>  ...  NiCads  ... LiIon batteries ... charging requirements.

> ... current drawn monitoring circuit that could visually indicate that th=
e
> heating element is working.

> The heating elements are 240VAC / 60 W.

That was more comment than questions.
Comment is good :-)
LiIon are extremely easy to float.
Supply via a current limited voltage source.
Current limit is set to C/1 max ie mA max =3D mAh capacity of cell.
Constant voltage source is set to 4.1 V or 4.0V for a single LiIon cell.
Real world equipment uses 4.2V to get all possible capacity but then
you need end point termination based on current and temperature
compensation. Using say 4.0V will be nicely gentle on cell and extend
life.
NiCd are robust but not spoken of in polite circles these days due to
Cadmium content. OK to use if disposed of properly.
NimH are OK if kept topped.
Self discharge rate is high.
LSD =3D low self discharge are getting very good.
LSD: =A0NEW version of Sanyo Eneloops are excellent.
LSD: =A0GP Recyko are at least very good and may be excellent.
NimH can be charged to end point of say 1.35V to1.4V per cell with a
sharp cutoff voltage. Zener is not sharp enough.
___________

A circuit is always useful - even if "apparently" trivial.

There are many ways to monitor current including eg series current
sense resistors, current transformer, hall sensor, proximal thermistor
heat sensor etc.

An "easy enough" flexible method is to place the diode side of an opto
coupler in a diode bridge.

Load circuit connects to  AC terminals of bridge
Resistor in series with opto input
Say 3v3 or 5v6 zener across bridge DC terminals.
Opto driven from zener.

When element runs the zener has DC volts across it =A0and opto is driven.
With 2 elements working you now have 2 isolated floating outputs to
use any way you wish. Any of LEDs, alarms, AND for one element detect,
OR for at least one element going, ... all of these. Cost per element
is opto, zener, 2 x resistor plus whatever processing you decide on.

Failed OC zener will probably destroy opto BUT this will trigger alarm.

With 240 VAC 60W element current is 250 mA.
As described above zener at say 5v6 dissipates 5.6V x 0.25A  =3D 1.4W so
not trivial.
3V3 dissipates 0.8W+ so hardly better.
Not a vast amount of energy but worth noting.

Using transistor be junction as turn n sensor gives say 1V x 0.25A =3D
0.25W. This can still drive an opto and reduces overall power.

Using opamp as current sense resistor monitor can use ~=3D 0 power.
_________________

Note that Hall cell can give you isolated current sensing in a wire.
So can current transformer.
Questions ...?


=A0 =A0 =A0Russell McMahon






>  ...  NiCads  ... LiIon batteries ... charging requirements.

> ... current drawn monitoring circuit that could visually indicate that th=
e
> heating element is working. Another option may be to put another
> temperature sensor on each element but I was hoping for a simpler option.
> The heating elements are 240VAC / 60 W.

--=20
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.