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York · 30th September 2007, 17:48

Quote: (Originally Posted by nigelh)

The cells are always current limited or the output voltage would be set by the chemistry not the quantity of fuel.
The simplest cct would just be a resistor across the cell, say 80R and the voltage read would be proportional to the current and thence to the fuel supply.
Sadly the cells are also quite good thermometers so some sort of compensation is needed and a bead thermistor stuffed down the back of the cell works for Teledyne. They keep playing with the circuit. The first ones I took to bits had the thermistor on the top of the PCB well away from the cell.

I don't think the 10K load is significant. They just want you to use >10K so there is no significant loading.

The cct came from

the write up is here.

I agree 100% on the current limitation, no idea where that expression came from to describe the aging effect. I believe "diffusion limited" may be more accurate (as electrolyte depletes, and product buildup occurs on the anode), but that would be another discussion.

So you are saying there are historic reasons for the 10K load, and it could be omitted without too much of a negative influence? I know the VR3 includes a 100K load and is used for the R22s - supposedly successfully. We were looking at EMFs and their influence, not sure we came to a conclusion.

Thanks for the link, a nice write-up.

This is a great discussion folks, I learned a lot! thanks!!!

Joerg

30th September 2007, 17:48	#15 (permalink)
York probubbly not Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Mar 2005 Location: Bristol, UK Posts: 118	Re: sensor load and life expectancy Quote: (Originally Posted by nigelh) The cells are always current limited or the output voltage would be set by the chemistry not the quantity of fuel. The simplest cct would just be a resistor across the cell, say 80R and the voltage read would be proportional to the current and thence to the fuel supply. Sadly the cells are also quite good thermometers so some sort of compensation is needed and a bead thermistor stuffed down the back of the cell works for Teledyne. They keep playing with the circuit. The first ones I took to bits had the thermistor on the top of the PCB well away from the cell. I don't think the 10K load is significant. They just want you to use >10K so there is no significant loading. The cct came from the write up is here. I agree 100% on the current limitation, no idea where that expression came from to describe the aging effect. I believe "diffusion limited" may be more accurate (as electrolyte depletes, and product buildup occurs on the anode), but that would be another discussion. So you are saying there are historic reasons for the 10K load, and it could be omitted without too much of a negative influence? I know the VR3 includes a 100K load and is used for the R22s - supposedly successfully. We were looking at EMFs and their influence, not sure we came to a conclusion. Thanks for the link, a nice write-up. This is a great discussion folks, I learned a lot! thanks!!! Joerg
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