create resistive load for capacity testing

[hwse]

Can an 120v AC resistive heating element be used to create a predictable load to test the total battery capacity? I am just thinking out loud so this could be drivel or just plain ignorant.

If I have a 120v 500W resistive horse water tank heating element, could I connect it to my battery to create a load.
The power equation is P=Iv so
P/v = I.
500W / 13v = 38.5A.

If I connect this element to my 12v battery, will it pull about 38 amps?

 

[Ampster]

If I connect this element to my 12v battery, will it pull about 38 amps?

You would need to know the resistance in Ohms. The lower the resistance the more the current. I tried one a long time ago and it did not pull many Amps. Instead I put a lot of high wattage low Ohm resistors in parallel to handle the current when I was trying to bleed down a cell.

 

[robby]

Can an 120v AC resistive heating element be used to create a predictable load to test the total battery capacity? I am just thinking out loud so this could be drivel or just plain ignorant.

If I have a 120v 500W resistive horse water tank heating element, could I connect it to my battery to create a load.
The power equation is P=Iv so
P/v = I.
500W / 13v = 38.5A.

If I connect this element to my 12v battery, will it pull about 38 amps?

No that is a 28.8 Ohm restive load, it would draw only .41A on 12V.

To get any kind of significant load on 12V your going to need a resistor or restive element that is not a typical house hold item. Just to get 10Amps you need 1.2 Ohms

 

[Ampster]

Just to get 10Amps you need 1.2 Ohms

I had trouble finding high wattage resistors with only 1 Ohm so that is why I put them in parallel.

 

[robby]

I had trouble finding high wattage resistors with only 1 Ohm so that is why I put them in parallel.

Yes and the second problem is heat. Using resistors to disipate 20A or 240W for even a 100A battery doing a capacity test is going to be a huge undertaking.
He is not only going to need huge resistors in parallel but also some kind of Active cooling system.

It's much easier to just use the Inverter and put the right size load on it to draw 20 Amps and then monitor the battery cable with a volt meter and Amp meter.

 

[NVS]

I bought one of these. Works pretty good.

https://a.co/2hkNhed

 

[Don B. Cilly]

One could also grab a few old car/motorcycle headlamps at a junk yard :·)
Or old-style bulbs for classic cars/bikes, really quite cheap new.
-

 

[mnd]

It's much easier to just use the Inverter and put the right size load on it to draw 20 Amps and then monitor the battery cable with a volt meter and Amp meter.

Inverter and a brine tank.

 

[triplethreat]

I bought a 200W 12V heating element from Amazon and used it to discharge and do a load test on my EVE 302AH cells once I got them built into a battery. I ran the battery down to the low voltage cutoff that I set in the BMS (2.55V/cell or 10.2 volts/battery). It was pretty steady pulling about 18.5 to 18.6 amps and I kept a small fan blowing on the resistor while running. I ended up with just under 305AH according to the Victron shunt.

 

[hwse]

Yes and the second problem is heat. Using resistors to disipate 20A or 240W for even a 100A battery doing a capacity test is going to be a huge undertaking.
He is not only going to need huge resistors in parallel but also some kind of Active cooling system.

It's much easier to just use the Inverter and put the right size load on it to draw 20 Amps and then monitor the battery cable with a volt meter and Amp meter.

That was why I was hoping that the 500W tank heater would do the job. It is a submersible unit used to keep a water trough from freezing over in winter. 500W into a thousand gallons of water will not heat up very much.

 

[robby]

That was why I was hoping that the 500W tank heater would do the job. It is a submersible unit used to keep a water trough from freezing over in winter. 500W into a thousand gallons of water will not heat up very much.

You kind of through us all of track because you stated:

"If I have a 120v 500W restive hot water tank heating element, could I connect it to my battery to create a load."

I think we all assumed you wanted to directly connect a 120V heater element directly to the Battery.
A 500W heater element is going to draw about 40 Amps from the 12V battery attached to the Inverter. So yes it will work just fine.

 

[hwse]

You kind of through us all of track because you stated:

"If I have a 120v 500W restive hot water tank heating element, could I connect it to my battery to create a load."

I think we all assumed you wanted to directly connect a 120V heater element directly to the Battery.
A 500W heater element is going to draw about 40 Amps from the 12V battery attached to the Inverter. So yes it will work just fine.

Your first thought was what I was hoping would be possible. I do not yet have an inverter other than my little 400W modified sine wave and was hoping that i could connect the 120v AC heater directly to 12v but it doesn't look like that will work. I am trying to find something I have on hand to do some testing due to time constraints and budget.

 

[740GLE]

Also those animal water heaters have internal thermostats, they shut off when the water is above 40f or so. No need to have hot water for your animals.

Automotive head light bulbs are the best way to creat cheap load banks.

 

[Miles B]

Your first thought was what I was hoping would be possible. I do not yet have an inverter other than my little 400W modified sine wave and was hoping that i could connect the 120v AC heater directly to 12v but it doesn't look like that will work. I am trying to find something I have on hand to do some testing due to time constraints and budget.

350W at 12V

0.41 Ω 500 Watt 12 Volt Resistor Diversion Dump Load for Wind Generator & Solar Panel

0.41 Ω 500 WATT WIND GENERATOR & SOLAR RESISTOR DIVERSION DUMP LOAD 12V

www.hurricanewindpower.com

 

[robby]

Requires active cooling and still gets very hot.

 

[Don B. Cilly]

https://diysolarforum.com/threads/discharge-one-cell.41846/#post-529279

 

[Saintsfan84]

I'm about to build my first lifepo4 battery using 4 280ah cells with a 200a smart BMS. I was thinking of how a dump load is used to divert excess energy for a wind turbine and thought of using something similar to run a capacity test on the battery once it's built. I was thinking of using 5 100w 1.0 ohm resistors in parallel attached to an aluminum finned plate to help dissipate the heat, fan blowing across it of course, and measure the power consumption with a shunt type battery monitor. The number of resistors could be changed to create a faster or slower pull on the batteries. I figure that 5 should pull 60 amps which is pretty close to a .2C discharge rate, if my calculations are correct.