Running a Cubecell AB02 on AA Batteries

#1

As much as I would prefer using LiPo’s this little project will have no way of charging the batteries, they will be in an isolated enviroment and suffer from all sorts of temperature issues.

Dry cells seem to be the only stable way to resolve a few of the battry headaches but I also need to maintain low power draw.

What I am looking at is using 3 X AA cells giving me 4.5V in total.

If i attach them to VIN then if the battery is not present on the battery connector the charge LED will stay on, I also want to be able to use the battery voltage sense circut to gen an idea as to what the battery level is.

I was thinking about cutting the track from the charge circut to the battery connector as an option but not sure as yet if this will cause other issues like stopping the vext from working.

Any sugestions?

#2

Try 2XAA directly to the 3V3 pin

#3

I had thought about that. I suspect that it may work for a short time but the voltage will drop prety quickly even though the battery capacity is sill reasonable. A higher voltage will provide more usable capacity for the system than the lower voltag. The cubecell may be Ok with the lower voltage but the sensors I am using would become unstable.

The other issue is I think the battery sense connection would need to be cut and changes to sit on the 3.3v rail because I beleive from what I have seen in the chematic its connected to the battery connection.Althought it also looks like there is a pad underneath that will make this and eaiser task.

#4

Have you looked into Lithium-thionyl chloride batteries? e.g. 20AH in “D” size, 3.6v with a flat discharge curve (3.6v to 3v) and significant capability for low and high temps (0-200, although I thought they could go below freezing). This is the kind of battery (in 1/2 AA, 1.2AH form)that the cubecell 1/2AA board was designed for.

You won’t find them in a store, but ebay will sort you out.

#5

They are an asweome battery and may be the only other option. I would still need to look at cutting out the charging circut as if someone turns up with a laptop to reprogram or dump the data on the units im not sure how they would like being charged given they are primary cells. I also looked at lithium-titanate’s as they are a rechargable battery with a low temperature rating but really expensive.

#6

We should ask Heltec about the specs for the module – their sheet says max 3.5v but the main datasheet I found on the internet for the ASR6501 is higher (3.7v max recommended, with 3.9v as the Must Not Exceed). They presumably have a reason for downrating it, but I’ve successfully powered the module without a regulator, and bypassing the onboard regulator, from LiFePO4, and LTC has similar max voltage.

If you power the board directly then the USB connection isn’t an issue, AFAICT, although it does reset when disconnecting the USB.

#7

Yea, the earlier boards I had a look at altering the LiPo charge controller and ended up lifting one of the pins for a project. Seems to have worked and as far as i know is still chugging along.

I just had a look at the ER34615. D Cell sized battery with 19Ah capacity at 3.6V!!! Down side is you can only pull 400ma from them.

#8

SAFT LS14250 1/2AA Lithium batterij 3.6V is for sale in NL in an online batteryshop for E 3.99