Battery type for backup power - Page 1
Forum section: electronics / general

author: AnonymousEngineer
author_rank: Newbie
timestamp: April 25, 2022, 09:36:17 pm
content: Hi everyone!I'm currently designing a system that is based on a Raspberry Pi with some accessories attached. This system needs a battery backup solution, that is reliable for a long time (10 years).The battery is only discharged during power outages, and will only have to supply the Pi with power for 10-15 minutes until the power is back on. The device will be installed in lots of different countries, so some places will have a stable energy source and others not so much.So I've been digging into the rabbit hole of battery technology, and I've officially lost the battle so I am asking you battery aficionados:What battery technology is best for:Keeping a 100% state of charge (Or close to it)Being able to go through many cyclesHaving a long lifetime.Generally it will be at room temperatureI know I might be asking for the "ideal" battery, and I am well aware that this might/probably does not exist!Based on my current knowledge it seems that LiFePO4 is a suitable choice?As anything in engineering its a matter of trade-offs and before I can make this decision I need help on what batteries technologies to look into!Thanks/AE

author: David Hess
author_rank: Super Contributor
timestamp: April 26, 2022, 12:58:17 am
content: What is the current or power requirement? Maybe a supercapacitor bank could be suitable?A 10 year operating life for a rechargeable battery is not easy to achieve.

author: Nusa
author_rank: Super Contributor
timestamp: April 26, 2022, 04:55:04 am
content: What's the upper limit energy requirement for that 15 minutes of downtime?Anyway, guessing it's not huge, my suggestion would be non-rechargeable Alkaline cells of whatever size/quantity required to meet double that goal. Combine that with a voltage alarm so they know to replace them before failure with off-the-shelf-anywhere-in-the-world batteries. If the backup is never needed, it should last the 10 years. If it is, replacements will be based on the frequency of use. Sometimes simple is the most practical.If you need longer than 10 years on the shelf, switch to primary lithium cells, at least for the initial delivery.

author: james_s
author_rank: Super Contributor
timestamp: April 26, 2022, 06:23:09 am
content: 10 years is a tricky requirement, but I think some good quality LiFEPO4 cells would likely do it. I know guys that have been flying A123 cells in model airplanes for 5+ years and still going and that's a pretty demanding application where they get fully charged and then drained in a few minutes delivering tens of Amps, over and over.

author: Gyro
author_rank: Super Contributor
timestamp: April 26, 2022, 09:27:48 am
content: It's a bit old school, but Cyclon SLA batteries (the cylindrical ones) are rated for 10 years in float charge, and up to 3000 discharge cycles. This is very conservative in my experience. Irrc, you can get them down to 2.5Ah (D Cell dimensions). You would probably get away with 3 cells and an LDO (or maybe an efficient buck from a single cell).LA is still probably the battery technology that is most happy with float charge.They were originally made by Gates, then went to Hawker Energy and currently EnerSys...https://www.enersys.com/en-gb/products/batteries/cyclon/cyclon/

author: Faringdon
author_rank: Super Contributor
timestamp: April 26, 2022, 09:42:42 am
content: Yes, indeed, agree with Gyro...Lead Acid (SLA) is used in Fire Alarms, certainly in UK.LiFePO4 sounds like the best of the lithiums. Its the most robust.Its only 3.2V... so if you can use just one cell, and boost up if needed, then thats good........you dont want to have battery balancing problems if you can help it....where one bad cell takes out the whole battery.Of course, if you need more power, you can pllel cells, and then if one cell does go bad, then you can switch it out.....having said that, i suppose you can switch out a cell in a series stack too.NiCad and Pb acid are knownn for being very robust and can handle permanent trickle charge without going too bad.......also, Nicad is good with very cheap chargers that would tend to overcharge more delicate lithium.Think nicad is illegal in some countries, but not for all applications.