Looking to build a simple load tester for a 40V-4ah lithium Battery used in this case on the small electric lawn mower.

I have such a device for testing 12V, 5aH batteries used in stair lifts. It is simple. 2W, 4aH pre-LED car headlight bulb. Wires soldered to + and - on the bulb. Other ends attach to the battery poles. Light stays bright if the battery maintains load. Light quickly dims if the battery will not hold a load. Placing a volt meter on the poles at the same time provides how much voltage loss under load.

I am wishing to build a similar device for testing load on the above 40V battery. Can someone tell me the quickest method (& what size bulb to use) to do this? Not looking for something sophisticated. Just basic down & dirty tester. Thanks!

 

Go to your nearest Goodwill-Thrift-Store and buy all the Toasters that they have in the appliance section.
( I'm not kidding, this is exactly what I would do )

Radiant-Space-Heaters, ( the kind with no AC-Fan ), will work great too.
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Hi there 4 12V Car Globes in series will also work for more power put in parallel another bank. Not great but much cheaper than a proper load tester

 

Looking to build a simple load tester for a 40V-4ah lithium Battery used in this case on the small electric lawn mower.

I have such a device for testing 12V, 5aH batteries used in stair lifts. It is simple. 2W, 4aH pre-LED car headlight bulb. Wires soldered to + and - on the bulb. Other ends attach to the battery poles. Light stays bright if the battery maintains load. Light quickly dims if the battery will not hold a load. Placing a volt meter on the poles at the same time provides how much voltage loss under load.

I am wishing to build a similar device for testing load on the above 40V battery. Can someone tell me the quickest method (& what size bulb to use) to do this? Not looking for something sophisticated. Just basic down & dirty tester. Thanks!

For your 12V, 5 A-h (60 W-h) battery you are happy with a ~50W incandescent headlight. For your 40V, 4 A-h, 160 W-h battery using the same thinking three 12V, 50W headlamps in series works.

 

Yes that's fine to yours would be a bit cheaper

 

Yes that's fine to yours would be a bit cheaper

I missed your post because it came up while I was typing mine. Your 4 bulbs in series would work just as well and last longer. Ultimately we need 10 ohms, give our take some. I think LowQCab has the low cost solution with a used 120 VAC space heater set to 1500 watts. Resistance is 10 ohms.

The tempco of nichrome 80/20 is low enough that the 120VAC/1500W heater draws 170W/40V.

 

So, the 1500W space heater would draw the needed load? Are was talking as simple as connecting the heater plug to positive and negative posts & measuring that draw down with the multimeter?