What is the approximate current drain of a typical stairlift running up and dow a flight of stairs?

Dale1700

Joined Mar 15, 2019
4
A used stairlift I purchased has two Genesis NP7-12FR 12volt, 7.0 AH.. batteries for operating the lift. These 2 batteries are connected in series to drive the lift's 24 volt motor. The Genesis Application Manual for the NP and NPX batteries shows the NP7 can actually produce 20 amps for about 6 minutes at 3 CA ( 21 amps?) before the terminal voltage decreases to 9 volts.

Can anyone give me an idea of what the battery amps drain would be when going up and down a set of stairs. I'm aware that the steepness of the stairs, the weight of a person, and other subtle factors are variables. But I'm just interested in a general range of the amperage drain unless more specific test data is available.

I've searched the Internet without success so far.

mvas

Joined Jun 19, 2017
538
What is the Model # of the used Stair Lift ?
If no model # , then what is the HP rating on the motor ?
Depends upon the gearing and the speed of the lift

An example: A 2/3 HP 24 V DC motor ..
No-Load = 3 amps
Full Load = 26 amps

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MisterBill2

Joined Jan 23, 2018
5,188
Do you need to know the current that the stair lift requires in order to know what power supply to get, or to figure how long the batteries will last, or for some other purpose? I have built a system that used those 7 AH batteries to provide 100 amps for almost a minute.
This forum includes a whole lot of folks with both a lot of knowledge and a huge amount of experience, and so with an adequate understanding of what an ultimate goal is they can usually provide very good advice. But without adequate information they can provide a whole world of guesses that may not apply at all.
For the stair lift application, if it is a good design the motor current should be about 3 amps. This is based on having 24 volts and 3 A being 75 watts, about 1/10 HP, a reasonable power for a motor lifting a person up a stairway at a modest speed. It is also based on being able to recharge every time it is at the bottom. So if it is less prudently designed the current may be closer to ten amps. There should be a fuse some place with should be rated a couple amps over full load, and that should be a clue, unless you are hoping to discover what size fuse to use.

wayneh

Joined Sep 9, 2010
16,242
Lifting a 300lb person up one story requires about 3,000 ft-lbs. There are 2,655,220 ft-lb per kWh, or 737.56 ft-lb per kWs. So lifting that person requires 4.07 kWs. Getting the job done in 8 seconds would require ~500W of shaft work. An electric motor and gearbox is 85-90% efficient, so you'd need about 600W at the receptacle or from a battery pack. That's less than 1HP and well below a standard home circuit (ie. 120VAC, 15A breaker). In fact you could cut the time in half and still handle it electrically, but I think there would be safety issues in going too fast.

Using a 12V battery, drawing 600W would require 50A for those 8 seconds. If you need to keep it under 20A, that's 240W and would take (a little more than 2X) longer to elevate the person. Might be OK. I was just guessing at the 8 seconds. If it takes 20 seconds, that might be fine. Seems a little slow to me but maybe not.

MisterBill2

Joined Jan 23, 2018
5,188
Lifting a 300lb person up one story requires about 3,000 ft-lbs. There are 2,655,220 ft-lb per kWh, or 737.56 ft-lb per kWs. So lifting that person requires 4.07 kWs. Getting the job done in 8 seconds would require ~500W of shaft work. An electric motor and gearbox is 85-90% efficient, so you'd need about 600W at the receptacle or from a battery pack. That's less than 1HP and well below a standard home circuit (ie. 120VAC, 15A breaker). In fact you could cut the time in half and still handle it electrically, but I think there would be safety issues in going too fast.

Using a 12V battery, drawing 600W would require 50A for those 8 seconds. If you need to keep it under 20A, that's 240W and would take (a little more than 2X) longer to elevate the person. Might be OK. I was just guessing at the 8 seconds. If it takes 20 seconds, that might be fine. Seems a little slow to me but maybe not.
Getting the lift done in 8 seconds would be a whole lot faster than those things go, and way too fast for an old person. There are all kinds of safety rules that require things to move much slower if they can't be certified idiot proof. 30 seconds is a much more reasonable time. Besides that, battery life does natter a bit and drawing 50A from a 7AH battery will not contribute to long life.

wayneh

Joined Sep 9, 2010
16,242
Getting the lift done in 8 seconds would be a whole lot faster than those things go, and way too fast for an old person. There are all kinds of safety rules that require things to move much slower if they can't be certified idiot proof. 30 seconds is a much more reasonable time.
Ah, OK, well that lowers the power demand quite a bit. Not the overall energy of course.

Dale1700

Joined Mar 15, 2019
4
Thanks for all the helpful information. It's greatly appreciated. I'll attempt to answer the questions that have been brought up in the responding posts. All contained interesting and informative info that I'm continuing to digest. They've refreshed some memories of my undergraduate days working on an EE degree. I'm retired and doing some experiments with the Genesis batteries and want to test them to see what capacity they will have after recharging. The suggestion to look at the fuse is something I should have thought about to get an idea of the max current the motor system was designed to handle. But I'd like to get some idea of the running current also.

The particular stairlift the batteries came from is an Acorn Superglide 120. The batteries are charged at the top and bottom of the rail/stairs with by a transformer. Only the batteries power the carriage/chair when going up and down the stairs. The carriage speed has an over speed shut off at about 27 ft/min as a safety feature. I haven't taken the carriage apart to get the info on the motor, and haven't been able to find that info in doing online searches. Seems pretty difficult to get detailed tech info ( egarts lists, schematic diagrams, diagrams of mechanisms assemblies to see how components fit together ) on stairlifts unless your a franchised dealer and/or factory trained technician.

I downloaded the 16 page Genesis Application Manual for the NP and NPX batteries with great technical info such as discharge current vs time, discharge time vs battery terminal voltage for various discharge rates, and many other charts. I'll be spending some time to digest a lot of that also.

Once again, thanks to all for your helpful inputs.

Alec_t

Joined Sep 17, 2013
10,906
This page shows various stairlift motors. Wattages are given (typically in the 200W-400W range).

MisterBill2

Joined Jan 23, 2018
5,188
This page shows various stairlift motors. Wattages are given (typically in the 200W-400W range).

OK, and so 360 watts would imply 15 amps. so the guess of 10 to 15 was reasonable for half the motors.
Still I ask what is the goal of gaining this information?
It is commonly understood that the rated amp-hours can be recovered running a battery at the AH/10 current level. This implies that running it at twice the AH current level the battery is not good for very many tripos up and down.
15 amps would also explain why there is not a system of brushes to power the drive motor, or a wired connection.

Dale1700

Joined Mar 15, 2019
4
OK, and so 360 watts would imply 15 amps. so the guess of 10 to 15 was reasonable for half the motors.
Still I ask what is the goal of gaining this information?
It is commonly understood that the rated amp-hours can be recovered running a battery at the AH/10 current level. This implies that running it at twice the AH current level the battery is not good for very many tripos up and down.
15 amps would also explain why there is not a system of brushes to power the drive motor, or a wired connection.
This page shows various stairlift motors. Wattages are given (typically in the 200W-400W range).

Dale1700

Joined Mar 15, 2019
4
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MisterBill2,
The best answer to why I'm spending time to get this kind of information: I recently had a new stairlift installed for my sister and became interested in all the mechanical and electrical components and how the system worked. In fact I bought another used one ( for about 1/10th the price ... nowadays about the price of an expensive technical book !) ) to learn how they are put together, perhaps take apart and have some spare parts if needed in the future. Having an EE background and 35 years in research and development, and having a life time interest in mechanical things and an avid do-it-youselfer, I've made a habit of getting as much technical information on things I've acquired or become interested in as I could. And I have a place for the used one ... after I've decided I've learned a much as I want Being retired and having time to research things I'm interested helps keeps me busy. Hope this answers your question. Maybe a bit long winded....but that happens with some of us old(er) folks.

Alex_t : Thanks Alex

MisterBill2

Joined Jan 23, 2018
5,188
[

MisterBill2,
The best answer to why I'm spending time to get this kind of information: I recently had a new stairlift installed for my sister and became interested in all the mechanical and electrical components and how the system worked. In fact I bought another used one ( for about 1/10th the price ... nowadays about the price of an expensive technical book !) ) to learn how they are put together, perhaps take apart and have some spare parts if needed in the future. Having an EE background and 35 years in research and development, and having a life time interest in mechanical things and an avid do-it-youselfer, I've made a habit of getting as much technical information on things I've acquired or become interested in as I could. And I have a place for the used one ... after I've decided I've learned a much as I want Being retired and having time to research things I'm interested helps keeps me busy. Hope this answers your question. Maybe a bit long winded....but that happens with some of us old(er) folks.

Alex_t : Thanks Alex
Ok Alex. Now that we understand it is in search of knowledge and not trying to fix some problem things make a bit more sense. We see a whole lot of questions with way too little information about the actual intended goal. So now that the goal is visible we can provide answers.