How long will a 0.9ma nano motor unit last on a DCell?

[bigkim100]

How long will a 0.7 amp nano motor run on a DCell, under no load?
Thanks for any help

 

[Bluejets]

D cell type..??

 

[bertus]

Hello,

You are not clear.
The title says 0.9ma.
The post says 0.7 Amp.
What is correct?

Bertus

 

[crutschow]

A good alkaline D-cell has about 18,000 mAh of capacity, so you divide that by your motor's current (0.7mA or 0.9mA as the case may be) to get the maximum life of the battery (it would be around two years).

 

[bigkim100]

A good alkaline D-cell has about 18,000 mAh of capacity, so you divide that by your motor's current (0.7mA or 0.9mA as the case may be) to get the maximum life of the battery (it would be around two years).

Honestly, thats close enough for me.

 

[dave9]

It would be very difficult to estimate this without more info such as whether your motor draws 0.7mA or 0.9mA, at what voltage it does that, what the minimum RPM is that is deemed acceptable to determine a termination voltage, what the current is at the reducing voltage as the battery drains, whether the motor can even achieve that minimum acceptable RPM or stalls (then what type of motor and what is the point of a no-load spec, surely it would have a load?), and considering that at such a tiny load, a D cell with a nominal 18Ah rating, would probably exceed that as long as it's alkaline or a lithium primary rather than a rechargeable with a self discharge rate that becomes significant over weeks/months/years of use.

 

[Audioguru]

Since nobody uses D cells anymore then if you find one it might be an old one with very poor quality (Super Heavy Duty garbage carbon-zinc) at The Dollar Store or it might be a Name-Brand alkaline D cell with a little C cell inside.
Even a Name-Brand D cell might have been running down in a store for a few years.

 

[bigkim100]

This is the Motor....
https://www.ebay.ca/itm/12220193586...rentrq:740e8adf17b0acf22aad04aefff9f4c6|iid:1


Ok, lets just say a Duracell D-cell

 

[dave9]

It's been ages since I bought D-cells, but don't some of the major alkaline manufacturers put a date code on them like they do other sizes, so you're assured of how old they are? I want to say they rate for 10 years or something so subtract 10 from the best by date to know the manufacture date.

The linked motor is always under load due to the vibrating weight, and probably would wear itself out in months if not less due to the tiny sleeve bushing handling the stress of that, if not the brushes failing first, also considering no manufacturer brand is specified so unknown quality.

Consider the application it is designed for, momentary use not continuous duty where a small enough size to fit in a phone is more important than running hours lifespan, and it specs the minimum voltage as 1.5V so a single D cell is not necessarily suitable since it will be below 1.5V for the majority of its capacity... if it operated reliably below 1.5V, you'd think that they would specify that.

It could work fine for a while, but I'dwant to test rather than assume it, using a variable voltage supply to see how low it can go and keep spinning or if it will be stopped and started, how low before it can't spin up. I'd sooner use 2 x AA NiMH cells in series, but with the higher battery voltage and RPM, the motor would wear out that much faster.

 

[bigkim100]

I only want it turned on once for a few seconds every 30 minutes or so, is that possible, and still have this run a long time

 

[dave9]

Yes it's possible, but I can't predict the lifespan at any particular duty cycle without some data. It's dirt cheap so I might buy a few of them if this is important to keep running a long time, then there is still the issue of how low a voltage it can use, which you may have to determine experimentally unless you can find someone else using this specific motor and providing that data.

The surer solution for the voltage issue would be to start with a signficantly higher voltage battery, with enough voltage margin to use a buck regulator circuit to arrive at 1.5V. You'd suffer some efficiency loss but the buck regulators on ebay capable of far more than the spec'd 80mA @ 1.5V, are cheap and tiny.

 

[bertus]

Hello,

From the ebay page:

At 1.5 Volts the motor takes 80 mA.
At 3 Volts the motor takes 160 mA.

Where did you get the 0.9 ma ?

Bertus

 

[dave9]

^ Thanks, yeah I think I was half asleep when I wrote the below in a prior post.

It would be very difficult to estimate this without more info such as whether your motor draws 0.7mA or 0.9mA,

 

[Audioguru]

The specs for the motor says it draws 80mA from 1.5V. The specs say the motor runs when it gets 1.5V to 3V. Then maybe it stops in a week when the battery voltage drops to 1.4V?