Hi experts.
I am hoping someone can assist me with choosing the right part for my project.
I have a small (lithium) battery powered motor for my inflatable boat. Battery is built in...and small... The only way to extend usage is to recharge it while on water. Company doesn't have external batteries. So the two "official" options are to charge internal battery with an AC adapter or their solar controller.

I cooked a chain using Ryobi 40V 6AH lithium battery > DC 40V to 12V Step Down Converter going into their solar charger and then to the motor. It works / charges, however I want to take solar controller out of the equation and just use a single, premade unit between battery and motor. Something simple, efficient and reliable. Based on numbers, can somebody suggest a device that will do the trick?

Battery - Ryobi 40V 6Ah Lithium-Ion

Original Solar controller for motor:
Input: 10-23V 10A Max
Output: 29.4V 4A Max

Original motor AC power supply for motor:
Specs from AC power supply:
Max Output Power: 117.6 W
Output Voltage (DC): 29.4 V
Output Current: 4.0 A

Thank you!

 

What is the charging voltage for that motor??? without knowing that there is no way that we can even suggest a power supply..
BUT my choice would be to open the motor package and measure the battery voltage. Then add a switch to either use the internal battery OR use an external battery with a step down switcher supply. OR get another battery with the same voltage and use it to power the motor.
I did not see those specs when I first saw the thread.

 

MisterBill2,
The goal is to get very close to original motor charger specs (which I've mentioned):
Max Output Power: 117.6 W
Output Voltage (DC): 29.4 V
Output Current: 4.0 A

From Ryobi 40V lithium battery (OP4060).

To my understanding, I need what is called DC-DC buck converter. There are just so many... I need help of determining which would be better for my application. I want one cased (pre built), I assuming with built in heatsink?

 

MisterBill2,
The goal is to get very close to original motor charger specs (which I've mentioned):
Max Output Power: 117.6 W
Output Voltage (DC): 29.4 V
Output Current: 4.0 A

From Ryobi 40V lithium battery (OP4060).

To my understanding, I need what is called DC-DC buck converter. There are just so many... I need help of determining which would be better for my application. I want one cased (pre built), I assuming with built in heatsink?

Hi,

Get the one with the highest efficiency that meets the specs.

 

The greatest efficiency would still be to connect an external battery pack that was the correct voltage for the motor, or a bit less.
Certainly that will require more effort, but if you are planning on having that motor for quite a few years it makes sense, because original batteries do not last more than a few years, at best.

 

Thanks for replies.
"The greatest efficiency would still be to connect an external battery pack that was the correct voltage for the motor"
Efficiency is a factor, but not crucial. I have several Ryobi batteries, I do want to use them. With current chain, I am able to get roughly 25% of charge from a single 40v 6Ah Ryobi battery. Which is sufficient for my uses.

The point of this thread... I was looking for help choosing a specific part based on the numbers, as I have no clue what is considered good quality, brands, etc. From what I've seen there are units ranging from $10-$200. I am definitely not looking for the top of the line stuff, but don't want junk either.

To recap:
I cooked a chain using Ryobi 40V 6AH lithium battery > DC 40V to 12V Step Down Converter going into their solar charger and then to the motor. It works / charges, however I want to take solar controller out of the equation and just use a single, premade unit between battery and motor. Something simple, efficient and reliable. Based on numbers, can somebody suggest a device that will do the trick?

 

Thanks for replies.
"The greatest efficiency would still be to connect an external battery pack that was the correct voltage for the motor"
Efficiency is a factor, but not crucial. I have several Ryobi batteries, I do want to use them. With current chain, I am able to get roughly 25% of charge from a single 40v 6Ah Ryobi battery. Which is sufficient for my uses.

The point of this thread... I was looking for help choosing a specific part based on the numbers, as I have no clue what is considered good quality, brands, etc. From what I've seen there are units ranging from $10-$200. I am definitely not looking for the top of the line stuff, but don't want junk either.

To recap:
I cooked a chain using Ryobi 40V 6AH lithium battery > DC 40V to 12V Step Down Converter going into their solar charger and then to the motor. It works / charges, however I want to take solar controller out of the equation and just use a single, premade unit between battery and motor. Something simple, efficient and reliable. Based on numbers, can somebody suggest a device that will do the trick?

Hi,

Did you check on Amazon (or similar)?
I had found many buck (step down) converters a while back, and even boost converters. The power ratings vary, and of course you have to keep an eye on the other specs like max input voltage. I could look around if you like.

 

thanks. I've seen some too.
For example this:
https://www.amazon.com/gp/product/B085T73CSD

But seems it is flimsy and reviews suck.
-----------------------------------
I like the build on these. Enclosed, larger heat sink, inline fuse:
https://www.amazon.com/dp/B0FZKB7Z8B
But they seem to cap at 24v output. Could not find one ~40v > 30v.


The reason for me to ask here, I thought that people could suggest a specific brand/unit.
Something like this one:
https://www.amazon.com/dp/B0FZKB7Z8B

 

I see what you mean now.

Have you looked at this one:

WWZMDiB CC CV Buck Converter DC 6-40V to 1.2-35V 20A 300W Power Supply Step Down Module for Solar Energy, Photovoltaic Energy, Industrial Equipment

It is hard to say how 'good' these are because the ones I used were mostly up to maybe 4 amps, with more typical 2 amps outputs.
You could ask the seller, and makes sure you have that 30 day return window Amazon is known for.
Don't know if your input source goes over 40v though, you might have to trick it with some diodes or something.
Looks to be around $10 USD.

All of the converters I got from Amazon worked ok but I have not purchased one in over 2 years now.
It says "frequently returned" but that does not mean that it does not work well, it just means most likely the people who returned it thought it would do something that it can't do. For example, the power is limited to 300watts.
It looks like there are a lot of similar ones by different sellers without any bad notes.

There is another double unit:
ASIN: B09DV6MW4Q
There are some good and bad reviews.

 

I am NOT the switcher supply design expert. Because reliability is more important than low cost, I buy good switchers from good manufacturers.
Good Luck!!

 

Hi,
this is not a transformer-selection problem.

Your system is battery → battery charging, entirely DC. A transformer only applies to AC systems. What you actually need is a regulated DC-DC power supply that electrically behaves like the original AC adapter.


Based on the manufacturer specs, the motor’s internal battery expects:

• 29.4 V DC
• Up to 4.0 A
• ~120 W max

That means the clean solution is a high-power DC-DC buck converter:

• Input: ~36–42 V (your Ryobi 40V battery range)
• Output: 29.4 V regulated (CV)
• Current: ≥4 A
• Power rating: 150 W+ recommended (thermal margin)

This would directly replace both your step-down stage and the solar controller.
Do not connect the 40V battery directly to the motor.


I wrote a short technical article explaining the reasoning, parameters, and safety considerations in more detail here:
https://xjkadapter.com/how-to-choose-a-dc-power-adapter-for-lithium-battery-chargers/

Hope this helps.

 

Matt, thanks....
by now, I know that
This is what I am here for. To see if somebody could recommend a specific unit. Hopefully fully assembled (cased, with heat sink)
Similar to this:
https://www.amazon.com/dp/B0FZKB7Z8B

The closest so far (uncased) recommended was this one:
https://www.amazon.com/WWZMDiB-Converter-Adjustable-Regulator-Protection/dp/B0B825HRB9
But judging by reviews it is poor quality.

 

Matt, thanks....
by now, I know that
This is what I am here for. To see if somebody could recommend a specific unit. Hopefully fully assembled (cased, with heat sink)
Similar to this:
https://www.amazon.com/dp/B0FZKB7Z8B

The closest so far (uncased) recommended was this one:
https://www.amazon.com/WWZMDiB-Converter-Adjustable-Regulator-Protection/dp/B0B825HRB9
But judging by reviews it is poor quality.

Hi,

It's always a little bit of a gamble, but with these devices we have to factor in the less-informed user factor. A lot of people who buy this stuff don't really know how to use it and usually can't interpret specs very well at all.

A good example I ran into was with a 1/4 inch drill bit. You would not expect that to be defective right? Well you'd be right, but still it got a LOT of bad reviews because of early breakage. As the users used it to drill with their hand drill motors, the bits would break. Sounds bad right?
Yes, except for one little detail: it was a solid carbide drill bit.
What does that tell you?
Right off the bat it tells me "don't use in a hand drill". It's made for automatic drill machines like a CNC machine. The reason being that it can't be tilted on an angle once the hole starts to form or it can snap. Even dropping the bit can snap it. I dropped a couple smaller ones and they snapped into a couple pieces. That's because they are super hard and brittle. When used right, they can drill through almost anything, but the catch is the drill has to remain perfectly perpendicular to the surface throughout the entire process (for regular perpendicular holes).

The bit was exceptional and the price was good, but the reviews were bad.

As to the converter, that one does have bad reviews but there are others JUST LIKE IT that do not have bad reviews. Do the math
Look for the similar models then and maybe choose one of those instead. Just make sure they still offer the 30 day money back.

 

For drill bits, I would of tried hardware/home improvement forum

I was just hoping that perhaps at specialized forum, in specific subtopic, tech people will point me to specific trusted encased device(s) for my application... if they exist. Not just Amazon search.

 

For drill bits, I would of tried hardware/home improvement forum

I was just hoping that perhaps at specialized forum, in specific subtopic, tech people will point me to specific trusted encased device(s) for my application... if they exist. Not just Amazon search.

Hi,

Yes, I understand fully. We all would like some guarantee that something is definitely going to work before we buy it.
The only way to do that is to find a forum where somebody bought the item already and used it for a year. That might be hard to find, but it could still be misleading. Sometimes you just have to use trial and error.

I could probably look up the ones I had purchased in the past, but like I said they were all much lower power. Every one of them worked though as I tested each one, and with some purchases I got 5 at a time because they were being sold as a 5 pack. All 5 worked. A neighbor of mine also bought a lot of different converters like buck and boost and buck/boost, and they all worked.
The only probably that I know of is that the power rating may not be what it appears to be. If it says 3 watts it may only go up to 2 watts for continuous operation, for example.

There is one sure way to get what you want, and that is to build one yourself. This is not super hard to do but you have to have knowledge of soldering and all that stuff, and follow schematics and buy the right parts. There are a LOT of members here that can help you with that if you decide to go that route. You can ask as many questions as you need to, and since a lot of people here have built many of these things in the past they will be able to help you. An example I did a few years back was with the LM2576 IC chip. It's a buck IC chip that goes up to 3 amps. It's in the line of "Simple Switchers" that were made by National Semiconductor.