Five NiCds implies what charging voltage?

[broggerp]

Off the wall, but I know where to go with such questions. ;-)

I've an ancient (10+ yrs old) vinyl inflatable mattress with a (theoretically, once upon a time) rechargeable blower to fill/empty it.
I seem to have lost its wall-wart charger.
Inside I see no circuitry, an on-off switch, and a female charger port wired across a stack of five C-size NiCds.
There is no explanatory diagram label or embossed to indicate the charging voltage and polarity.

First guess: Would that be a 12-volt, DC charger?

Of course, the other question: the thing has *never* been charged or used. Are the batteries likely to work?

Thanks for any input,

Paul B.

[Duane Hess]

NiCADs are typically referenced as 1.2V, hence 6V for 5 in series. Other references are 1.25V. However, f1.2V seems way more common.

Can't help you with how much over 6V should be used for charging.

If possibe, charge them outside the device. I have 40yr old NiCADs that seem to work fine (very few). Most won't hold a chare, discharge quickly, etc. If NiCADs get warm while charging STOP. Unlike other batteries, they typically cool slightly when charging.

A word of warning, it might be well worth installing new NiCADs. I do not charge old BATTs long enough to be "full" even if apparently working 100%. Have forgotten to quit early and they do explode. Won't level the house but will break the frame of what they are in, which is typically plastic. (but even a single AA will sound like a loud pistol)

From the description, it sounds like there is no internal circuity. Might consider fabricating a removable battery pack utilizing a more modern battery technology. Lithium or NiMH; just have a config close to 6V. If the only device being powered is a pump motor, undoubtedly a variance of +/- 1V would EASILY be tollerated.

Batteries which have a button on top indicate the + end. Batteries that are smooth on both ends will have a "crimp ring" just below one end. I believe that is also the + end, but don't really know. Sometimes closely examining the charger port plug/recepticle will show +/-.

[Garth Wilson]

I don't know what the voltage will be; but NiCd charging should limit the current. Giving a constant voltage will probably get you in trouble. See https://en.wikipedia.org/wiki/Nickel%E2%...y#Charging

[Dieter]

(08-26-2017 02:20 AM)broggerp Wrote:  I've an ancient (10+ yrs old) vinyl inflatable mattress with a (theoretically, once upon a time) rechargeable blower to fill/empty it.
I seem to have lost its wall-wart charger.

You seem to have lots of AC-adapters. That's not chargers. They may only look the same.
AC-adapters just supply a voltage. Chargers control the current. That's a completely different thing. Never ever connect an AC-adapter directly to your battery pack!

(08-26-2017 02:20 AM)broggerp Wrote:  Inside I see no circuitry,

Sure. The current is set by the charger.

(08-26-2017 02:20 AM)broggerp Wrote:  First guess: Would that be a 12-volt, DC charger?

The output voltage of the charger (!) is not that important. It just has to be higher than the voltage of the five cells. During the charging process each cell can reach a voltage of ~1,4 V, so that's 7 V for five cells in series. So a charger (!) with 12 V output should be fine.

But that's not the most relevant point. The charger has to supply a certain current (!) to the cells. In the most simple case that's done with a resistor. For instance, 12 V charger output and an average battery voltge of 5 · 1,3 = 6,5 V, using a 20 Ohm resistor would yield a current of (12 – 6,5)/20 = 0,275 A or 275 mA. If your cells have a capacity of, say, 2000 mAh this would mean a charging time of 1,2 · 2000 / 110 = 8,7 hours. The 1,2 is a common efficiency factor for NiCd and NiMH batteries.

But once again: do not connect the batteries directly to the output of an AC-adapter! This would mean that the charging current is not limited at all.

(08-26-2017 02:20 AM)broggerp Wrote:  Of course, the other question: the thing has *never* been charged or used. Are the batteries likely to work?

They may work... if you charge them properly with a suffifiently low charging current. After a few cycles (charge-discharge-charge-discharge...) they may (!) recover. But just as well they may be dead.

Dieter

[Dave Frederickson]

I use a Tenergy smart pack charger.

http://www.tenergy.com/01006?sc=59&category=38155

It will automatically select the correct charging voltage for 2 - 6 cell battery packs. I've used it to charge Classic, Topcat, and 2225 battery packs.

Dave

[broggerp]

Thanks all!

(One simple alternative: use the double-action manual pump that normally packs with my inflatable dinghy.)

I appreciate the responses.