# [EVDL] Maximum ADC Voltage?



## EVDL List (Jul 27, 2007)

> --- Ben Apollonio <[email protected]> wrote:
> 
> > What is the maximum safe voltage for an ADC
> > FB-4001A? I know they're
> ...


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## EVDL List (Jul 27, 2007)

> Jim Husted wrote:
> 
> > --- Ben Apollonio <[email protected]> wrote:
> >
> ...


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## EVDL List (Jul 27, 2007)

> James Massey wrote:
> 
> >Bear in mind that there is difference between pack voltage and the voltage
> >that the motor sees. The motor will always see less than full pack
> ...


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## EVDL List (Jul 27, 2007)

> James Massey wrote:
> 
> > So why didn't you say it that way, instead of saying it in a
> > way that can be interpreted as though the motor wouldn't see
> ...


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## EVDL List (Jul 27, 2007)

Roger & James,

I'm trying to understand what the motor really sees from the PWM
controller. I have a power panel for my RC planes. This panel runs off
of a 12v battery. I have a cord which I use to heat my glow plug for
starting the engine. The glow plugs are heated just fine with a single
1.2v NiCd and can be blown with too much more than that. I think that
3v is the limit. I have a dial on my power panel which adjusts the
on-off ratio of the power panel to the glow plug. The pulse rate is
low enough to be audible. Since the 12v momentary pulse doesn't burn
out the plug, probably because of the heat-up time to burn out,
wouldn't a motor also have a lower likelihood of flashing over with a
short burst rather than a longer one? Doesn't it take time for the
charges in the insulating material to line up before breakdown so if
the duration is short enough breakdown doesn't occur? The other thing,
isn't there a voltage ramp-up time in the motor so that if the pulse
is short enough that the voltage never raises above a point lower than
the pack's load voltage?

I'm not trying to make this more technical but I'm curious. Also, I
may put a higher voltage pack in my S10 conversion so I don't have to
go with buddy pairs or some other paralleling method.

-- 
David D. Nelson

http://evalbum.com/1328

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## EVDL List (Jul 27, 2007)

> David Nelson wrote:
> 
> > wouldn't a motor also have a lower likelihood of flashing over with a
> > short burst rather than a longer one?
> ...


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## EVDL List (Jul 27, 2007)

Hi David,

No - heating and Flashover voltage do have capacity in common
but the time differences are staggering:

For a material to heat up you consider its heat capacity and
this will typically be in the order of seconds, you can apply
a signal pulsing with a frequency that you can hear and the
time while the signal is on or off does not make a measurable
difference in temperature of the material, unless you are
considering very small amounts of material.
Inside power transistors the micrometer (and smaller)
structures can be heated fast enough to change its
characteristics during pulses. But a motor or a glow plug
are so many orders of magnitude larger that their thermal
mass is not jerked up and down by the pulses in the signal.

Now for the Flashover voltage: the capacitance of the
windings of a motor will cause a certain ramp-up of voltage,
not an immediate rise to max voltage, but the size of this
capacitance is so small that in only a fraction of the
pulse duration the voltage has ramped up to max and the
full battery pack voltage will be present at the motor.
The only thing that can reduce Flashover events (and this is
the reason that many DC controllers do not go to 100% on)
is that the voltage drops back to zero between pulses.
This can help to extinguish any beginning flashover, but if
the voltage is high enough it will flashover quickly enough
to give enough plasma to immediately ignite again on the
following pulse.

Hope this clarifies,

Cor van de Water
Systems Architect
Proxim Wireless Corporation http://www.proxim.com
Email: [email protected] Private: http://www.cvandewater.com
Skype: cor_van_de_water IM: [email protected]
Tel: +1 408 542 5225 VoIP: +31 20 3987567 FWD# 25925
Fax: +1 408 731 3675 eFAX: +31-87-784-1130
Second Life: www.secondlife.com/?u=3b42cb3f4ae249319edb487991c30acb

-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of David Nelson
Sent: Monday, May 26, 2008 5:53 PM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] Maximum ADC Voltage?

Roger & James,

I'm trying to understand what the motor really sees from the PWM controller. I have a power panel for my RC planes. This panel runs off of a 12v battery. I have a cord which I use to heat my glow plug for starting the engine. The glow plugs are heated just fine with a single 1.2v NiCd and can be blown with too much more than that. I think that 3v is the limit. I have a dial on my power panel which adjusts the on-off ratio of the power panel to the glow plug. The pulse rate is low enough to be audible. Since the 12v momentary pulse doesn't burn out the plug, probably because of the heat-up time to burn out, wouldn't a motor also have a lower likelihood of flashing over with a short burst rather than a longer one? Doesn't it take time for the charges in the insulating material to line up before breakdown so if the duration is short enough breakdown doesn't occur? The other thing, isn't there a voltage ramp-up time in the motor so that if the pulse is short enough that the volt!
age never raises above a point lower than the pack's load voltage?

I'm not trying to make this more technical but I'm curious. Also, I may put a higher voltage pack in my S10 conversion so I don't have to go with buddy pairs or some other paralleling method.

--
David D. Nelson

http://evalbum.com/1328

_______________________________________________
For subscription options, see
http://lists.sjsu.edu/mailman/listinfo/ev

_______________________________________________
For subscription options, see
http://lists.sjsu.edu/mailman/listinfo/ev


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## EVDL List (Jul 27, 2007)

> David Nelson wrote:
> 
> > I'm trying to understand what the motor really sees from the
> > PWM controller.
> ...


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## EVDL List (Jul 27, 2007)

> Roger Stockton <[email protected]> wrote:
> > The motor is inductive, so the voltage can change "instantly", it is the current that cannot.
> >
> > I don't know the breakdown mechanism of the motor insulation. I'm not sure that breakdown of the motor insulation due to the applied voltages is a common problem with our DC vehicles at this point. I think most failures are associated with commutator/brush failure and/or mechanical failure associated with excessive speed.
> ...


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## EVDL List (Jul 27, 2007)

> --- Morgan LaMoore <[email protected]> wrote:
> 
> > This forms a low-pass filter: most of the AC voltage
> > appears on the
> ...


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## EVDL List (Jul 27, 2007)

Thanks everyone for your responses! I've been away from email for a 
few days so I just now finished reading through them all. Glad to see 
that I sparked off a such a good discussion, it sounds like it's not 
something that's particularly well understood.

It sounds as if I won't be the first person to run an ADC 9" at 192V. 
That is good news, and I had already decided it was probably safe. It 
sounds from the discussion like 216 or 240 might be pushing it a 
little, although my concern is range rather than performance. I guess 
I'll just use my best judgement.

I do not have a Z1K, but rather a T-rex 1000. While I can't limit the 
motor voltage, I can limit the top speed, which is pretty much the 
same thing.

Thanks again!
-Ben

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