Hot food Case for Meals-on wheels

[davido]

I am designing a hot box for delivering meals-on-wheels.
I have built an insulated case of stainless steel, that will hold the required number of meals. The prototype is using refrigeration heater cable, on 240v/195W which produces enough heat to keep the case at 70 deg. c. .

My problem is that I need to run this with a small 6v rechargable battery. I can get a 6v battery with 18ah, but I need to find some low resistance cable that will do the job and run on the 6v battery. I may be able to go to a 12 v battery but this increases the size of battery and weight. I need to keep the battery size and weight low.

 

[nbucska]

6*18 = 108 Wh. If you had 100% efficiency, you could heat
it for 1/2 hour.

Why not use butane or the cooling system of the car ?
<nbucska@pcperipherals.com>

 

[BrianR]

Have you considered using a static inverter to convert 12VDC to 230VAC. Run it off the vehicle as long as practical then of a battery if you have to leave the vehicle. I'd think the battery will suffer rather badly though driving a load like that. Static converters are not very expensive.

 

[nbucska]

BrianR : Even for the car battery 17 A seems to be excessive.

Would'n butane be simpler ?
<nbucska@pcperipherals.com>

 

[jarvis]

How about a 12v heat lamp, that should heat up an insulated stainless box, plus provide lighting. Hook it up to a thermostat for power conservation.

How about using nichrome wire as a heating element and just finding the right length based on wire size and such. I'm planning on using some myself on drains and covers for fish transport tanks to keep them thawed out in the winter.

 

[johncrabtree]

I suggest the following:

1. Take some time to make the best possible insulation. A little effort here will be well rewarded by reduction in heating energy requirement.

2. Consider adding thermal capacity to the inner box (possibly use bricks like in night storage heaters). Then use your present element to pre-heat the box. During delivery runs a thermostatically controlled small wattage element run directly from the car battery will suffice.

 

[davido]

Jarvis
Where can I get nichrome wire and how does it work?
From Davido.

 

[jarvis]

davido

Nichrome wire is a commonly used resistive heater wire. It acts as a resistor and gives off heat. It is available in many sizes and any length you want. You choose the sizes based upon your available voltage and current and your application. One place you can get it is...

http://www.morelectric.com/nichrome.htm

Cost is about a $1 a foot and I'm sure they will help you choose a size if you can't figure it out from the chart they have.

 

[jbartos]

Suggestion: It appears that a combination of the better thermal insulation for your box, the suitable resistive conductor, and the more efficient modern batteries could satisfy your meals on wheels thermal requirements.