Five NiCds implies what charging voltage?

[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