Hi everyone,
I've been surfing the web trying to find a schematic for a constant current DC load tester for use with a battery bank (48VDC) Ideally something that can handle 50amps or more would be fantastic! So far I've only found either low current or useless schematics online with nothing really suitable.
TIA for any help
Welcome to ETO!
Ouch! 50A or more @ 48V is gonna be expensive. A 1Ω load resistor, for example, is ~£75. What is your budget?
How accurate does the 'constant' current need to be?
Do you want a fixed 50A (or whatever) or must it be adjustable?
If adjustable, over what range?
I'm not surprised you haven't found a suitable circuit, but I'm sure the guys here could design something for you.
Hi EF,
Nice that you have joined ETO. I see you are from New Zealand; care to put it next to 'Location' on your user page so that it shows in the window next to your posts.
This helps us to know your component access and your mains voltage. It is also just plain interesting to know where people are.
I have done a few battery discharge circuits along the way, but not on such a grand scale; as Alec says, 'ouch'.
Basically you have these practical options, as I see it:
(1)
Fixed Load
(1.1) 1 Ohm 2.5KW resistor:
https://www.mouser.co.uk/ProductDetail/TE-Connectivity/TE2500B1R0J/?qs=iJVBkmKXgrlgth4ME9/cMw==
(1.2) 25 off 100W resistors in parallel (100W seems to be the maximum power before resistor prices rise disproportionately).
(1.3) Connect an inverter to the battery and connect the inverter mains output to a 2.5Kw (approx) load: domestic heater, kettle element, oven element, oven cooking ring. This approach could be converted into variable constant current (if that makes sense) by adjusting the inverter output voltage.
(2)
Variable load switched steps
(2.1) Say, 25 off 100W resistors that could be switched in or out to change the battery load.
(3)
Continuously variable
(2.1) Variable resistor. This is the simplest variable approach but would be costly
(2.2) 48V input 2.5KW switch mode power supply, with output voltage adjustable from 0V upwards, connected to a 2.5KW load. This could be modified to generate a variable constant current load.
(2.3) Custom variable electronic. This could be designed to draw an adjustable constant current. The circuit would use basic electronic techniques and would be simple to design. But it would involve a lot of circuitry, mainly repetition, and large heat sinks. I hope you choose this approach because, not only will it give the best performance, but it will be the most fun.
One thing to bear in mind, whichever approach you choose, is that the load would be dissipating 2,500 W (powerful domestic heater) and that heat would need to be conducted away from the electronic components and also out of the room that the equipment is located in. As a result, the load is liable to be quite physically large. Even with the simple single fixed-load resistor you would be wise to provide fan cooling to get the heat away from the resistor.
I do hope that you get back and tell us which approach you favor.
spec