using car battery as temporary backup power

I have been printing great stuff with my folger kit but lately power blinks have been bad. They usually don't last too long but they allmost allways mess up the print. I'm looking for a low tech way to set up a backup power supply. I have to a car battery, is it possible to connect it to the power supply of the folger with a relay that closes the circuit when on main power?

A 3s LiPo/1500mAh ( or bigger ) battery would fit better in the voltage-window and they are widely available in RC-hobby shops or online for a few bucks.
Best match would be a 4s LiFePO battery, but they are harder to find.
You should have some experience with Lithium batteries regarding balancing and max. charge current a.s.o.
-Olaf

No need to use a relay, you can keep the car battery on charge all the time, the way a car does. If you make sure the battery is fully charged to start with, you could use a LED power supply turned up to about 13.4V to power the printer and keep the battery charged.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Remember a lead acid car battery vents. You might want a sealed battery.

Thanks everyone really good stuff.

I should have mentioned that I live in Costa Rica so shipping things is a much bigger ordeal. Soon I should have some money to ship a bunch of printing related stuff, including a solar kit to go with a bigger battery system. But until then I need some sort of hack....

I think I might go with dc42s advice, it looks like I can use the same power supply that came with the printer. 12.6 volts is the optimal trickle charge rate I believe, so with 13.4 keeps the printer going. I am a little worried when the print ends it will be too much for the battery, but I could just disconnect it. Making/ Hacking some sort of charge controller circuit would be Ideal.

If I could find or hack some lithium battery somewhere it would do the trick and be a bit more convenient, although the car battery would keep it going through much longer blackouts.... And I would still need to figure out some sort of charge controller set up.

Depending on how long you want the printer to survive a power outage, a 12V motorcycle or SLA battery should suffice and will be be smaller and lighter.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Ive got insanely good news. I remembered my old gaming laptop that died. I tested to see if the battery holds a charge by using the same crazy laptop that it belongs to. Stayed on after i took the cord out for a minute, didnt go off. gonna see how long it lasts after i charge it for a while. Its 5200 mah 7.3 watt hours.

Its rated for 14.8 volts. If I run the power supply at a lower rating will it trickle charge the battery while still being able to run the printer without ever overcharging the battery?

14.8V means it´s a 4s battery ( 4x 3.7V ). Fully charged it would have 16.8V, but never less than 14.0V
It wouldn´t be useful to keep it in 4s configuration unless your power supply can supply anything from 14.8 to 16.8V.

Better dismantle it and cut off one bench of cells to make it a 3s battery. ( Without BMS though)
That´s where the experience comes handy! Do at your own risk. Although the 16850 laptop cells are less critical than these RC-hobby soft pouches.
If you don´t like the lithium idea, use the motorcycle SLA stuff, you have scooters in Costa Rica for sure...
-Olaf

Thank you Olaf exactly what I needed too know...

Too bad I have to loose the battery management system AND some capacity. Plus I was gonna print a sliding mount for the case, Now it looks like a get to make moy own case altogether .

Now time to pry....

Ok battery open. All have more than 4.12 volts!!!! not bad for a battery thats been stagnant for nearly 5 years....

Could I use the battery management system from another battery to control the charging?

OK I just opened up another toshiba battery rated at 10.8 volts. 2 of the 6 batteries had more than 2.5 volts in them. I got the manager circuit as well.

so now I have 10 batteries,I should be able to hook up 9 in 3 banks to make 12 volts and even more capacity. This is looking really good now everything is coming together, but i still need to figure out how to hook up this charge circuit....

I kinda wish i paid a bit more attention to the wiring on the Toshiba battery before I ripped it apart...... I could have easily copied it

the toshiba had a little diode sandwiched between 2 batteries.

Be careful with mixing batteries from different packs. Can you check each block individually for real life capacity under a given load?
I´m afraid the 2.5V cells are no longer useable.

Do you have a cellphone charger? This would be a good single cell charger to get all cells to the same level. before putting them together.
-Olaf

I had this on my mind i still need to test the other 2 batteries properly. they might wig out when they get frully charged. I have a camera battery charger that lost its partner. its rated for 4.2 output so it should work perfectly. I also know that even if all the batteries are fine and one has less voltage it can drain more than the other and thus die, unless it has a controller built to monitor that. So 'its better they all have the same charge.

I've mostly been researching this whole time how to deal with the charging circuit. What I am thinking right now is that I need to find a charger for an appliance that uses lithium ion batteries in a 12 volt configuration. From what I'm gathering if I used a lead acid battery charger it would charge fine but never get to 100%, which should be ok, but I need confirmation.

I'm still not sure what would happen if I hooked them up to the circuit i got out of the Toshiba battery. Do those things handle everything related to the charge or is part of it handled by the laptop itself?

I have discovered that I can use the circuits built into mobile phone batteries hooked up in series with the batteries. Will let everyone know if it works, and if it does then ill probably document it because its the perfect solution to this problem.

Edited 1 time(s). Last edit at 08/08/2015 07:26PM by nck2000.

The voltage of the pack should match the voltage of your printer PSU. Otherwise you´ll see huge balancing currents when you connect them. Some PSU are not happy with reverse output current, most don´t care. The safest way to charge the pack ( once the cells are matched ) is to charge it with the printer PSU and leave it there. They won´t get fully charged but they don´t have to be balanced either.
-Olaf
PS: The circuits from cell phone batteries are usually not able to be chained into larger packs. You would need three individual power supplies for three circuits. ( Galvanic isolation is the keyword here )

Just a word of warning because it seems to me you are on your way to having a major accident. Lithium batteries require specific charging procedures and are much more fire-prone than typical automotive batteries.

In any case, I would never recommend connecting either of these battery types directly to an LED switch-mode PSU, you are most likely to burn the PSU, or short the battery, or damage both the PSU and the battery and hurt yourself in the process, or even start a fire.

If you want a small UPS for your printer just buy a small one for a home PC from a reputable vendor. Having a safety hazard in your home just to save a few $ is not worth it.

In a cars maximum 90Ah to 100Ah battery is installed for power backup. you can use car battery for temporary backup power but should be remember the load capacity is not more than ampere rating.