[Healeys] current draw of wipers

m.g.sharp at sympatico.ca m.g.sharp at sympatico.ca
Sun Mar 14 10:49:24 MDT 2021


Thank Bob and Mike, that makes intuitive sense based on the term “stall
current”, but I am surprised that they would give  that as a specification,
which is why I though it might be something else.  Why would they provide a
stall current for wipers, but not the starter motor, which can also lock up?
Also, if  the stall current for the wiper cold is 14 A, then why not put a
10A fuse on the circuit to save the motor if something jams?

Mirek

-----Original Message-----
From: m.g.sharp at sympatico.ca <m.g.sharp at sympatico.ca> 
Sent: March 14, 2021 12:47 PM
To: 'Bob Haskell' <rchaskell at earthlink.net>; 'healeys at autox.team.net'
<healeys at autox.team.net>
Subject: RE: [Healeys] current draw of wipers

A sign of my advancing years and arcane brain is that I often forget to just
"google it".  The inter-web says:

"Stall current is the maximum current drawn, when the motor is applying its
maximum torque, either because it is being prevented from moving entirely or
because it can no longer accelerate given the load it is under."

Given that, I imagine that the draw will increase as resistance in the wiper
mechanism increases.  So old, stiff grease, general wear, bushings in the
wheel boxes creating friction, etc., will all increase the current draw.
Unless I actually find the energy and initiative to go out and measure it, I
think I'll use something like 5-6A in my calculations.

Still happy to hear opinions/experience on bulbs (halogen vs LED) for the
spot lamps.

Cheers, Mirek





-----Original Message-----
From: Bob Haskell <rchaskell at earthlink.net>
Sent: March 14, 2021 11:36 AM
To: m.g.sharp at sympatico.ca; healeys at autox.team.net
Subject: Re: [Healeys] current draw of wipers

Mirek,

I believe that stall current is the load developed when the motor is not
able to rotate - the mechanism is locked up - wipers frozen to the
windshield.  I"m an oldish mechanical engineer, not electrical.  So someone
else may have a better answer.

Cheers,

Bob Haskell
Austin Healey 3000 BN7/BT7 registrar

On 3/14/21 10:31 AM, m.g.sharp--- via Healeys wrote:
>
> Happy Sunday!,  I am making some decisions on bulbs (and the LED
> equivalent) for some Lucas Spot lamps I am fitting to my BT7, and I am 
> concerned about the total draw if I have headlamps, spot lamps and 
> wipers on.  I know it is getting close to the measly 22 amp max output 
> of the generator.
>
> The manual has specs for the wiper motor: “normal running: 2.3 to 3.1 
> amps”. Then is gives “Stall Current” for the motor hot as 8 amps and 
> for the cold motor 14 amps.  My question is, what is “Stall Current”?
> The draw is huge compared to the normal running draw.  Also, by cold 
> motor, I assume they mean the wiper motor as I cannot see how the 
> engine temp would matter. However, although I get it that electric 
> motors generate some heat, I don’t think of them as “warming up”, or 
> running hot or cold, so the huge difference between  “hot motor” and 
> “cold motor” stall current further confuses me.
>
> Any help from the electric whizzes out there would be appreciated.
>
> BTW – regarding bulbs for the Spots, I like the idea of using LEDs as 
> the current draw is so low and the light better, but I find that 
> bright piercing light inconsistent with the character of our cars (a 
> personal preference) and the price of them is almost 3 times a BPF 48 
> W quartz halogen bulb.  I also consider that I have been driving my
> BT7 for 46 years without spot lamps and got along OK, so I question 
> the need to go to LEDs, other than the advantage of low current draw.
> Any experiences from those of you who have spot lamps with 
> conventional bulbs and the older low output generator (i.e. BT/BN7 and 
> earlier), would be appreciated.
>
> Cheers, Mirek
>
>
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