Electronics geeks, I need your help.

paul ron · Sep 27, 2012

I have an old Sunpak 611 in great working condition. It fires up using regular C batteries n off the wall adaptor but I want to rebuild the CL-1 cube with new NiMh sub C cells.

I don't have the old batteries in the cube so I have no idea how the thermistor(s) was hooked up. Anyone have any ideas or perhaps have an old CL-1 cube I can compare it to for wiring?

I put a set of NiCads in the cube without the thermistors n it charges just fine but I am worried when I get the new NiMh I am running the risk of overheatting em.

Any info is appreciated.

Mike Wilde · Sep 27, 2012

Well, the thermistor would have been set to feed a temperature variable resisitance to a regulator circuit. The regulator circuit would have been calibrated to limit the charge current to not overheat based on the nicad charge characteristic, which is likely not the same charge characteristic as NiMH. NI-MH generally can be charged faster thatn Ni-Cad, as I recall. Look up the technical charactersitics of the cells.

I am old school. My packs are generally on the end of a coiled cable, and i make them up from gelled lead acid batteries. I charge them fully winthin two days after using them, and sometimes months will go by before I ned to use it again. It will be still fully charged, and ready to go.

My work digicam is fed Ni-MH AA cells. If you don't charge them before you need them you are screwed, because high energy density or not, they are flat within 3 days of charging them.

paul ron · Sep 27, 2012

Thanks Mike. I do understand how they work, I just have no idea how or where to wire em in.

The cube is arranged as 2 cells on either side of teh cube wired in series. The flash n charger are internally jumpered so they are actually working as 6V in series. The charger does have 4 springs one for each cell so there must be a regulator sensor in there.

The values of the thermistors have been calculated so my cut off will be 5K. So far all that theory is just fine, just the physical placement of em is my only problem right now.

I did make a 6V external battery many years ago using this CL-1 holder... thus the reason it is empty now. I don't need as much juice as I did back in the day so I want to scale back n use the original CL-1 cube again. THe replacement cells are very cheap and will be more than I will ever need on any shoot. I tried my NiCads n I cna do at least a dozen rolls of film no problem n still have enough go go juice to keep going for a few more hours.

So if anyone still has the old masher battery pack, can you open her up n let me know where those thermistors go?

.

ic-racer · Sep 27, 2012

The thermistors in the Rollie packs are placed between the cells with some cotton packing and white thermal grease. Is that what you are asking? Or do you need to know to which contacts the thermistor is attached?

paul ron · Sep 27, 2012

I need to know where they solder to the batteries.

polyglot · Sep 28, 2012

The thermistor does not solder to the batteries, at least, not at both ends. If I had to guess, I would say that one side attaches to the most-negative end of the pack (assuming it's a PTC not NTC) but the other side of it needs its own contact so that some electronics can sense its resistance.

paul ron · Sep 28, 2012

polyglot said:
The thermistor does not solder to the batteries, at least, not at both ends. If I had to guess, I would say that one side attaches to the most-negative end of the pack (assuming it's a PTC not NTC) but the other side of it needs its own contact so that some electronics can sense its resistance.

I figured that out, but where exactly does it go? My batteries are arranged as 2 series cells on either side of a cube wth no cross connection between the pairs.

The flash has 4 contacts, 2 make an internal Minus to PLus cross connection... so the battery pack is acting as 4cells in series to make 6VDC.

The charger also has the same 4 contacts, with 2 internal formning a cross connection, but is charging with only 2 so the batteries are charging as 4 cells in series.

Now here is the hitch... the battery pack is keyed, it can be inserted in 2 directions, rotated 180°, so the terminals will still be the same polarity in pairs on both sides. ^=direction

^
+ _
l l
l l
_ +

internal cross jumper is at the back of both the flash n charger.

So where do you put the thermistor since both ends can be the front or back, none are end cells?

So if you have one of these packs, can you crack it open n tell me where it makes the connection? I'm not looking for therory, I need to know exactly where it physically solders to.

.

polyglot · Sep 28, 2012

I don't have one, sorry.

paul ron · Sep 28, 2012

I opened the charger today. It's a stupid charger with a bridge rectifier arrangement, some resistors, diodes and an LED. The LED comes on when the pack is inserted n goes out when batteries are removed. My guess is a thermistor is not the part to use, it should be a thermal switch of some sort to disengage the batteries when it gets too hot.

I'd really like to know what the origianls came with, stupid me threw it out years ago to make an external battery pack using plugs in the cube n extension wires to a sealed acid batttery.

.

polyglot · Sep 29, 2012

If that's what the charger is, I wouldn't use it - it will degrade your cells. Use eneloops or whatever in a proper smart-charger and insert them into the pack for use.

paul ron · Sep 29, 2012

Well I have the NiMh high power cells coming this week, too late for the eneloops. BTW Do they come in Sub C?

The charger is the Sunpak original n I was told by others that have upgraded to NiMh it works just fine.

Anyway, I'll just keep an eye on the temp as I time it to see how long it takes to get em up to 100°F, I was told that is the cut off threshold for these cells.

A smart charger is another posability n adapt it to my cell pack configuration?... That's a great idea!

Thanks for the ideas.

polyglot · Sep 29, 2012

If you don't use a smart charger, you *will* destroy the cells from overcharging. Temperature protection is one factor only; you need to cease charging at the correct time, which is when the cell voltage reaches its peak and then drops by 5mV. If charging doesn't cease then, the cells will be reduced in capacity and the pack will have a short life. If you charge at a low rate (12-hour), the cells should barely warm at all and that will give them the longest life. If you charge rapidly (1-hour rate), the cells will heat a lot, their life will be shortened and they will receive only a fraction of their full charge before hitting 37C.

You can build a higher-voltage smart charger to charge the whole pack but for balancing reasons, it's much much better to do it cell-by-cell. Since you're already into hacking up battery packs, I suggest you put a little 8-pin plug in there that allows you to wire the four cells individually into a 4-cell smart charger with a cable. The pack will last a lot longer and hold a lot more energy.

If I were building a battery pack now, I'd use 18650 lithiums.

paul ron · Sep 30, 2012

Last night I was looking at a smart charger I have laying around. I opened her up n was surprised how much electronics there are in this thing.. very impressive system.

It's a 4 cell meant for C size NiMh batteries that does em as 2/pair, not 4 in series. I also noticed it doesn't have any temp sensors in the compartment, it must have a different feedback system based on load n voltage. Well my batteries are arranged as 2/pair so I'm going to hot wire the outputs to the original charger's holder where my cube fits (disconnect the internal jumper) and do em like that.

.

Chan Tran · Sep 30, 2012

Hi Paul! Like Polygot said I read the document at the Energizer website they do recommend to charge cell by cell individually rather than charge them in series. The charger does several things to monitor the amount of charge. It checks to see if the voltage started to fall then it's full and also if the temperature raise rapidly then it's full. They do say that if you do not have the ability to monitor the charge like these smart charger then charge them at 10 hr rate so that there is less chance of over charging them. I wonder the sub C cells that you're getting what's the mA rating on them? I have found a lot of C and sub C NiMH cells that the capacity is about the same as AA cells although they are much bigger.

polyglot · Sep 30, 2012

If you have a 2x2 smart charger you can directly wire up to the pack, that'd be the perfect option - no need to have jumpers/switches to separate the pairs for charging.

All that electronics is usually a microcontroller running a PWM buck converter (current control) and ADC (voltage monitoring) for each set of cells. Actually there are some neat integrated charger-in-a-chip solutions you can buy now that do everything but a lot of the good chargers still do it all explicitly: bit of a combination of manufacturers selling stuff on fancy features like mAh logging and not-invented-here syndrome.

paul ron · Sep 30, 2012

The cells I ordered are 3300mAh NiMh...
http://www.voltmanbatteries.com/servlet/the-1449/SUB-dsh-C-3300MAH-NIMH-BATTERY/Detail

They are tack welding the tabs for me as well in pairs so all I have to do is drop em in. I wire4d up the smartcharger I have to my cube n that will work out just fine. This charger has a very populated circuit board, no doubt computerized.. looks way too advanced except the standard transformer and rectifiers, standard entrance power source although with regulators before the PCB. I'm impressed. I had this thing in my closet for years, never used it.. actually never knew I had it till now.

Problem solved! Always good to work these things out with others.

Thanks.

Electronics geeks, I need your help.

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