Battery powered stir plate for lager starters in fridge?

[SanPancho]

i think that pretty much sums it up. i do around 75% lager brewing, so id prefer to keep my starters in lager temps, not room temp. but SWMBO isnt gonna be cool with a full stir plate and power cord running out of the fridge. and i cant fit the stirplate into ferm chamber at same time i have a beer fermenting, so i figured i'd go for a battery powered setup and stick it in kitchen fridge.

the idea? same cigar-box stirplate i already have, but with a 6-12V fan and a battery power source. maybe someone who's more electrically knowledgeable can tell me if this is feasible?

this is going to be for something small, like a 1/4 to 1/2 liter starter at most, since i do mostly 1 gallon batches, so it doesnt need to be super powerful. assuming i get the smallest setup, which would be a 6V fan, drawing .25A, and i'd like to keep it on for 12-18 hours. thats 1.5Watts, at 18hours, is 27 watt/hours?

how do i figure the battery size to keep it going? and do i have to keep it a similar voltage battery?

any advice appreciated.

 

[IslandLizard]

How about a small adapter/wall wart? The skinny flat wire will likely go between the frame and door gasket.

But... 38°F is too cold for lager yeast to grow, it will go dormant instead.

 

[BigFloyd]

Most of those computer fans are 12V, but you'll want to run them at a lower voltage to knock the speed down. I use a cheapo eBay step down voltage control on my 12V wall charger to do that. Instead of a battery, I would suggest a wall charger and let the fridge door close over that tiny cord.

BTW, Why do you not want to run your lager starters at room temp? The goal is to culture a yeast colony for the desired number of cells, not ferment a beer to drink. I haven't yet heard any of the yeast gurus suggest that there's any benefit to multiplying lager cells at 50*F vs. 74*F.

Also, if you're doing one-gallon lager batches, you'll probably be close to the target cell count with a vial or smack pack and no starter.

But... 38°F is too cold for lager yeast to grow, it will go dormant instead.

+1. If you're running the fridge without a controller like an STC-1000, it'll be too cool to get cell growth.

 

[SanPancho]

a wired/plugin unit is not an option. has to be battery.

the yeast i use will multiply and ferment, albeit a bit slowly, at 45F, which is where the warm spot in our fridge is. yes, i can run the starter at room temp, but that's not what i want to do. i want it to run at kitchen fridge temps.

i reuse yeast slurry, so cell count isnt really an issue. what im trying to do is re-energize the yeast so they are ready to go when i pitch. my experience puts this in the 12-18 hour range at these temps.

it works for me. no off flavors, no stressed yeast. short lag phase. i just want to figure out how to do it under battery power.

any help with the battery sizing would be greatly appreciated. im not entirely clear how to calculate that part of the puzzle.

 

[MaxStout]

You will need to determine the needed battery capacity, based on the current draw of the fan. Most rechargeable batteries are rated in milliamp-hours. Many PC fans will be stamped with the current rating, typically in milliamps.

For example, if your fan draws 100mA, and you want to run it for 24 hours, you will need a capacity of at least 2400 milliamp-hours (2.4 amp-hours). This is an oversimplification and does not consider power loss due to potentiometers, voltage regulators, etc. Keep in mind that a battery's available capacity may be less at cooler temps.

Get a small sealed lead-acid (SLA) battery, which you can also find at motorcycle or boat shops.

 

[Stealthcruiser]

a wired/plugin unit is not an option. has to be battery.

Why not?

If you are going through the hassle to set up a battery powered setup, you could:

Get a receptacle, that screws into a standard bulb socket, pull the refrigerator light switch from it's mount, and jumper the circuit.

Then use your standard stir plate setup, like it was sitting on the counter.

I would think it cheaper than tracking down a battery rig that you might worry about going dead on ya'.

Downside: no light in the fridge for a few days.

If you just gotta' have battery powered, scope out the ratings for batteries, ( the backup ones), for home alarm systems.