Good morning,
Looking for some advice from folks who are waaaayyyy smarter than I am. I have a Lift Mate 12v boat hoist motor that is designed to run off of a boat battery, the amps (according to lift mate) that it draws (presumably under load) is 13a. I am looking to run this off of a 20v Dewalt battery…I talked with lift mate and they say it should not be run on more that 12v which is fine, I can get a 20v-12v 15a step down inverter off of Amazon cheap…The motor under load needs to run for about 1.5 minutes to fully lift the boat out of the water…Anyone have any thoughts if this will work?
That’s kind of an odd thing to say since the boat battery voltage is probably 12v nominal which actually might be in the range of 10v (hopefully not) to even >16v (equalizing charge). (See Off Grid/RV Lead Acid Maintenance, Charging, and Failure Modes)
You need more information. Usually motors draw a lot more amps than their nameplate amperage/horsepower rating would imply for a small period of time when they first start. For something like a big battery this is usually not a problem, but for the components in a buck converter it is probably much more significant.
You might be able to get better data from the manufacturer, but I’d recommend measuring the peak current draw (and cumulative watt-hours) yourself with a clamp ammeter and a decent size lead-acid battery. This has the advantage that it measures the real-world conditions with the weight of your actual anchor (I assume that’s what’s being hoisted).
The DeWalt battery can almost certainly supply sufficient amps and total power, but the challenge will be finding high quality power conversion electronics that can take that kind of abuse.
Also don’t forget that you need to protect the DeWalt battery from over-discharge since the battery doesn’t do this for itself. Your system should stop if the DeWalt battery drops below 15v or so.
In terms of quality power conversion hardware, the Victron Orion-Tr Smart 24/12-20 might do what you want. (Unfortunately, you probably would need the “Smart” one in order to be able to customize the low voltage cutoff.)
I’m assuming we’re talking about the bigger 20v DeWalt batteries here. i.e. 6 Ah or higher.
Yes, I have a 6 and a couple 5’s. Do
You feel step step down module to 12v is needed? I
Thought running only 8 more Volta would only help spin the motor faster….Thank You!
Good point with the initial draw too, I will hook everything up with the bot battery first and check true draw under load to see what that is…
I’m not sure, but 20v is definitely outside the normal operating range for a 12v nominal system.
I believe the two main problems to worry about (assuming this is a simple brushed motor) are overheating and premature electrical insulation breakdown - for example of the varnish on the windings of the motor.
If it’s not a simple brushed motor, then you’d need to worry about the monotor controller electronics all being rated for the input voltage. Things like capacitors and mosfets won’t be happy if the input voltage is outside what the circuits were engineered for.
The DeWalt 20V Max packs are a 5S configuration - so ~20V fully charged, which is definitely more than I’d be comfortable putting into a system designed for a 12V battery. If it’s designed around an automotive system, it’s probably going to handle 14-15V tops, and if it’s designed for a standalone 12V battery, it shouldn’t ever see north of about 13V. It’s likely to run on 20V… at least until something fails.
I also wouldn’t expect a 15A Amazon Special buck converter to handle starting and running that motor. Startup surges are brutal on a lot of the motor designs - I measured one of our Power Wheels at something like 50A with both motors locked. You’ll want 40-50A capacity to handle the startup reliably.
However, you might just measure the running current, do some math, and put a dropping resistor with a big heatsink in series. Half an ohm seems about right - if you have 10-12A running, that’s 5-6V drop, getting you down into the 12V range, though you’ll have to work off the under load battery voltage, not the unloaded voltage. You’ll be dumping 50W in that resistor, though, which will take some serious heatsinking. That has the advantage of helping reduce the motor startup surge, too.
As far as low voltage cutoff goes, I honestly wouldn’t worry about it. “Don’t be stupid.” 10A @ 2 minutes is only 0.33Ah, so a full battery, even a small one, shouldn’t have any real trouble supplying the energy needed. Just don’t leave it connected and running indefinitely.
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If you draw too hard from the battery, you can kill the battery. It sounds like that this won’t be a problem.
If you give too many beans to the device, you can burn out the device; this is more likely to be an issue, depending on how it is designed.
If it’s a very simple “power goes to motor with a switch” design, you are just going to overrun the motor for a bit, probably could do that for quite awhile.
If it’s a complex computer controlled motor then you could fry the board and kill it instantly.
Obviously the company isn’t going to say anything (though you could see if they offer a 24v version anywhere). So it comes down to how much you’re willing to risk your motor/battery.
You could also get a car jump start tool and see if that works, or just get a small battery to charge using the Dewalts.
Update… so, I fabricated all of my brackets and got everything hooked up this weekend. I ran on the 12v boat battery and it went up and down however very slow, so I said he’ll with it, I wired in the Dewalt 20v battery and it worked awesome, went up and down all the way three times with no issues, everything stayed cool and the battery only went down one bar, I probably could have went up and down another 4 times with no issues…. I appreciate the feedback from everyone.
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Excellent, glad it works. Just make sure you let stuff cool - it’s going to be running it harder than it’s designed.
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