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nuckolls.bob(at)aeroelect
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 Posted: Wed May 19, 2010 11:26 am Post subject: 24 volt and 12 volt Sharing Common Ground? |
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At 02:00 PM 5/19/2010, you wrote:
<pinetownd(at)volcano.net>
This isn't an airplane application, but the answer may also be
helpful for people with mixed 24 volt and 12 volt systems on their airplanes.
I'm building a generator to help charge a large (2,500 pounds)
stationary 24 volt battery pack. I have a small, single cylinder,
air cooled, diesel engine that will drive a 24 volt truck alternator
via "V" belt and pulleys.
The diesel engine has a 12 volt starting battery, 12 volt starter,
and a 12 volt alternator. It is negative ground, through the crankcase.
<snip>
Is it okay for them to share a common ground?
Absolutely . . .
The large battery pack, the large diesel generator, and my 120/240
volt AC house circuits are all grounded to the earth (as in planet
earth) in compliance with US electrical codes. It seems like the 24
volt and 12 volt systems sharing a common ground should be okay,
since everything else is happy to share connection with the earth,
but some 24 volt alternators are supplied with an insulated ground
terminal so that the case is not grounded. That makes it seem like
sharing a common ground might be a problem.
Note: This may not be an ideal use of either the engine or the
alternator, but my main purpose is the fun of learning something new
and if I happen to get something useful out of it, that's even better!
Double note: The large battery pack is normally charged by solar
photovoltaic panels with a large diesel generator for backup. This
new generator system I'm building will not be the primary charging
source; it's a backup to the backup.
Your "earth ground" analogy is a good one. "Ground"
simply implies a common reference. There ARE specialized
instances where one MIGHT want to operate an
alternator (-) terminal at something other than
common ground . . .
A few years ago, one of my builders wanted to have
a 14/28v aircraft with robust support of two
batteries in series. In this case, one 14v alternator
was operated in the conventional configuration. The
second alternator/battery combination was stacked
on top of the first. Thus the "top" alternator's
(-) connections needed to be isolated.
Haven't heard from this guy in many years. I don't
know if his project was ever finished.
Bob . . .
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Dennis Johnson
Joined: 10 Jan 2006
Posts: 89
Location: N. Calif.
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| Posted: Wed May 19, 2010 12:13 pm Post subject: Re: 24 volt and 12 volt Sharing Common Ground? |
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Hi Bob,
Thanks for the speedy reply! I've got the wire feed welder ready to go and I'll finish welding the frame together. Not having to isolate the ground on the 24 volt truck alternator will make things a little easier.
Thanks,
Dennis
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