TOT Ni-Cads and NiMh

[The Natural Philosopher]

Only if you are gassing ethnic minorities with it.

Moles are exempt.

[Ian Field]

Perhaps you should try getting a clue, and a decent charger.

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Pulse chargers make *ALL* the difference.

[Bob]

They're not mine to chuck, they belong to the old dear next door who absolutely loves them! Mind you of the 36 I've looked at nearly half are beyond repair due to the batteries and/or water seepage, animal damage etc. Quite a few of the nicads worked after being cycled a few times and the nimh cells I put in some seem to be working. Can someone explain what a "pulse-charger" is and the advantages of same?

Bob

[Ian Field]

Different people have different ideas of what a pulse charger is.

Many commercial chargers have (or claim to have) a pulse phase as part of the charging cycle.

The theory is that supplying the charging current in the form of wide pulses interspersed with narrow pulses of discharge forms finer more even layered grain/crystals in the electrode material and results in higher capacity.

Apparently charging with smooth DC results in coarser grain that has lower capacity and promotes whisker growth and shorted cells.

When Television Magazine was in its first incarnation I had a couple of pulse chargers published. Both were modified SMPSUs, both used a resistor to limit the current from the regulation sensed output primarily to keep the switcher circuit in operation.

The prime mover for charging pulse current is a capacitor coupled diode pump from one of the SMPSU secondaries - there was a slight twist to the diode pump; the shunt diode is a Shottky barrier type to limit negative excursions that would occur with a slow reverse recovery type, the forward diode is a standard fast-recovery type - which at SMPSU switching speed still produces significant discharge pulses between the much more significant charge pulses.

The capacitor for the diode pump is selected by trial & error - increase until the cells are just about warm to the touch after a couple of hours treatment.

The pulse charger I've described is somewhat extreme and should only be used for occasional treatment of NiCd cells when they start to get a bit lazy.

Experiments with NiMh cells were inconclusive.

[Bill Wright]

Expensive 'intelligent' chargers meant for marine use increased the life of my 'leisure' batteries from two to five years. If the batteries had been heavily used whilst away then charged by the vehicle on the long journey home you could be forgiven for thinking that they were 'charged'. But at home the chargers would immediately put 15A into both

24V battery sets and that would diminish over the next ten hours to a trickle charge. The chargers have temperature sensors which are attached to the batteries.

Bill

[Bill Wright]

It's a dual purpose thing. As well as being able to charge a battery, if someone's heart stops you clip one electrode to each nipple and it gets them up and running around in no time.

Bill

[Ian Field]

My attempt at an ultra fast charger relied on temperature sensing for control.

For sheer brute force & ignorance I spliced a bridge rectifier into the neutral lead of a tabletop oven/hob and used a thermistor/window comparator to sense temp and switch current through the battery.

Only trouble was the current was so high the battery warmed up and tripped the temperature comparator in less than a minute. So as the battery cools the window comparator switches the current back on and so on.

As the battery charge got nearer full the heating time got shorter but the cooling time also seemed to shorten until at full charge I could hear the choke I'd included buzzing in short bursts.

Far from being a fast charger it took the 14h or more thats usual with cheap chargers - but it was the most capacity I've ever got out of NiCds.

[Bob]

A sort of tit-field thunderbolt? Bob :-)

[Ian Field]

You'd be up and running around if someone clamped crocodile-clips on your nipples!

[Peter Duncanson]

[Bill Wright]

Ah yes, 'Practical Television'! Blimey Ian, you must be knocking on a bit now old boy!

Bill

[geoff]

I remember buying a couple of editions of that

[Ian Field]

By "original incarnation" I meant before Technology at Home broke the camel's back, although I did buy the occasional Issue of PT when I was a

*LOT* younger.

ISTR a number of issues were also added to my collection by kindly benefactors.

[Albert Ross]

Oh don't talk to me about moles!

At first I let them get on with it as they were aerating the lawn but now I think I'll have to aerate the moles with a fork then roll their corpses flat.

[Paul Ratcliffe]

I've got both. The fact is that several sets of cells I've had to dispose of because they just do not hold charge to do the job they were purchased to do. This is despite being apparently charged 'properly'. Whether that is memory effect or something else I really don't know, nor care. It acts like memory effect.

[Steve Thackery]

The fact is that several sets of cells I've had to dispose of because they just do not hold charge to do the job they were purchased to do. This is despite being apparently charged 'properly'. Whether that is memory effect or something else I really don't know, nor care.

[PeterC]

The cheap PowerCraft combi drill seems to lose a full charge in 2 - 3 months (2Ah NiCad); the expensive Makita combi holds its charge usefully for 6 months + and gives much more use per charge (1.3Ah NiCad).

7DayShop has an offer on Sanyo Eneloop atm and judging by the packaging they're the 1500 cycle version.

[Ian Field]

Perhaps you should try getting a clue, and a decent charger.

MBQ

If you want to have a crack at designing one; google "burp charger", you'll only get a handfull of relevant hits but very interesting.

The pulse cycle is described as about 1S, most of which is charging current, follwed by a few mS rest period then a few mS discharge and a second slightly longer rest period before resuming charge.

One of my designs published in Television Magazine for NiCd batteries used a less sophisticated pulse arrangement but worked very well.

The XT SMPSU based charger worked a lot better still.