Recommendations for 20A, 250W load tester?

[jdege]

I've been playing with these:

MakerHawk Electronic Load Tester



The UI allows you to easily set current limits beyond what they can handle. And, of course, the provided cables are crap.

I was trying to use one, with 10GA cables with proper ring terminals, to discharge a 48V LiFePO4 battery, and it very quickly popped something and stopped working.

They're cheap enough, so I bought another, very conservatively configured it to cutoff at >150W and >3A, then adjusted it to draw about 2.7A, 140W.

At this draw it said it would require 30+ hours to drain the battery. I checked on it 24 hours later, and while I was looking it popped again, without my having touched it.

Are there load testing devices anyone can recommend that can manage higher currents and power levels?

This one says it'll handle 250W. Clearly it can't handle 150W.

I'd like something that could manage 20A at 12V and 5A at 48V. So that's pretty much the 250W this thing promises but doesn't deliver.

Ideas?

 

[robby]

The good ones are not cheap.
Will Prowse uses the CBA V Pro
West Mountain Radio
As you can see the price goes from a couple of hundred to a couple of thousand really quickly.
You could DIY yourself something using heating elements, running water and a coulomb meter.

 

[jdege]

The good ones are not cheap.
Will Prowse uses the CBA V Pro
West Mountain Radio
As you can see the price goes from a couple of hundred to a couple of thousand really quickly.
You could DIY yourself something using heating elements, running water and a coulomb meter.

It seems as if I want to draw more than 4A from my 48V battery, I'm looking at over $1,000.

Buying another sub-$100 piece of Chinese junk might be my best option.

Or wait until I get an inverter and plug in a space heater.

 

[robby]

It seems as if I want to draw more than 4A from my 48V battery, I'm looking at over $1,000.

Buying another sub-$100 piece of Chinese junk might be my best option.

Or wait until I get an inverter and plug in a space heater.

Or buy a cheap coulomb meter and create some load using cheap hotwater elements.
Each 3000W (19 Ohm) element should draw 2.6 Amp or 130W at 50Vdc.
Four of them in parallel would be roughly 4.7 ohms or roughly 10.6 Amps or 560W being drawn for a pack.
I see some Rheem 3000W elements for $7 a piece on Amazon.
Four of them installed into holes drilled in a Steel 55 Gallon drum with the top open and full of water should run for a bit time before the water gets too hot.
I had some fun with this cheap Energy meter which records power going in and out : Amazon

Total cost for 560W load should be under $150 including all parts except the wire.
Elements, Meter and 55 Gal Drum should be around $150
You could get a bit more fancy and add in a temperature sensor for the water and have it shut off the power before the water gets to hot. The meter will just resume counting once the water cools back down and the relay switches back on.
Only issue I see is that you need to be able to shutdown the load when the battery reaches 0% SOC.
Easy to manually do if your monitoring the battery display or coulomb meters Voltage. To automate it with a Relay to shut off the load when the voltage reaches X will add more money.

 

[jdege]

From what I can see, all these fancy electronic devices are so expensive because they do a bunch of stuff I really don't care about.

 

[robby]

From what I can see, all these fancy electronic devices are so expensive because they do a bunch of stuff I really don't care about.

If you are not seriously into solar as a business or building battery packs then it really is not worth it.

 

[DougfromdaUP]

Have you looked at incandescent light bulbs? 120 v lamps will dissipate about 1/4 of their rated wattage at 50 volt. They’re dirt cheap,will last forever and you can screw them in and out to switch them on and off.

 

[jdege]

Have you looked at incandescent light bulbs? 120 v lamps will dissipate about 1/4 of their rated wattage at 50 volt. They’re dirt cheap,will last forever and you can screw them in and out to switch them on and off.

That's a thought. Thanks.

 

[jdege]

As a follow-up - I found myself needing to drain four 12V 100Ah LiFePO4 batteries.

I headed down to the local home store, picked up a couple of clamp-on worklights, and two 120V 200W incandescent bulbs. Cut off the the Type A plugs and crimped on a few ring terminals, hooked them up to a pair of the 12V batteries, to see what would happen.

Clearly the internal resistance of the bulb isn't linear. Or maybe it's that it was DC instead of the AC.

By Ohm's Law, you'd expect that a bulb that would draw 200W at 120V would draw 20W at 12V. Which would be 1.7A.

Instead I got 0.5A. Which meant 100 hours to bring the SOC down to 50%.

So I went online to see who still carried 12V incandescent bulbs. Turns out West Marine still had some. Bulbs that would draw 50W are 12V.

Turns out they draw closer to 60W, and are pulling 5A. Ten hours to bring SOC down to 50%. Much more reasonable.

There's no way, though, that I'm going to connect these 12V 50W bulbs to my 48V batteries. Maybe the 120V 200W bulbs will work, there. That'll have to wait until these 12V batteries are off my bench.

 

[DougfromdaUP]

When I use ohm’s law I expect a resistance that dissipates 200 watts at 120v to use 2 watts at 12v.

Power = voltage squared divided by resistance

An incandescent lamp will do a little more at the lower voltage, because the resistance gets higher as the filament heats up, and the lower voltage won’t heat it to its normal operating temperature.

 

[jdege]

Sorry, right.

P = V × I​

So 200W at 120V means 1.67A.

V = I × R​

So 1.67A at 120V means 71.8Ω.

I = V ÷ R​

And 71.8Ω at 12V means 0.167A.

I'm seeing 0.5A, which would indicate that the resistance is lower at the lower temperature.

 

[JanisD]

First things first - resistance of incandescent lamp is far from linear, heavily increasing with temperature (up to 10 times).

If You need only a load, then for me the solution was 4 car headlight bulbs in series to check the solar panels with Vmp around 40 V. And in case of 55 W bulbs in reality it was close to 160 W. It's possible to use such loads in parallel to get the necessary load.
For 48 V system I will be more comfortable with 5 or 6 bulbs in one row (in case of freshly charged battery at 55-58 V).
For me it costed 0, as they were low/high beam bulbs with burned low beams waiting to be discarder .

If exact measurement is needed than some kind of coloumb counter (made one using ESP8266 controller, IN226 current sensor and current sensing resistor in series with bulbs) is Your friend.

 

[jdege]

I don't need any kind of measurements, what the battery's Bluetooth apps provide is sufficient.

For the 12V battery, the 12V 50W bulbs are sufficient. A single draws 5A, two in parallel draw 10A.

I found a 48V 80W forklift headlight that should probably work for the 48V batteries.

 

[HarryN]

When I need to discharge a battery pack, I just use an inverter ---- charger ---- charge a different battery pack.

The other option - we have a commercial pet blow dryer that pulls 18 amp @ 120 vac. It has 3 settings for power level, so a budget variable power load.

 

[jdege]

When I have my inverters set up that may be my approach.