Acquiring a rechargeable battery for a 12 volt coffee maker

[UMD ENME472]

I am looking for advice and instructions on powering a heating element such as this <link> from let's say a rechargeable battery.

Assume the heating element requires 100 watts, therefore from the equation P=I*V the heating element would draw about 8 amps. I am interested in powering this device from a 12 volt battery either lead-acid or lithium-ion to support the portability aspects of brewing coffee, but am having trouble picking out the right battery specs for feasibility reasons.

For example a 12 volt battery at 5 Ah would generate 60 watt-hours, supplying on 6/10s of the needed power and heat, but I am unsure how long the battery would last? I'm guessing 3/4 of an hour because the battery needs some life left to recharge it? Again most of my observations are coming from assumptions.

I would like to supply enough heat to about 8 fluid ounces a water (enough for a small cup of joe) from room temp to about 195 F or 90 C. I appreciate any help and feedback. Thanks!

 

[MikeMl]

I dont know about yours, but my coffee maker draws about 6A at 120V, so almost a KW (720W, actually). It takes about 10min to brew coffee, so that is about 0.16kwH. If this is coming out of a 12V battery, the current would have to be about 60A for 10min. Lets see, a car battery would just about do it...

 

[Reloadron]

They draw between 120 watts and greater so figure 12 volts @ 120 watts = 10 amps. You gonna need a big battery. They are also more a "warmer" than a brew device.

Ron

 

[alec_t]

Welcome to the forum!

For example a 12 volt battery at 5 Ah would generate 60 watt-hours, supplying on 6/10s of the needed power and heat

.A 5Ah battery would (in theory) provide 8A for 5/8 (=0.625) hours. In practice, you would not want to run the battery right down, so you might get only ~0.4 hrs = 24 mins.

 

[UMD ENME472]

.A 5Ah battery would (in theory) provide 8A for 5/8 (=0.625) hours. In practice, you would not want to run the battery right down, so you might get only ~0.4 hrs = 24 mins.

Thanks, and I have also been looking int 11.1 volt Lithium Batteries because from what I understand the LiPO batteries can supply a higher current based on its' C rating. I'd like someone to confirm this. Please and thank you!

In theory the battery that I have spec'd in the Amazon link should provide enough current for the heating element, but I've read that LiPO batteries are dangerous, and I weary that the heat dissipated from the heating might damage the LiPO battery if the system is not insulated well.

 

[Reloadron]

Battery University will become your new best friend when it comes to batteries. Everything you could want to know and stuff you never wanted to know about batteries in all flavors, from selecting a type to charging and maintenance.

Ron

 

[Diver300]

A cup of water is around 300 cm3. It takes 4.2 J to raise 1 cm3 by 1 °C, and to go from room temperature to boiling you need (100 - 20 )* 4.2 * 300 J = 103,200 J. To allow for losses, and not running the battery flat, you should have around twice that as an initial estimate. 200,000 J is 55.5 Wh so a 5 Ah, 12 V battery should be enough.

A lot of those heaters are very low power and very slow, so insulating the cup can help a lot.

 

[UMD ENME472]

A cup of water is around 300 cm3. It takes 4.2 J to raise 1 cm3 by 1 °C, and to go from room temperature to boiling you need (100 - 20 )* 4.2 * 300 J = 103,200 J. To allow for losses, and not running the battery flat, you should have around twice that as an initial estimate. 200,000 J is 55.5 Wh so a 5 Ah, 12 V battery should be enough.

Thanks Diver300, and I've looked at these calculations before as shown from this excel sheet, but I don't understand how a 12 V, 5 Ah battery would transfer any of the energy into heating water. This is why I was questioning whether the 12 v, 5 Ah battery could support the above heating element because I don't know how else to heat water with a battery.

Thanks again.

 

[Reloadron]

The heating element originally linked to is **broken link removed**. My read on this one and similar 12 volt heaters is they all seem to work out this way:
Features

• Plugs Directly into Your Cigarette Lighter Socket
• For Use with Glass or Ceramic Containers Only
• Place Heater Coil Directly into Your Beverage
• CE Certified
• 120 watts
  
• 10 amp draw

They all seem to be 120 watt heaters or greater with a 10 amp current draw. In an ideal world a 5 AH battery would last 30 min. In reality that is not going to happen. Not with the linked to heating element or a similar one anyway.

I don't understand how a 12 V, 5 Ah battery would transfer any of the energy into heating water.

The energy from the battery is transferred to a heating element. Much like the elements in a toaster or the filament in an incandescent lamp the current through the resistive element generates heat. That heating effect is then transferred to, in this case a cup of water. Second Law of Thermodynamics: Heat moves towards cold. Leave your ice cream in a bowl on the table and it melts, leave your coffee cup on the table and your coffee gets cold.

Point is a 12 volt heating element that is 120 watts is going to draw 10 amps. Using a 12 volt 5 AH battery the battery will not even last 30 min (1/2 hour). Even a 12 volt 10 AH battery would not last an hour. The question becomes how much time the heating element will be drawing on the battery?

Ron

 

[UMD ENME472]

The question becomes how much time the heating element will be drawing on the battery?

This is very true, and that I have no idea towards figuring out Perhaps the best direction towards evaluating the feasibility of this is to actually test a 12 V, 5 Ah battery and time how long it would last powering the heating element at a constant temperature?

Also I have found a heating element that requires less watts about 85W from this <**broken link removed**>. Hopefully the Battery can sustain at least 20-25 minutes.

Back to Divers300 comment, I did such calculations, but I don't see how a 12 V, 5 Ah would boil water without using a heating element.

200,000 J is 55.5 Wh so a 5 Ah, 12 V battery should be enough.

 

[Diver300]

This is very true, and that I have no idea towards figuring out Perhaps the best direction towards evaluating the feasibility of this is to actually test a 12 V, 5 Ah battery and time how long it would last powering the heating element at a constant temperature?

Also I have found a heating element that requires less watts about 85W from this <**broken link removed**>. Hopefully the Battery can sustain at least 20-25 minutes.

Back to Divers300 comment, I did such calculations, but I don't see how a 12 V, 5 Ah would boil water without using a heating element.

I assumed that a heating element would be used, and I was thinking of the cup heater linked to earlier in this thread.

The energy calculation that I did took no account of the mode or speed of energy transfer. The calculation just compared the gain in energy by a cup of water with the energy stored in a battery.

In practice, fast transfer causes more losses in the internal resistance of the battery, while a slow transfer causes more heat losses from the cup to the surroundings.

 

[Tony Stewart]

I am looking for advice and instructions on powering a heating element such as this <link> from let's say a rechargeable battery.

Assume the heating element requires 100 watts, therefore from the equation P=I*V the heating element would draw about 8 amps. I am interested in powering this device from a 12 volt battery either lead-acid or lithium-ion to support the portability aspects of brewing coffee, but am having trouble picking out the right battery specs for feasibility reasons.

For example a 12 volt battery at 5 Ah would generate 60 watt-hours, supplying on 6/10s of the needed power and heat, but I am unsure how long the battery would last? I'm guessing 3/4 of an hour because the battery needs some life left to recharge it? Again most of my observations are coming from assumptions.

I would like to supply enough heat to about 8 fluid ounces a water (enough for a small cup of joe) from room temp to about 195 F or 90 C. I appreciate any help and feedback. Thanks!

If you use a well insulated ceramic coffee cup A LiPo battery might keep it warm for an hour then recharge when empty for the next refill. Attach battery to handle of coffee mug. Cut off battery at 3.3V for extended life. Use wireless technology at 21MHz to power the battery on your desktop from induction to a coil and diode on the mug. Or skip the battery and use iron wire wrapped around the mug and then fibreglass tape/epoxy /bondo insulated and use direct induction heater on the mug. Add decal to outside and no one will know you have a wireless coffee mug. 10 Watts should reduce the cooling rate of coffee if well insulated.

 

[alec_t]

I have found a heating element that requires less watts about 85W

As per Diver's calcs, you need ~55Wh to heat the water. With an 85W heater that will take 55/85hrs = 39 minutes, by which time the 5Ah battery will be flat.

 

[UMD ENME472]

Diver300, and anyone in general could you possibly help me understand how the mojoe coffee company was able to use a 15 V battery to make a portable coffee maker?

Attached is their indiegogo crowdfunding link. They seem to have solved the inefficiencies of heating water with a rechargeable battery. Thanks!

**broken link removed**

 

[Reloadron]

Diver300, and anyone in general could you possibly help me understand how the mojoe coffee company was able to use a 15 V battery to make a portable coffee maker?

Attached is their indiegogo crowdfunding link. They seem to have solved the inefficiencies of heating water with a rechargeable battery. Thanks!

**broken link removed**

Well I have been able to order one since 2014, but while I can pre-order I have yet to see a finished product. They are also still looking for "backers" should you care to invest. The point here is aside from pictures I have yet to see a working model. Now we can slice this and dice this in any way we wish but the formula Diver 300 presented has been around a long time. So while the Mojoe Coffee Company does exist they do not seem, as of yet, to have manufactured a product that works.

Ron

 

[audioguru]

The MoJoe heats the water in minutes. 2 minutes or 20 minutes??
It is fully charged from USB in how many hours??
Can one charge brew more than one cup of coffee??
After brewing a cup of coffee is there any charge remaining to keep the cup hot??