# What buck converter input & output should I use?

#### Philip7445

Joined May 25, 2021
4
I am building a mobile watering/fertilizing tank for my wife. It is a 15 gallon plastic tank and I want to use one of my Ryobi 40v 6aH rechargeable batteries as the power source. My submersible pump is 12v 1.2a max and I am trying to figure out what specifications my buck converter should be to meet my needs. I am looking at a sealed buck converter with input range of 8v - 40v and an output of 12v 6a but is the 6a output too high? I cannot find an off the shelf buck that is sealed with an output of 12v 1.2a. I can find one with input of 8v - 40v and output of 12v 3a...would that be better?

#### DickCappels

Joined Aug 21, 2008
10,236
I cannot find an off the shelf buck that is sealed with an output of 12v 1.2a. I can find one with input of 8v - 40v and output of 12v 3a...would that be better?
It sounds better than no solution at all. Or do I misunderstand your question?

#### Ya’akov

Joined Jan 27, 2019
9,248
I am building a mobile watering/fertilizing tank for my wife. It is a 15 gallon plastic tank and I want to use one of my Ryobi 40v 6aH rechargeable batteries as the power source. My submersible pump is 12v 1.2a max and I am trying to figure out what specifications my buck converter should be to meet my needs. I am looking at a sealed buck converter with input range of 8v - 40v and an output of 12v 6a but is the 6a output too high? I cannot find an off the shelf buck that is sealed with an output of 12v 1.2a. I can find one with input of 8v - 40v and output of 12v 3a...would that be better?
The fact that it potentially provides more current than you need is not a bad thing. Remember, the rated supply current is a limit unlike the voltage which is a fixed thing. When you apply the rated voltage to the load it will draw as much current as it needs up to the rated current. If you needed 1.2A and the converter could only provide 500mA, that would be bad but being able to provide 3A is not bad.

The only tradeoff is cost, but availability trumps that here.

#### Philip7445

Joined May 25, 2021
4
Thanks for the rapid reply...well I had already purchased the 12v 6a buck....I hooked it up and it ran for all of about a 1 second, then a small pop was heard and now I have no output from the converter...UGH! Do I go and purchase a high amp buck or the lower amp buck?

#### Philip7445

Joined May 25, 2021
4
My other thought was maybe the listed draw of the pump was a typo? let me do some more research on that end.

Ok, after some research, all other similarly sized pumps are either 1.2a or 2.2a so I am fairly confident of that.
Here is what I purchased
PUMP

#### Ya’akov

Joined Jan 27, 2019
9,248
My other thought was maybe the listed draw of the pump was a typo? let me do some more research on that end.

Ok, after some research, all other similarly sized pumps are either 1.2a or 2.2a so I am fairly confident of that.
Here is what I purchased
PUMP
A lower current demand cannot damage something able to provide more current.

I would get a 12V battery and measure the actual current required by the pump at start and while running in water. To do that you will need a DMM that can do at least 10A current, and you need to make sure you know how to hook it up and use it.

#### Philip7445

Joined May 25, 2021
4
DMM = Digital Multi-Meter I assume...yeah, don't have one of those...nor do I know how to use one for more than testing Ohms, and voltage. ugh. I do have a 12v mobile phone external battery...I think it is rated for 2amp or so maybe 2.4a...I will give that a try.

#### Ya’akov

Joined Jan 27, 2019
9,248
DMM = Digital Multi-Meter I assume...yeah, don't have one of those...nor do I know how to use one for more than testing Ohms, and voltage. ugh. I do have a 12v mobile phone external battery...I think it is rated for 2amp or so maybe 2.4a...I will give that a try.
The problem is, you need to know how much current the pump is actually trying to draw. It might ruin at 1.2A unloaded but stall current (which is how it starts) and loaded down, it could be exceeding the 6A of the converter.

Maybe you should pick up a modestly priced clamp meter like this one. I have one of these and can recommend it highly. That would allow you to easily and safely check the current without inserting the meter in the circuit, and have other utility.