batteries that can take numerous cycles?

[cadillackid]

as I build out my glass cockpit for the redbyrd.. I am facing a unique challenge. I am using a raspberry pi to do my switch panel..



when I shut the bus off, the touchscreen will go off on a timer override, buit I want the computer to stay on for 'X' amount of time to stay awake and not have to be shutdown and rebooted if im say running errands and such.


the computer pulls a couple watts when it goes into idle mode.. so over a long period of time that would run the bus batteries down if I left it on..


my thought is to have a second much smaller battery that the computer runs off of.. I wantto be able to cycle that battery down somewhat low until a GPIO would detect low battery and execute my shutdown sequence and kill the computer till I powered it back on..


my trick is in findinfg a battery that can be run down to say 50-60% and then stored that way.. as this would happen when the bus is parked for long enough to trigger the shutdown.



the plan is to have a dash switch for this but I know ill forget to use it so I want a battery that works with my forgetful brain..



the other thing is the battery will get stored cold... I live in ohio.. I do plug the bus into shore power so I could keep a maintainer on it when shore powered.. but again things happen.. power goes out at the storage place.. I forget to connect it.. etc...


do I just need to put in a really oversized battery that I would only drop to 80% and then charge back up ?


if I go lithium I want a battery that is automatic.. something with built in BMS....



is what I want to do just hard on batteries?

[joeblack5]

Hi Chris, may be look into a used DeWalt 18v battery with 12 volt charger.. the older 18v ..not 20 volt have an integrated bms so will shut down by it self.
Hack into the 18 volt battery with two wires and then a15 to 12 or 5 or 3.3 whatever is convenient.. I like insulated DC DC converter but that might be overkill.

Johan

[cadillackid]

What a cool as heck idea I never even thought about tool batteries.. a regulated supply off of the battery would run the computer. Wonder if the battery provides output if it’s in the charger but you unplug the charger from the AC power.. I have a couple of those 18 volt battteries and the charger as I had an 18 volt drill that died and stilll have the flashlight that came with it

[joeblack5]

Nothing lost if you already have them... I normally uocycle old labtop batteries.. the 16850 is the same as in led flashlight, at least my cheap ones,

You probably could crack the laptop bms protocolanf so charge with a simple 19 volt labtop power supply.

What voltage does your computer run off? Maybe just 2 4.2 v cells in series. Maybe if you computer has a a/d converter you could have it sample its own batteries and shut down the batteries and itself.
Have fun Chris.

[cadillackid]

My computers are MAC so who knows what voodoo apple does they are Wierd.

I like the idea of built in BMS so I don’t need to be concerned if the computer locks up that I overcharge the battery.. if the battery is full I want it to stop taking juice. I experimented with various portable power banks but they seem not to be bi directional . They either take juice in the charge port or give it out and not both. I could probably build a power supply with a low decay rate to allow for a relay to switch from battery to bus power and back again. The switch time short enough that the machine stays powered. The raspberry pi just needs stable 5 volts. No rocket science there to make a step down supply for it

[Diverdude0075]

Lithium ion batteries can be run to 50% without damage and do a lot of charge cycles. AGM and lead acid are more susceptible to damage when drained too low.

[Mercuric Mind]

This may not be the most cost effective route, but there are LTO batteries that have lots of cycle life. The voltage drops over the charge cycle and you would need to use a voltage regulator to get proper voltage. This is if you want to go the route of making a battery. Will Prose has some u-tubes about this type of battery.