I need a battery to put out up to 18 amps for a few minutes and 14 amps continuously for the life of the battery.
Normally I'd go with a Li-po pack, but apparently those are off limits for fire hazard reasons. It's a university engineering project for an intro level class, so that's understandable. A drill battery would be the next best thing since a connector would be easy to design and they're comparatively cheap.
I know the 18650s alone can usually supply a higher amperage, but the BMS might prevent this. Would I be able to get one big 5 Ah Dewalt battery4 Ah Masione battery to do this or would it be best to get two smaller 2.5 or 3 Ah batteries and connect them in parallel? My intuition tells me the 5 Ah battery probably has a very similar current limit to the smaller ones since they're designed for the same tools.
I could probably go with a cheaper off brand but I don't want to risk getting cheese grade chinesium for a battery with such high power demand. Edit: but that may be my only option since I need craftsman charger compatibility.
It would be much more advantageous to go with the one big one since I wouldn't need to balance the charges before connecting them and the BMS may not be happy with being connected to another pack.
Your load is 18a peak and 14a continuous and your asking if a 5ah battery is going to work? Maybe for 15minutes...
I would be looking at a 600cca +marine/rv lead acid battery designed to handle deep discharge.
It needs to be light and only run for 3 minutes minimum, it needs to power an 8lb hovercraft. A 75 Wh battery will run it for at least 13 minutes and that's fine. These are absolute maximum conditions and it's likely it won't be driven that hard.
It would be pretty simple to get hold of a battery and test it or to ask the manufacturer. That's likely to be far more useful than asking a bunch of random people here about a very specific battery.
I think that you should be asking your questions to the university safety officer, rather than on an international amateur forum.
There may be specific requirements, either stipulated by the university itself or by local health and safety legislation, that you must comply with that people on this site are not going to be aware of.
Health and safety standards are not the same the world over, what is considered acceptable practice in one territory may be prohibited in another.
slipstick:
It would be pretty simple to get hold of a battery and test it or to ask the manufacturer. That's likely to be far more useful than asking a bunch of random people here about a very specific battery.
Steve
I'm sure at least one of a bunch of random people have used a drill battery before. I'm not looking for information on a specific battery, just information on batteries in general. I only included the specific battery for reference. I'd like to avoid spending a couple hundred dollars on multiple batteries for testing, it's only logical that I'd at least ask before committing to that.
JohnLincoln:
I think that you should be asking your questions to the university safety officer, rather than on an international amateur forum.
There may be specific requirements, either stipulated by the university itself or by local health and safety legislation, that you must comply with that people on this site are not going to be aware of.
Health and safety standards are not the same the world over, what is considered acceptable practice in one territory may be prohibited in another.
I've already had the go ahead. If I wanted to break the rules, I'd be using a hobby RC li-po pack that I know would work.
There are minimal safety issues here. All I'm looking for is information on how much current a common drill battery is capable of delivering. If the battery can't do that, it'll either trip overcurrent protection or just run at a lower power.
The reason I'm asking, besides not having the batteries on hand, is just to get some general information. I've searched the web for hours looking for this information and all I can find is brief articles explaining what amp hours are. The manufacturers also don't release this information in datasheets to the public. I'm asking the community amateurs specifically because I know there may be someone first hand experience with unconventional power tool battery usage out there.
I should've known I'd be interrogated for saying anything other than, "HoW muCh amP does drill baTterY do?"
I've never personally tried testing the limits of a drill battery because lipos are just so easy to use these days. But probably a good place to find people who may have messed with such things is somewhere like RCGroups. There are folks over there who are very knowledgeable about the outer limits of battery usage. Try Batteries and Chargers - RC Groups
Ryobi makes 4Ah, 6Ah and 9Ah versions of their 18v batteries.
A 2 pack of the 9Ah battery is $140 at Home Depot.
Your 18A would be a 2C discharge.
Using a less expensive 6Ah ($120 for a 2 pack) would be a 3C discharge.
The 4Ah is $100 for a 2 pack. 4.5C discharge.
I am sure that none of these would be beyond what the power tools will pull.
There is some loss if efficiency when pulling higher amps from a battery. But if you only need 3 minutes of run time, I think you would be in good shape even with the 4Ah battery.
Thingieverse even has 3D printable adapters for these packs so you can print up a decent mount for the battery that will clip it in place. You will have to put in your own contacts and wires but that is low on the MacGyver scale.
Hobby RC packs are designed for high rates of discharge , being discharged in around 3mind in racing quads - so don’t understand why that “breaks the rules” , rather than using something that has unknown characteristics outside of its design specifications’( designed for power tool)
Why not just buy a battery that has a specification that suits your needs ?
OP stated in the first post that hobby LiPo packs are ruled out of this project by the university.
If a power tool can run a battery down in 10 minutes or less, then the battery is already being subjected to that current draw. Running a hovercraft is simply another current draw.
I just saw the added requirement for Craftsman charger compatibility.
My previous Ryobi comments are still valid for C rating but less so for brand compatibility.
This is entirely speculation, but I would be surprised if the power tool battery pack doesn't have over current protection of some sort and that it probably would kick in if one were to run it for several minutes at 3x rated capacity.
As an aside, while I understand the difficulty of dealing with bureaucracy, it's not obvious that operating a supposedly safe technology well outside of it's specified operating range is inherently safer than operating a potentially hazardous technology within it's specified range.
Finally it doesn't seem unreasonable in an engineering curriculum to have to safely deal with potentially hazardous materials. My apologies for a bit of an unhelpful rant.
When I have seen potentially hazardous batteries used, they were in a box in a box, the boxes were vented away from people and to the outside air, current and voltage were measured and recorded thousands of times per second, a fireman was there with appropriate attire and fire extinguisher, a fire truck was nearby, the fire department was on notice, the number of personnel present was limited, procedures were rehearsed, etc. etc..
vaj4088:
When I have seen potentially hazardous batteries used, they were in a box in a box, the boxes were vented away from people and to the outside air, current and voltage were measured and recorded thousands of times per second, a fireman was there with appropriate attire and fire extinguisher, a fire truck was nearby, the fire department was on notice, the number of personnel present was limited, procedures were rehearsed, etc. etc..
They must have been some pretty hairy batteries! - what was the application?
MrMark:
Finally it doesn't seem unreasonable in an engineering curriculum to have to safely deal with potentially hazardous materials. My apologies in for a bit of an unhelpful rant.
No apologies necessary. This is exactly what I was thinking
I did a bit of research and found a teardown of a cheap chinese aftermarket battery and it appears don't have overcurrent protection but the name brands typically do. In any case, my power requirement has gone down to 13amps peak which I believe is in the power tool range.
I think its safe to say you shouldn't use thermal batteries.
Unfortunately I don't have any hard data to provide but I have two bits of information:
My small Milwaukee Li-ION drill and "saws-all" has been pushed pretty hard (being a small battery, 12V 16Whr) and not complained.
We've researched electric vehicle batteries. Our considered involvement was be in the area of cooling the batteries. It seems the batteries have an internal maximum temperature above which they start to self discharge causing more temperature and so on .... to failure.
Again no hard data, but I think a suitable size electric tool battery would be fine for you use. Assuming:
The device is always monitored by a human when it is running.
You are outside, or at least in a large area.
Don't keep your face near the device when running.
I would be careful to not allow the batteries to build up temperature either in the charge or discharge process.
I'm sure folks will think I am too cavalier about a "safety" issue but even the hoverboards failing were only a local fire, not a life threatening explosion.
So be careful, be sure you don't hurt yourself of others and go for it.
UPDATE:
Thought I had after making the above post. I though this might help you:
In my experience you will get the best information from a battery supplier tech support person. Not the ones that answer the tech support line but the ones who work with the sales Reps. They have the most experience with customers trying to do odd things with their parts and in my experience are most likely to give you a practical (as opposed to an "official") answer.
If you take the rated torque and rpm of the drill the battery is for, convert to SI units (Nm and rad/s),
multiply them, you have the mechanical power rating of the motor. The battery will be able to handle
at least this amount of power or its not suitable for the drill!
