Discharging a large 2V lead acid battery.

[Mosaic]

And the resistance of that heater changes how much as it heats?

 

[tcmtech]

Electric hot water heater heating elements make excellent high power 4500 watt resistors the one in the photo costs only $8. I have 4 heating elements connected together to my 12 KW project I originally built 20 years ago. If I only use it 20 seconds each time water circulation & water cooling is not required. If I use it 2 minutes each time 6 to 8 times in 30 minutes 5 gallons of water gets hot quick. These can not be cooled with a fan.

Pretty sure those don't do much on a 2 volt power feed.

 

[tcmtech]

No, its for 100's of cycles...so a proper spec is required.

Well that info would have been useful earlier on.

 

[gary350]

Pretty sure those don't do much on a 2 volt power feed.

My digital VOM shows 9.0 ohms for a hot water heater element 1500W 120V = 12.5A

A 240V 3000W is 18.0 ohms

A 240V 4500w = math says 27 ohms

 

[Mosaic]

Well that makes gary's suggestion a failed one.

 

[gary350]

Well that makes gary's suggestion a failed one.

If you put 5 of the 1500W in parallel you get 1.8 ohms. Put more in parallel to get the ohm value you want. 9 in parallel = 1 ohm.

 

[ronsimpson]

Nichrome

I was looking at my wire collection.
I have some wire that is probably #6.
12 feet = 25mOhms.
I think if the wire is laying on the floor it will hold 80A. (as long as air can get to it) If the wire is not in free air the temp will clime too high.
A 12 foot role will heat and the inside conductors will burn. But if the role is in a metal bucket of water it should cool off the inter turns.
The hardware store has Cu or Al wire up to the size of my thumb. (house wire)
Look at wire size + current + temperature rise.
I was just thinking about what you can get from the store in your town.
If the battery is on the floor and you ran the wire from the battery to the sealing and back to the battery, might work. Or go with heaver wire and run up/down and up/down. If the wire only gets warm it is much safer than using wire that gets red hot.

 

[tcmtech]

If you put 5 of the 1500W in parallel you get 1.8 ohms. Put more in parallel to get the ohm value you want. 9 in parallel = 1 ohm.

Yes and he needs to pull about 80 amps at 2 volts so he would need about 360 of them.

The last time I replaced a water heater element it cost about $30 so to make his 2 volt 80 amp load bank using your concept it would cost him around $11,000 not including teh other material to connect everything together.

To be honest he could make your design out of 400 10 ohm 1/2 watt resistors and be about $10,950 ahead on the game.

Me thinks you are missing a huge and obvious number of details on what his is wanting to do.

 

[Mosaic]

I was looking at my wire collection.
I have some wire that is probably #6.
12 feet = 25mOhms.
I think if the wire is laying on the floor it will hold 80A. (as long as air can get to it) If the wire is not in free air the temp will clime too high.
A 12 foot role will heat and the inside conductors will burn. But if the role is in a metal bucket of water it should cool off the inter turns.
The hardware store has Cu or Al wire up to the size of my thumb. (house wire)
Look at wire size + current + temperature rise.
I was just thinking about what you can get from the store in your town.
If the battery is on the floor and you ran the wire from the battery to the sealing and back to the battery, might work. Or go with heaver wire and run up/down and up/down. If the wire only gets warm it is much safer than using wire that gets red hot.

Yes, my current load for 6 & 12V batteries uses #16 nichrome with an 80A relay switching at the midpoint of the nichrome for the 6V EMF. That load only demands about 20A peak which works out to a bit over 2' of the nichrome which is configured (kinda zig zag) almost directly onto a 120mm, 80cfm metal fan intake. It does glow dull red under max load, but holds up ok over the longer term. The load is throttled/averaged via a PWM controlled NFET (2.5mΩ) to produce a low loss electronic load that focuses the heat on the fan cooled nichrome.

I'm going to try a similar approach for the 2V load, but over 10% of the wattage is going into the NFET now and another 10% into connection losses. So I'll need to thermally profile everything with a wind tunnel type arrangement for management.
Too bad Peltier junctions need 12V to run as this could have been used to as a load and cool the switching transistors at the same time (Seebeck effect).

With the 12V/20A load the TO247 Transistor only sees 1W peak dissipation making a Peltier solution unnecessary.