Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Old October 10th 16, 02:25 PM posted to sci.electronics.repair
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A friend has a disabled buggy for short distance trips. It is supposed
to do 25 to 30 miles on fully charged batteries. Last week it stopped
dead after about 10 miles. It was retrieved by the insurance company
and taken to the workshop for repair. A fuse had blown and so both
batteries needed replacing. Can anyone explain how a fuse blowing
results in the batteries needing to be replaced. They are sealed lead
acid batteries.

Any ideas?

Steve

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Old October 10th 16, 02:55 PM posted to sci.electronics.repair
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On Mon, 10 Oct 2016 13:25:23 +0100, Stephen Wolstenholme
wrote:

A friend has a disabled buggy for short distance trips. It is supposed
to do 25 to 30 miles on fully charged batteries. Last week it stopped
dead after about 10 miles. It was retrieved by the insurance company
and taken to the workshop for repair. A fuse had blown and so both
batteries needed replacing. Can anyone explain how a fuse blowing
results in the batteries needing to be replaced. They are sealed lead
acid batteries.

Any ideas?

Steve


My guess is that it's the other way around. The bad batteries
(voltage lower than spec due to bad cells) caused the electronic
controller to draw too much current in an attempt to maintain speed.
That's just a guess, though. It is hard disagnose something with no
information. It is also possible they replace the batteries whenever
they do any other repair to avoid another trip to the shop as the
batetries reach end-of-life.

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Old October 10th 16, 03:18 PM posted to sci.electronics.repair
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On Mon, 10 Oct 2016 08:55:33 -0400, Pat wrote:

On Mon, 10 Oct 2016 13:25:23 +0100, Stephen Wolstenholme
wrote:

A friend has a disabled buggy for short distance trips. It is supposed
to do 25 to 30 miles on fully charged batteries. Last week it stopped
dead after about 10 miles. It was retrieved by the insurance company
and taken to the workshop for repair. A fuse had blown and so both
batteries needed replacing. Can anyone explain how a fuse blowing
results in the batteries needing to be replaced. They are sealed lead
acid batteries.

Any ideas?

Steve


My guess is that it's the other way around. The bad batteries
(voltage lower than spec due to bad cells) caused the electronic
controller to draw too much current in an attempt to maintain speed.
That's just a guess, though. It is hard disagnose something with no
information. It is also possible they replace the batteries whenever
they do any other repair to avoid another trip to the shop as the
batetries reach end-of-life.


The batteries were brand new about two months old!

Steve

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Neural Network Software for Windows http://www.npsnn.com

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Old October 10th 16, 03:21 PM posted to sci.electronics.repair
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On Mon, 10 Oct 2016 14:18:27 +0100, Stephen Wolstenholme
wrote:

On Mon, 10 Oct 2016 08:55:33 -0400, Pat wrote:

On Mon, 10 Oct 2016 13:25:23 +0100, Stephen Wolstenholme
wrote:

A friend has a disabled buggy for short distance trips. It is supposed
to do 25 to 30 miles on fully charged batteries. Last week it stopped
dead after about 10 miles. It was retrieved by the insurance company
and taken to the workshop for repair. A fuse had blown and so both
batteries needed replacing. Can anyone explain how a fuse blowing
results in the batteries needing to be replaced. They are sealed lead
acid batteries.

Any ideas?

Steve


My guess is that it's the other way around. The bad batteries
(voltage lower than spec due to bad cells) caused the electronic
controller to draw too much current in an attempt to maintain speed.
That's just a guess, though. It is hard disagnose something with no
information. It is also possible they replace the batteries whenever
they do any other repair to avoid another trip to the shop as the
batetries reach end-of-life.


The batteries were brand new about two months old!

Steve


I should have typed "two months ago!"

Steve

--
Neural Network Software for Windows http://www.npsnn.com

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Old October 10th 16, 03:26 PM posted to sci.electronics.repair
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Sealed Lead-Acid batteries Do Not like to be run dead. Ideally, they never should drop below 50% of capacity before being recharged.

Now, we get into hype and sales pitches. The "Advertised" range of these little go-buggies is how far they will go downhill, with a tailwind, carrying a 30 pound load after a full charge on a cool day. The actual safe range is about 1/2 of that, 2/3 once in a great while. Otherwise, the battery sulfates - and dies.

Fuses are not voltage-dependent devices, but current dependent. So, as the battery starts to drop, and the regulator pulls more and more current (at a lower voltage) to the motors, the motors will start to overheat. And eventually the fuse(s) will blow to prevent damage to the motors.

http://batteryuniversity.com/learn/a..._to_prevent_it

Peter Wieck
Melrose Park, PA



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Old October 10th 16, 04:16 PM posted to sci.electronics.repair
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On 10/10/2016 23:25, Stephen Wolstenholme wrote:
A friend has a disabled buggy for short distance trips. It is supposed
to do 25 to 30 miles on fully charged batteries. Last week it stopped
dead after about 10 miles. It was retrieved by the insurance company
and taken to the workshop for repair. A fuse had blown and so both
batteries needed replacing. Can anyone explain how a fuse blowing
results in the batteries needing to be replaced. They are sealed lead
acid batteries.

Any ideas?


Would the workshop receive more money if they decide that the batteries
need replacing, even if the batteries are ok? Changing the batteries
would be a quick and simple job involving very little labour or
knowledge, and the mark-up on the replacement batteries might be quite
large. That might be one explanation why the workshop decided to replace
them.

In fairness to the workshop, many people abuse batteries without mercy,
running them into deep discharge and then leaving them to sulfate, or
making them boiling hot with heavy currents for long durations.
Determining with certainty whether the batteries are just a bit flat or
have been damaged through abuse may be a very time-consuming job and
require much experience and knowledge, and if the batteries are found to
be good, then it would likely be unprofitable also. They may also be
uncertain about the condition of the batteries, and may fear that they
would make the customer unhappy if the batteries are bad and they don't
replace them.

The workshop may even think that performing an unnecessary battery
replacement is a way of doing the owner a favour, if an insurance
company is paying.

The fact that the batteries were able to blow the fuse is if anything a
sign that they might be in good health. A really knackered battery might
not be able to produce enough current to blow the fuse, depending on the
fuse rating.

If the owner is allowed to hang onto the old batteries then that would
be nice, but I expect the workshop wants to sell them for the scrap
value. In the event that the problem happens again with the new
batteries, that will show that it was some other problem.

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Old October 10th 16, 04:55 PM posted to sci.electronics.repair
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On Monday, October 10, 2016 at 9:55:49 AM UTC-4, Chris Jones wrote:

That could happen if the motor controller is very crude, but a good
motor controller would incorporate current limiting, and the current
limit should be set below the fuse blowing current.


Bluntly, I would be surprised if the motor controller is anything more than a primitive SCR speed control and a fuse as a last-resort. These go-buggies are just short of a racket, with a very few genuine exceptions. And a brush-type DC motor will pull current even when not turning right down to a dead-short when the voltage drops below what is necessary to turn the motor against the load - and THAT is what blows the fuse.

Peter Wieck
Melrose Park, PA
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Old October 10th 16, 05:21 PM posted to sci.electronics.repair
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On Monday, October 10, 2016 at 11:06:50 AM UTC-4, Phil Hobbs wrote:

Torque is proportional to current, no?

Yep. But a DC motor dead-stopped is a short circuit. And even a very nearly crapped-out battery may have enough to blow a fuse if dead-shorted. Fuse action is not voltage dependent (as long as the fuse is rated at a higher voltage than the application).

Peter Wieck
Melrose Park, PA


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