"RE: [M]: Battery Problems" in the Meade Astronomy Archive

Subject: RE: [M]: Battery Problems
From: Bill Boyd
Reply To: mapug@shore.net
Date: Wed Aug 01 07:27:29 2001

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I wouldn't be too concerned about "square wave" "sine wave" issues. Most DC
to AC convertors use transistors to switch the DC current into inductive
loads which result in pretty poor square waves that are relatively low in
harmonics. That being said, most any load such as a
transformer/rectifier/filter will integrate most of the remaining AC wave.
This means switching or sine wave convertors are satisfactory for our
application.

Bill Boyd

-----Original Message-----
Sent: Tuesday, July 31, 2001 5:03 PM
Subject: Re: [M]: Battery Problems

I have been thinking , a lowpass filter should pretty much change the
"modified square wave" back into something a lot more like a sine wave
by reducing the higher order harmonics found in the square wave ...
those harmonics are also what probably causes the most noise and
other related problems... .. I will mull that over a bit more ... not
sure what to do about varying load impedances but can design one and
then see what effect of varying load impedances on harmonic
suppression might be ( or Doc G probably already knows ) ..

In fact the Meade Ac supply is somewhat of a low pass filter .. the
main issue is probably what goes on with the transformer , how it
likes the harmonics and whether they get thru to the rectifier diodes
to increase the peak inverse voltage the diodes see., or what leaks
around the diodes and filter capacitor.

Rgds... Hank

-----Original Message-----
Date: Tuesday, July 31, 2001 3:40 PM
Subject: RE: [M]: Battery Problems

>Chris--
>
>Thanks for your reply. I think that I am willing to risk running my
DC
>components--laptop and telescope--off a modified square wave
inverter,
>rather than spend that much.
>
>As for the "750 amps" for the marine battery, my battery is rated
650, and
>it is a 75 amp-hour battery. Presumably, the 750 would be about 85
>amp-hours. However, I am learning (I make every mistake once) that
marine
>batteries rated in cranking amps are not really pure deep cycle
batteries,
>but, rather, are hybrids, so I don't expect this battery to last all
that
>long being totally run down in a night's imaging. Next time, I will
look
>harder for a pure deep cycle battery, and I will try to get one at
least 100
>amp-hours.
>
>--Mark
>
>> -----Original Message-----
Of
>> Chris Frye
>> Sent: Tuesday, July 31, 2001 2:01 PM
>> To: LX200 User's Group
>> Subject: [M]: RE: Battery Problems
>>
>>
>> Mark de Regt wrote:
>>
>> >Chris--
>>
>> >I also use a large marine deep cycle battery and a charger. I
could
>> not
>> >find a true sine wave inverter without spending hundreds of
dollars for
>> one;
>> >I use a modified square wave 350 watt inverter. If you spent a
>> reasonable
>> >amount (as opposed to an unreasonable amount) on yours, I would be
>> >interested where you got it.
>>
>> >- --Mark
>>
>> My reply:
>>
>> I can research this further, if you want, but I think I bought it
from
>> one of the
>> dozens of new and used electronic supply catalogs I receive every
month.
>>
>> I paid $525.00 for it. In my case I think that the price was a
sound
>> investment
>> to protect a $3,195.00 telescope (10" LX200 with only 1 eyepiece)
:). I
>> also use
>> the inverter in my home laboratory on circuits that contain
inductors.
>> These
>> circuits will haywire with anything other than a true sine wave.
>>
>> I hope this helped.
>>
>>
>>
>
>
>

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I wouldn't be too concerned about "square =
wave" "sine wave" issues. Most DC to AC convertors use =
transistors to switch the DC current into inductive loads which result =
in pretty poor square waves that are relatively low in harmonics. That =
being said, most any load such as a transformer/rectifier/filter will =
integrate most of the remaining AC wave. This means switching or sine =
wave convertors are satisfactory for our application.

Bill Boyd

 

-----Original Message-----
 From: HENRY PFIZENMAYER [<A =
.att.net</A>]
 Sent: Tuesday, July 31, 2001 5:03 PM
 Subject: Re: [M]: Battery Problems

 

I have been thinking , a lowpass filter should pretty =
much change the
 "modified square wave" back into something =
a lot more like a sine wave
 by reducing the higher order harmonics found in the =
square wave ...
 those harmonics are also what probably causes the =
most  noise and
 other related problems... .. I will mull that over a =
bit more ... not
 sure what to do about varying load impedances but =
can design one and
 then see what effect of varying load impedances on =
harmonic
 suppression might be ( or Doc G probably already =
knows ) ..


In fact the Meade  Ac supply is somewhat of a =
low pass filter .. the
 main issue is probably what goes on with the =
transformer , how it
 likes the harmonics and whether they get thru to the =
rectifier diodes
 to increase the peak inverse voltage the diodes =
see., or what leaks
 around the diodes and filter capacitor.


Rgds... Hank

 

-----Original Message-----
 Date: Tuesday, July 31, 2001 3:40 PM
 Subject: RE: [M]: Battery Problems

 

>Chris--
 >
 >Thanks for your reply.  I think that I am =
willing to risk running my
 DC
 >components--laptop and telescope--off a modified =
square wave
 inverter,
 >rather than spend that much.
 >
 >As for the "750 amps" for the marine =
battery, my battery is rated
 650, and
 >it is a 75 amp-hour battery.  Presumably, =
the 750 would be about 85
 >amp-hours.  However, I am learning (I make =
every mistake once) that
 marine
 >batteries rated in cranking amps are not really =
pure deep cycle
 batteries,
 >but, rather, are hybrids, so I don't expect this =
battery to last all
 that
 >long being totally run down in a night's =
imaging.  Next time, I will
 look
 >harder for a pure deep cycle battery, and I will =
try to get one at
 least 100
 >amp-hours.
 >
 >--Mark
 >
 >> -----Original Message-----
n Behalf
 Of
 >> Chris Frye
 >> Sent: Tuesday, July 31, 2001 2:01 PM
 >> To: LX200 User's Group
 >> Subject: [M]: RE: Battery Problems
 >>
 >>
 >> Mark de Regt wrote:
 >>
 >> >Chris--
 >>
 >> >I also use a large marine deep cycle =
battery and a charger.  I
 could
 >> not
 >> >find a true sine wave inverter without =
spending hundreds of
 dollars for
 >> one;
 >> >I use a modified square wave 350 watt =
inverter.  If you spent a
 >> reasonable
 >> >amount (as opposed to an unreasonable =
amount) on yours, I would be
 >> >interested where you got it.
 >>
 >> >- --Mark
 >>
 >> My reply:
 >>
 >> I can research this further, if you =
want,  but I think I bought it
 from
 >> one of the
 >> dozens of new and used electronic supply =
catalogs I receive every
 month.
 >>
 >> I paid $525.00 for it.  In my case I =
think that the price was a
 sound
 >> investment
 >> to protect a $3,195.00 telescope (10" =
LX200 with only 1 eyepiece)
 :).  I
 >> also use
 >> the inverter in my home laboratory on =
circuits that contain
 inductors.
 >> These
 >> circuits will haywire with anything other =
than a true sine wave.
 >>
 >> I hope this helped.
 >>
 >>
 >>
 >
 >
 >

 

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