without seeing these batteries, its not worth a friggin reply. I just promote OP doesnt have 5kw LI batteries and not even 500 and I even doubt 50W

 

I only drink coffee in the morning
But yeah, seems like the best solution. I would however need to make the device large enough so that the electronics are separated from the heating element(s), assuming no cooling. Alternatively, I could make a case with a large heatsink and some extremely high power delta fans to cool it off enough for longer periodic use. (Generally I'll be using it to discharge around 1500-2400W in 15-60min.)

A heating element like this one requires 220V. How can I up the voltage without using a transformer? I need variable voltage above that of the LiPo batteries. MOSFETs in series?

I were planning to build some heaters to maintaining the temperature for the vegetables when the winter that the foods on the table were easy to getting cold, but I'm not sure what are the best way to do, using power resistors or heating wires, and how to build the interface for the dishes.

I'm hoping to build maybe 5 heaters for 5 dishes, they will be as following:
4. Top -- foods
3. Dish
2. The interface for dish.
1. Bottom -- heaters

There are over 6 months the foods on the table easy to getting cold in Taiwan, so I think that is the way to waste the power to maintaining the temperature for foods.

 

I were planning to build some heaters to maintaining the temperature for the vegetables when the winter that the foods on the table were easy to getting cold, but I'm not sure what are the best way to do, using power resistors or heating wires, and how to build the interface for the dishes.

I'm hoping to build maybe 5 heaters for 5 dishes, they will be as following:
4. Top -- foods
3. Dish
2. The interface for dish.
1. Bottom -- heaters

There are over 6 months the foods on the table easy to getting cold in Taiwan, so I think that is the way to waste the power to maintaining the temperature for foods.

Hi,

You are building a heater for vegetables that you have cooked? Will you be getting power from a wall socket or locally mounted battery? That's how I understand it.

Plates to eat from or plates for keeping prepared food warm?

In any case, I would:

- Get some good quality plates of desired size
- Buy Aluminium sheets and cut them in round sheets to fit under the flat section of the plate (Approx. 1mm thick)
- Get low power but long heating coils and place them under the Aluminium sheet in a "wirl" (Like this)
- Make a simple variable (step) power adjuster with pre-tested increments

 

without seeing these batteries, its not worth a friggin reply. I just promote OP doesnt have 5kw LI batteries and not even 500 and I even doubt 50W

I never said that afaik?
My LiPos can discharge 5KW+ continuously, but only contain 40-80KWh of power each.

I have several of these for example, which I always use in series. They can discharge up to 1596W continuously fully charged and 1254W continuously when almost "empty" (each).

 

I built a TL494 power supply once with large 500VA Toroid.

I designed it for 250 Watts but found I can run it at about 400 Watts.

At 400 Watts, the whole cabinet gets hot even with ventilation.
The thick wires heat up considerably, the electrolytic caps get hot and the rectifier needs cooling.

I can know 500 watts (at much higher voltage so the Amps are lower), because I dealt with it.

5 kW at 7 volts or 14 volts? You have no idea about the kinds of cables and connectors probably.

For 500 Watts at around 80 volts, you need pretty decent cables + large screw terminals.

Even a 400 volts cable for 5 kW is quite heavy.

Seriously, 7600mAh can produce 80 kilowatt for one hour?

I enjoy discussing with you, but your maths are incorrect, and you dont properly understand the kinds of cables/connectors required for kilowatts at low voltage.

Think of an arc welder cable, thats what you'd need- it just doesnt match your batteries

 

First, back to basics. All wasted energy turns into heat. There is no such thing as a small 5000 watt heat system. I think MrChips was out of line to call you an oxymoron. (MrChips will get that joke, even if you don't.)

So...the first thing to design is how to get rid of 5000 watts. We do that with fans in the Air Conditioning/furnace business.
3.413P = 1.08 CFM dT
For 5000 watts, 15801 = CFM dT
For 200 CFM, the air will heat up by 79 degrees F

For water, one watt-hour per hour produces 3.413 B.T.U.s of heat.
A B.T.U. is defined as the amount of energy required to raise 1 pound of water one degree F.
5000 watt hours per hour times 3.413 BTU/W = 17065 pound degrees of water (in Fahrenheit)
For 100 degrees change in water temperature you will be heating 170.65 pounds of water (20.5 gallons) for an hour.
If you want to discharge the energy as steam, calculate the distance from ground water temperature to 212F and figure in 970.3 BTUs per pound of water to turn it into a gas.

Whew! That was a lot of math and looking up constants!

Now for the simple part: What do you want to use to burn the electricity? Car headlights? Wirewound resistors? Nathans Coney Island Corn Dogs? Fan motors that are busy cooling themselves?

There''s a start, but I'm getting tired now. Most of the other helpers can finish this set of calculations.

So theoretically I will need 15801 CFM to cool 5000W down to a reasonable level?

Also: steam! Sounds like a very interesting option. I could make a closed-system water boiler with a fixed pressure valve to let steam out and into a condenser which gets the water back to liquid state and puts it back into the container for boiling. Using valves gets me steam outlets which I can have in parallel to condense the directed steam over a large surface area packed tightly.

I should use a cooling system to get the condensing area at an as low non-water-freezing temperature, right?

 

I built a TL494 power supply once with large 500VA Toroid.

I designed it for 250 Watts but found I can run it at about 400 Watts.

At 400 Watts, the whole cabinet gets hot even with ventilation.
The thick wires heat up considerably, the electrolytic caps get hot and the rectifier needs cooling.

I can know 500 watts (at much higher voltage so the Amps are lower), because I dealt with it.

5 kW at 7 volts or 14 volts? You have no idea about the kinds of cables and connectors probably.

For 500 Watts at around 80 volts, you need pretty decent cables + large screw terminals.

Even a 400 volts cable for 5 kW is quite heavy.

Seriously, 7600mAh can produce 80 kilowatt for one hour?

I enjoy discussing with you, but your maths are incorrect, and you dont properly understand the kinds of cables/connectors required for kilowatts at low voltage.

Think of an arc welder cable, thats what you'd need- it just doesnt match your batteries

I'm not familiar with the PSU circuit, but a 400W PSU gets considerably hot in a ventilated cabinet? My Corsair AX760i PSU barely uses its fan when I'm drawing 500W. I know it's a premium supply, but it tells me something about the difference in efficiency.

Did I say that about the Wh? I will look over my posts and edit them (And mark the edits if so). I have LiPos that I use in parallel and series which can handle 5KW continuous draw but which are only around 40-80KWh in capacity. (These are half a kilo heavy packs you can hold in your hand.)

EDIT: Ah, post number #9 in the thread, where I said I would use it to discharge XXXX-XXXXW in 15-60 minutes. What I meant was obviously those amounts continuously over that time, as far as the batteries can deliver. I used W, and not any W't' specification.

 

Well, before Manfred asked for help on the forum he probably used incandescent light bulbs as loads but he had to stop because he was blinded by the light.
Then he used an electric motor but it revved up like a deuce and he had to shut it down.
Then he used the power to run his go-kart Mozart but while checking out the weather chart found it wasn't safe outside.

....do I need to continue??

Post of the week!

 

sure, a 1/2 kilo battery has 80 KWh.

you can run a 80 KW motor for one hour! nice battery.

It is Watt hours perhaps.

 

sure, a 1/2 kilo battery has 80 KWh.

you can run a 80 KW motor for one hour! nice battery.

It is Watt hours perhaps.

Dang, that's where the error is at!
Yes, Wh, not KWh.

I'm unable to edit those posts...

Sorry about this.

 

Why would you want to discharge them at high current? Its no good for them.

Also I dont know if an answer to your question can be found- most efficient way to waste power?

Efficient how? How do you define that efficiency?
In Phyics I learned each factor must be specified in a scientifically valid way, not in a maybe-couldbe, emotional or Apples for me, Pears for you way.

when you cant define a factor in physics you cant describe the system in a valid way, and so you cant derive correct formula.

 

Why would you want to discharge them at high current? Its no good for them.

Also I dont know if an answer to your question can be found- most efficient way to waste power?

Efficient how? How do you define that efficiency?
In Phyics I learned each factor must be specified in a scientifically valid way, not in a maybe-couldbe, emotional or Apples for me, Pears for you way.

when you cant define a factor in physics you cant describe the system in a valid way, and so you cant derive correct formula.

Well, my purpose is to make a device that can do discharging of high amounts of electrical power in the smallest casing practically possible.
If you need to drag this outside that and into theoretical insignificances, you are either in need of this information because you're going to write me 100 pages of research on this or you're just... Doing what? Others have been able to answer me here because they've understood the goal and considered the information supplied.

 

Ah OK, smallest casing, all clear. I hope you get along with your project.

 

And it only took 32 posts to arrive at a design goal.

 

And it only took 32 posts to arrive at a design goal.

It took one, I said it in the first post:

Oh - And I intend to make it 100% powered by the LiPo connected and as small and light as possible - Field convenience.

 

Fair enough, so you did. Any reason you couldn't just use 5 x 1000W light bulbs? I like bulbs because they are cheap (compared to resistors), give visual feedback, and are purpose-built to dissipate heat. A downside is that they have a low resistance until they heat up.

 

Fair enough, so you did. Any reason you couldn't just use 5 x 1000W light bulbs? I like bulbs because they are cheap (compared to resistors), give visual feedback, and are purpose-built to dissipate heat. A downside is that they have a low resistance until they heat up.

1000W
I didn't think of the special lamps from Osram and so that put out this much power. You're right, it's easier to use light bulbs with some cooling. It can be handy as a light source too.
Will be looking further in to it. Thanks!

 

You are building a heater for vegetables that you have cooked?
Plates to eat from or plates for keeping prepared food warm?

Yes, the food were cooked already.

In the winter when the room temperature under 20 ℃/68 ℉, the foods will get cold about 20 minites from the hot foods put on the table, so if we eating too late, eating the cold foods is not a good feeling in the Winter, and i always like to eat slowly.

Will you be getting power from a wall socket or locally mounted battery? That's how I understand it.

I won't use any battery, but i just saw takao21203 talking about the PSU, maybe i can use it for the heaters.

Using AC110V heater as dry machine or using power resistors with 12Vdc.

In any case, I would:

- Get some good quality plates of desired size
- Buy Aluminium sheets and cut them in round sheets to fit under the flat section of the plate (Approx. 1mm thick)
- Get low power but long heating coils and place them under the Aluminium sheet in a "wirl" (Like this)
- Make a simple variable (step) power adjuster with pre-tested increments

Thank you for your suggestions, i will try to figure out.

 

So theoretically I will need 15801 CFM to cool 5000W down to a reasonable level?

Big, fat, NO.

15801 is the CFM times the temperature difference. If you blew 15801 CFM across this heater, the exiting air would only be 1 degree warmer than the entering air. If you want to go from 68F to 160 F, 15801/92F = 171.75 CFM. If you have all kinds of surface area radiating most of the heat, the required air flow becomes even smaller.