Simple DIY Load Tester For 40 Volt Lithium Battery

Thread Starter

btvarner

Joined Jan 7, 2018
18
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!
 

LowQCab

Joined Nov 6, 2012
4,309
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.
.
.
.
 

AlanIdris

Joined Sep 3, 2023
2
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
 

dovo

Joined Dec 12, 2019
72
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.
 

dovo

Joined Dec 12, 2019
72
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.


1715987216605.png
 

Thread Starter

btvarner

Joined Jan 7, 2018
18
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?
 
Top