it’s fine to economise, but power supply is not one of them; just not worth the risk.

Edited By MattyB on 07/06/2020 09:44:05

[Kevin Wilson]

"Why did the charger stop?"

Too low charge current giving a false peak.

I used to race RC cars and had a routine of cycling nimh & nicd cells.

I would see an improvement in capacity over 5 or 6 cycles. Never had the patience to do more.

3300mAh cells, charge at 5A discharge 1A but only because that's all my charger would do. Some race buddies had better dischargers up to 20A.

For AA I would go for 1 amp charge, 2 amp discharge.

Give your cells a good thumping Oops. They will love you for it.

[Shaun Walsh]

Is this the battery?

**LINK**

25 Euro plus shipping seems a small price compared to a lost model.

[Frank Skilbeck]

Is your Royal Pro still on 35 mhz or on 2.4ghz, the 8 hours refers to 35 mhz, you'll get way longer on 2.4 ghz, I think my Royal Pro 9 M-link fully charged shows over 17 hrs.

Also in the transmitter settings you can tell the Tx that the battery is fully charged, it will then measure the mah used and calculate the remaining life, it does tend to overestimate the self discharge rate of Nimh batteries though and will give a low remaining time if the tx hasn't been used for a while. If you charge the battery outside the transmitter it doesn't measure the mah you put back in, so you would need to manually reset the capacity.

BTW I had to replace the battery pack in my 12+ year old 35 mhz Cockpit Sx last year and just got a 6 cell AA pack of the correct configuration.

[Oops]

I'm such a t**. I last looked at this radio some 4 years ago and didn't know anything about it then. I've just realised that the cable I found marked multiplex and that 've been putting into the din socket on the back of the tx is a PC interface cable. No wonder it wouldn't charge.

The radio has been converted to 2.4 Frank. I see what you mean about setting the mah. I've found a cable that is not marked multiplex that has bananas one end and a din the other and once I've verified that it's a correct charge cable for the mpx I'll use that in future rather than direct to battery.

I've nimh pack I use eg for flying slope soarers but they are squarish 4-5 AA packs, did you actually find a 6 cell in the same shape as the permabatt? I don't see any signs of the pack being fubared but I'll put it through a few cycles.

[Frank Skilbeck]

The cable sounds like it will be fine.

This battery might fit, I think I got mine from Overlander I bought it at a show.

[Richard Clark 2]

Posted by Oops on 07/06/2020 18:17:42:

I'm such a t**. I last looked at this radio some 4 years ago and didn't know anything about it then. I've just realised that the cable I found marked multiplex and that 've been putting into the din socket on the back of the tx is a PC interface cable. No wonder it wouldn't charge.

The radio has been converted to 2.4 Frank. I see what you mean about setting the mah. I've found a cable that is not marked multiplex that has bananas one end and a din the other and once I've verified that it's a correct charge cable for the mpx I'll use that in future rather than direct to battery.

I've nimh pack I use eg for flying slope soarers but they are squarish 4-5 AA packs, did you actually find a 6 cell in the same shape as the permabatt? I don't see any signs of the pack being fubared but I'll put it through a few cycles.

I did wonder when you said "Multiplex to USB cable" in your initial post. The Multiplex charger cable has a 3 pin DIN on one end and a pair of 'banana' plugs on the other. This will fit the 7 pin DIN socket on the transmitter.

You cant use 'any old' DIN cable as there is no internationally accepted standard for the DIN pinout.

SO - the pinout you need -

Looking at the PIN end of a 3 or 5 pin 180 degree DIN connector with the notch at the bottom, you need the extreme left hand pin connected to the charger negative and the extreme right hand pin connected to the charger positive The other pins are not used.

The genuine Mulitplex battery should be the Permabatt+ (plus) . This has 6 Eneloops, the older one without the 'plus' has the older 'regular' cells. The one shown by Frank also has Eneloops but you would need to cut off the 'servo' type connector and solder on the cable from your old battery.