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Battery Contactor Voltage Drop

 
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paul(at)eckenroth.com
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PostPosted: Sun Apr 07, 2019 11:18 am    Post subject: Battery Contactor Voltage Drop Reply with quote

What is the typical voltage drop across the poles of a healthy battery contactor.  Is there a failure or aging mode where the voltage drop increases.  How about typical voltage drop across the diode bridge rectifier for the essential buss.  After eleven trouble free years I need to sort out some problems with my RV9A.  Thanks for any information.

Paul


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PostPosted: Sun Apr 07, 2019 1:31 pm    Post subject: Battery Contactor Voltage Drop Reply with quote

On 4/7/2019 2:16 PM, Paul Eckenroth wrote:
Quote:
What is the typical voltage drop across the poles of a healthy battery
contactor. Is there a failure or aging mode where the voltage drop
increases. How about typical voltage drop across the diode bridge
rectifier for the essential buss. After eleven trouble free years I
need to sort out some problems with my RV9A. Thanks for any information.

Paul
Drop across a good contactor should be hard to measure reliably with a

regular voltmeter.

Drop across a typical silicon diode will be zero with no load, but will
be around 0.7V at any significant load.
If you have a Schottky diode (not likely, but possible), it will be
around 0.5V or less under load.

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N509RV(at)eckenroth.com
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PostPosted: Mon Apr 08, 2019 7:33 am    Post subject: Battery Contactor Voltage Drop Reply with quote

Thanks for the information Charlie.  The reason for the question is that I have 1 EFIS each on the regular buss and the E buss which show .9V difference.  Does the diode degrade in a way that would increase voltage drop.

Paul


On Sun, Apr 7, 2019 at 5:34 PM Charlie England <ceengland7(at)gmail.com (ceengland7(at)gmail.com)> wrote:

Quote:
--> AeroElectric-List message posted by: Charlie England <ceengland7(at)gmail.com (ceengland7(at)gmail.com)>

On 4/7/2019 2:16 PM, Paul Eckenroth wrote:
> What is the typical voltage drop across the poles of a healthy battery
> contactor.  Is there a failure or aging mode where the voltage drop
> increases.  How about typical voltage drop across the diode bridge
> rectifier for the essential buss.  After eleven trouble free years I
> need to sort out some problems with my RV9A.  Thanks for any information.
>
> Paul
Drop across a good contactor should be hard to measure reliably with a
regular voltmeter.

Drop across a typical silicon diode will be zero with no load, but will
be around 0.7V at any significant load.
If you have a Schottky diode (not likely, but possible), it will be
around 0.5V or less under load.

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PostPosted: Mon Apr 08, 2019 8:03 am    Post subject: Re: Battery Contactor Voltage Drop Reply with quote

Paul,
The diode is fine. A voltage drop of 0.9 volts across a diode is normal. The voltage drop depends
on the diode characteristics and the current. Some power diodes will drop 1.5 volts or more.


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PostPosted: Mon Apr 08, 2019 9:30 am    Post subject: Battery Contactor Voltage Drop Reply with quote

As long as the operating voltage with the alternator running is 'normal' (around 14V), I wouldn't be concerned about a 0.9V drop from primary bus across a standard diode block. If the diode is a typical 'full wave rectifier' (square metal or plastic block with 4 leads), and the source is feeding the '-' terminal and the load is on the '+' terminal, the voltage drop will be higher since the path is actually through two diodes in series. Not a big deal as long as you understand what's happening. Only time it might matter is after alternator loss, at the very end of battery life, *if* the E bus is still fed through the diode.

Charlie

On 4/8/2019 10:31 AM, Paul Eckenroth wrote:

Quote:
Thanks for the information Charlie.  The reason for the question is that I have 1 EFIS each on the regular buss and the E buss which show .9V difference.  Does the diode degrade in a way that would increase voltage drop.

Paul




On Sun, Apr 7, 2019 at 5:34 PM Charlie England <ceengland7(at)gmail.com (ceengland7(at)gmail.com)> wrote:

Quote:
--> AeroElectric-List message posted by: Charlie England <ceengland7(at)gmail.com (ceengland7(at)gmail.com)>

On 4/7/2019 2:16 PM, Paul Eckenroth wrote:
> What is the typical voltage drop across the poles of a healthy battery
> contactor.  Is there a failure or aging mode where the voltage drop
> increases.  How about typical voltage drop across the diode bridge
> rectifier for the essential buss.  After eleven trouble free years I
> need to sort out some problems with my RV9A.  Thanks for any information.
>
> Paul
Drop across a good contactor should be hard to measure reliably with a
regular voltmeter.

Drop across a typical silicon diode will be zero with no load, but will
be around 0.7V at any significant load.
If you have a Schottky diode (not likely, but possible), it will be
around 0.5V or less under load.

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PostPosted: Mon Apr 08, 2019 2:48 pm    Post subject: Battery Contactor Voltage Drop Reply with quote

Quote:
If the diode is a typical 'full wave rectifier' (square metal or plastic block with 4 leads), and the source is feeding the '-' terminal and the load is on the '+' terminal, the voltage drop will be higher since the path is actually through two diodes in series.

All of my drawings show power input
on an AC terminal (~) and output
on the (+). This uses only one of
the four diodes to minimize voltage
drop.

Quote:
Not a big deal as long as you understand what's happening. Only time it might matter is after alternator loss, at the very end of battery life, *if* the E bus is still fed through the diode.

Correct. Your radios are 'speced' to function
to 10V or less. By the time a battery gets
down to 10v (lead acid) or 11.2v (LiFePO4)
the battery is 'used up'. This is why the
e-bus alternate feed switch is closed any
time the alternator is off line . . . which
lets the electro-whizzies suck the battery
dry.

Any time the alternator is working, voltage
drop in the normal feed diode is insignificant.


Bob . . .


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PostPosted: Mon Apr 08, 2019 4:30 pm    Post subject: Battery Contactor Voltage Drop Reply with quote

I appreciate everyone's comments.  I thought I had a problem which has now evaporated.

Paul
On Mon, Apr 8, 2019 at 6:52 PM Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:

Quote:
Quote:
If the diode is a typical 'full wave rectifier' (square metal or plastic block with 4 leads), and the source is feeding the '-' terminal and the load is on the '+' terminal, the voltage drop will be higher since the path is actually through two diodes in series.

  All of my drawings show power input
  on an AC terminal (~) and output
  on the (+). This uses only one of
  the four diodes to minimize voltage
  drop.

Quote:
 Not a big deal as long as you understand what's happening. Only time it might matter is after alternator loss, at the very end of battery life, *if* the E bus is still fed through the diode.

  Correct. Your radios are 'speced' to function
  to 10V or less. By the time a battery gets
  down to 10v (lead acid) or 11.2v (LiFePO4)
  the battery is 'used up'. This is why the
  e-bus alternate feed switch is closed any
  time the alternator is off line . . . which
  lets the electro-whizzies suck the battery
  dry.

  Any time the alternator is working, voltage
  drop in the normal feed diode is insignificant.


  Bob . . .


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