Previous in Forum: Type Test Report of Battery   Next in Forum: DC Chopper
Close
Close
Close
44 comments
Rate Comments: Nested
Participant

Join Date: Dec 2010
Posts: 3

DC Battery Fault

12/10/2010 6:16 AM

I have a bank of dc battery cells with a negative to earth voltage of 17V The bank is totally disconnected from any earthed parts, can any one explain this ?

Register to Reply
Pathfinder Tags: Dc Battery Faults
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Good Answers:

These comments received enough positive votes to make them "good answers".

"Almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, vote them!
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on.
Posts: 32175
Good Answers: 839
#1

Re: Dc battery fault

12/10/2010 6:21 AM

What happens when a 24V filament lamp is connected, rather than a high-impedance DVM?

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply
Guru
United Kingdom - Member - Not a New Member Hobbies - Musician - New Member Hobbies - Fishing - New Member

Join Date: May 2006
Location: Reading, Berkshire, UK. Going under cover.
Posts: 9684
Good Answers: 468
#2

Re: Dc battery fault

12/10/2010 6:48 AM

What voltage were you expecting?

__________________
"Love justice, you who rule the world" - Dante Alighieri
Register to Reply
Participant

Join Date: Dec 2010
Posts: 3
#3
In reply to #2

Re: Dc battery fault

12/10/2010 6:53 AM

Iwas expecting 0 volts as cells were not connected to any external metal parts battery bank output voltage between positive and negative was24V

Register to Reply
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on.
Posts: 32175
Good Answers: 839
#4
In reply to #3

Re: Dc battery fault

12/10/2010 7:07 AM

What happens when a 24V filament lamp is connected between battery and earth, rather than a high-impedance DVM?

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on.
Posts: 32175
Good Answers: 839
#14
In reply to #3

Re: Dc battery fault

12/10/2010 9:46 AM

What is the ohms reading between the -ve terminal and earth?

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply
Guru
Hobbies - Fishing - New Member

Join Date: Jun 2008
Location: Raleigh, NC USA
Posts: 13529
Good Answers: 468
#17
In reply to #14

Re: Dc battery fault

12/10/2010 10:54 AM

I'm sorry.......did you say something? I hate it when they won't listen.

__________________
Those who would give up essential Liberty, to purchase a little temporary Safety, deserve neither Liberty nor Safety. Ben Franklin
Register to Reply
Power-User
India - Member - New Member

Join Date: Jul 2010
Location: India
Posts: 162
#5

Re: DC Battery Fault

12/10/2010 7:33 AM

Due to leakage from battery back to earth.

Check the cell corresponding to 17V w.r.t. -ve terminal of bank.

It may be giving trouble.

I also faced similar problem of leakage voltage which varies with change in humidity. The leakage tend to increase with high level of humidity in atmosphere.

__________________
When was last time you did something for first time.
Register to Reply Score 1 for Good Answer
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on.
Posts: 32175
Good Answers: 839
#6
In reply to #5

Re: DC Battery Fault

12/10/2010 7:50 AM

If the above-mentioned 24V filament lamp between the battery and earth won't light, then the problem is insignificant, and the OP has nothing to worry about.

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply Score 1 for Good Answer
Guru

Join Date: Oct 2010
Posts: 1294
Good Answers: 35
#8
In reply to #6

Re: DC Battery Fault

12/10/2010 9:13 AM

Going back to the OP: not connected to earth, perhaps, but what is the battery sitting on, and where are you connecting your voltmeter to earth?

Re: "the problem is insignificant"

While the problem is probably insignificant, it does represent a leakage path. When I used to maintain lead acid batteries, a leakage path like that usually indicated a need to clean the batteries, specifically around the terminals.

If that doesn't stop the leakage, there may be an actual acid leak from a cell.

Register to Reply
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on.
Posts: 32175
Good Answers: 839
#12
In reply to #8

Re: DC Battery Fault

12/10/2010 9:37 AM

If the goddam' bulb won't light, then the OP doesn't have an electrical problem to solve.

<sigh>

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply
Guru

Join Date: May 2010
Posts: 570
Good Answers: 55
#21
In reply to #12

Re: DC Battery Fault

12/10/2010 1:41 PM

How about using 10 gauge copper wire instead of the bulb? If it does not get red hot there is no problem, right?

My point being: that the bulb will not light if there is insufficient current available, but that the very small current available can nevertheless be enough to cause problems such as corrosion, battery drain, etc., even though it cannot cause a bulb to light.

This is probably nit picking, but I would rather advise that the voltage be measured across the bulb, rather than using bulb illumination alone as an indicator.

Clearly, if the bulb lights, there's a problem. If it does not light you cannot rule out a smaller problem, such as the battery cases being wet on the outside and sitting on wet ground.

__________________
Si hoc signum legere potes, operis boni in rebus Latinis alacribus et fructuosis potiri potes!
Register to Reply
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on.
Posts: 32175
Good Answers: 839
#22
In reply to #21

Re: DC Battery Fault

12/10/2010 3:31 PM

Quite.

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply
Guru
United Kingdom - Member - New Member

Join Date: Aug 2010
Location: Resting under the Major Oak
Posts: 4347
Good Answers: 181
#7

Re: DC Battery Fault

12/10/2010 8:19 AM

Davy, we assume you're using a DVM. You say you have a reading of 17V from –ve to earth, what voltage do you get from +ve to earth?

One problem with the DVM it imposes vertualy no load during a test, spurious voltages can show. Try using an analogue meter.

__________________
The reports of my death are greatly exaggerated.
Register to Reply
Participant

Join Date: Dec 2010
Posts: 3
#9
In reply to #7

Re: DC Battery Fault

12/10/2010 9:15 AM

from positive to earth there was 9v Iwas using a fluke DVM

Register to Reply
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on.
Posts: 32175
Good Answers: 839
#10
In reply to #9

Re: DC Battery Fault

12/10/2010 9:21 AM

Does the goddam' filament bulb light between -ve and earth?

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply
Guru
Canada - Member - If there is a way to screw someting up, there is someone to do so! Safety - Hazmat - New Member

Join Date: Mar 2007
Location: Iqaluit, NU. Canada
Posts: 1854
Good Answers: 140
#18
In reply to #10

Re: DC Battery Fault

12/10/2010 11:13 AM

You can lead a horse to water, but...

__________________
Joe Contractor to Electrical Inspector, "What do you mean you are going to make me follow the code?".
Register to Reply
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on.
Posts: 32175
Good Answers: 839
#23
In reply to #18

Re: DC Battery Fault

12/10/2010 3:33 PM

Well, there's enough here to drown in!

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply
Guru
United Kingdom - Member - Not a New Member Hobbies - Musician - New Member Hobbies - Fishing - New Member

Join Date: May 2006
Location: Reading, Berkshire, UK. Going under cover.
Posts: 9684
Good Answers: 468
#19
In reply to #9

Re: DC Battery Fault

12/10/2010 11:34 AM

If you have 17V from one terminal to earth, 9V from the other to earth and 24V between terminals - something doesn't add up, right?

So the 17V and 9V readings are very little, if anything, to do with leakage and a lot to do with pickup from the local radio station etc., right?

Oh, and by the way, does a 24V filament lamp light when you connect it between -ve and earth?

__________________
"Love justice, you who rule the world" - Dante Alighieri
Register to Reply Score 1 for Good Answer
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on.
Posts: 32175
Good Answers: 839
#24
In reply to #19

Re: DC Battery Fault

12/10/2010 3:34 PM
__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply
Guru
Engineering Fields - Electrical Engineering - Been there, done that. Engineering Fields - Control Engineering - New Member

Join Date: Dec 2008
Location: Long Island NY
Posts: 15600
Good Answers: 981
#11

Re: DC Battery Fault

12/10/2010 9:26 AM

You are wrong in thinking that you have anything here on Earth that is not connected to Earth. Everything around your battery provides a current path to Earth. The air between your battery terminals to Earth is the simplest path. A more complicated path is through the shell of your battery, to the paint of your stand, to the metal of the stand to the tile floor to the concrete of your building to the building ground. Now the air and the shell of your battery are likely a very high impedance path but they are still a path. Now the instrument that measured 17V from battery to Earth also has an input impedance. If the instrument's impedance and the battery voltage were known then one could make a calculation of what the minimum isolation resistance path that you have.

Compounding your problem of working with an isolated circuit is all of the interference coupling signals from AC power lines and radio transmitters that are all very tiny currents. But because these tiny currents are traveling through a high impedance path the voltage is measurable.

__________________
"Don't disturb my circles." translation of Archimedes last words
Register to Reply
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on.
Posts: 32175
Good Answers: 839
#13
In reply to #11

Re: DC Battery Fault

12/10/2010 9:43 AM

OK. Consider this hypothetical scenario:

  • A brand new 240VAC - 24VAC transformer is energised for the first time, and even if the 24VAC terminals are not connected to anything, a Fluke DVM says 17V from one terminal to earth. On de-energising and switching to ohms, the thing goes >20MΩ. Is there a problem?
  • Take the transformer away and substitute the OP's battery. Same thing happens on both volts and ohms. Is there a problem?

<sigh>

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply
2
Associate

Join Date: Nov 2010
Location: Kazakhstan
Posts: 27
Good Answers: 2
#15

Re: DC Battery Fault

12/10/2010 9:52 AM

Place the battery on wooden or glass sheet and measure again without touching the battery terminal with your finger.

Register to Reply Good Answer (Score 2)
Guru
United Kingdom - Member - New Member

Join Date: Aug 2010
Location: Resting under the Major Oak
Posts: 4347
Good Answers: 181
#16

Re: DC Battery Fault

12/10/2010 10:46 AM

To reiterate,

"One problem with the DVM it imposes virtually no load during a test, spurious voltages can show. Try using an analogue meter."
The analogue meter will impose a slight loading and stop any spurious voltages. If needs be connect a lamp between the leads of your DVM to impose a load. This follows what PWSlack has been saying you need a load to remove the spurious voltages.

__________________
The reports of my death are greatly exaggerated.
Register to Reply
2
Guru

Join Date: Dec 2010
Posts: 1686
Good Answers: 116
#20

Re: DC Battery Fault

12/10/2010 11:47 AM

There may be no visible path to earth but leaked battery acid is a good conductor. Acid attracts water, which keeps it a good conductor despite any drying effect. Go several cells to each side of the cell which is near earth. Disconnect this group from the rest of the cells. If the rest of the cells have no unexpected voltage to earth, they are well insulated - the problem is only the group you disconnected. It might be one leaking cell. If you can, get strong plastic insulating trays, floor tiles or similar and put one under each suspect cell. Trays are good because any leaked acid will be trapped in them. You may well just have a general problem of cells covered with dirt and acid (forming a conductive film), wash the sides of each cell thoroughly with distilled water. At the final trumpet, any battery which has been in use for a long time will (due to slight leakage) have some odd voltage to earth if you test with 100 megohm DVM. As another correspondent suggests, you need to connect a reasonably low resistor to earth, say 500 ohms per battery volt from a battery end to earth to find how much leakage you have. After all if the centre of 110V battery appears to be at 0 volts, this could be due to 1 megohm from each pole to earth, or 1000 ohms. The voltage would be the same but current to earth very different. The voltage could be the result of leakages (each a different resistance) from several cells You say "the bank is totally insulated from earthed parts" - but is it connected still to any other parts which might have an earth fault? Finally, you did not state the battery voltage. Maybe you have a 34 volt battery with an earth fault relay which puts the centre at earth in the absence of a fault??

Register to Reply Good Answer (Score 2)
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on.
Posts: 32175
Good Answers: 839
#25
In reply to #20

Re: DC Battery Fault

12/10/2010 3:37 PM
__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply
Guru
Popular Science - Cosmology - New Member Engineering Fields - Civil Engineering - New Member Engineering Fields - Nuclear Engineering - New Member United States - Member - New Member

Join Date: Aug 2010
Posts: 714
Good Answers: 38
#26
In reply to #25

Re: DC Battery Fault

12/10/2010 3:42 PM

Hey!!! What IF... and bear with me here... we connect a filament bulb between the negative and ground and see if it lights up?!!

__________________
Sometimes my thoughts are in a degree of order so high even I don't get it...
Register to Reply
Power-User

Join Date: Aug 2008
Location: Chicago, IL USA
Posts: 120
Good Answers: 2
#27
In reply to #26

Re: DC Battery Fault

12/10/2010 3:51 PM

That a good idea.

Register to Reply
Guru
Engineering Fields - Electrical Engineering - Been there, done that. Engineering Fields - Control Engineering - New Member

Join Date: Dec 2008
Location: Long Island NY
Posts: 15600
Good Answers: 981
#28
In reply to #26

Re: DC Battery Fault

12/10/2010 3:57 PM

Hey, what if we connect a 24V lamp across the positive and negative terminals to see if it lights up.

If the bulb lights up maybe we can now see if any other debris is connecting one of the two terminals to ground. I wonder what the voltages are across the battery with the light bulb ON and from each terminal to ground?

Maybe we should just glue a few cockroaches to this battery, put it in a missile just off the California coast, launch this to Mars and then measure the voltage to ground.

__________________
"Don't disturb my circles." translation of Archimedes last words
Register to Reply
Guru
Canada - Member - If there is a way to screw someting up, there is someone to do so! Safety - Hazmat - New Member

Join Date: Mar 2007
Location: Iqaluit, NU. Canada
Posts: 1854
Good Answers: 140
#29
In reply to #26

Re: DC Battery Fault

12/10/2010 4:15 PM

Geese... what a great idea. I am surprised no one else suggested that course of action.

LOL...

__________________
Joe Contractor to Electrical Inspector, "What do you mean you are going to make me follow the code?".
Register to Reply
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on.
Posts: 32175
Good Answers: 839
#40
In reply to #29

Re: DC Battery Fault

12/14/2010 3:08 PM
__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply Score 1 for Off Topic
Guru
Engineering Fields - Electrical Engineering - New Member United States - Member - New Member

Join Date: Apr 2007
Location: Wichita, Kansas USA
Posts: 653
Good Answers: 30
#42
In reply to #40

Re: DC Battery Fault

12/17/2010 9:18 AM

That's not Stinky Pete is it?

Register to Reply
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on.
Posts: 32175
Good Answers: 839
#44
In reply to #42

Re: DC Battery Fault

01/03/2011 8:19 AM
__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply
Guru
United Kingdom - Member - New Member

Join Date: Aug 2010
Location: Resting under the Major Oak
Posts: 4347
Good Answers: 181
#30
In reply to #25

Re: DC Battery Fault

12/10/2010 4:18 PM

Hey PWS, barbiturates usually work for me

The fault always goes away, until tomorrow

__________________
The reports of my death are greatly exaggerated.
Register to Reply Score 1 for Off Topic
2
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on.
Posts: 32175
Good Answers: 839
#41
In reply to #30

Re: DC Battery Fault

12/14/2010 3:13 PM
__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply Good Answer (Score 2)
Anonymous Poster
#31

Re: DC Battery Fault

12/11/2010 2:38 AM

Let's look at this one step at a time, starting with the obvious:

1) Is your fluke set to monitoring DC voltage? If it is set to AC it can give you bogus readings.

2) You say you get -17V at one terminal and +9 at the other. This is a difference of 26V, which would be reasonable for 24V battery being float charged.

3) With all due respect to the previous poster, in a practical sense, there is such a thing as not being grounded to earth. He is right only in the theoretical sense. What I suspect you have is a floating ground. The voltage difference in the battery only makes sense referenced between the terminals. If the negative terminal is not connected to ground, then earth ground and battery ground can and will have a random voltage difference.

4) When I hear "battery bank" I immediately suspect it is connected to something, such as your house wiring. Now you can get into all sorts of problems such as nicks in the wires or ground faults. One of the most common is an improperly installed neutral wire. Stick your meter (check both AC and DC) into the ground and neutral connections. If you get a voltage, you probably have a problem with your neutral or with your ground.

The problem with trying to diagnose these things remotely is that we can't see exactly what you are talking about, and the info you provided was sketchy.

Register to Reply
Guru

Join Date: Dec 2010
Location: North West England
Posts: 1170
Good Answers: 153
#32

Re: DC Battery Fault

12/11/2010 5:20 AM

31 comments and nobody has seen the light. There is no battery fault. If the battery is really disconnected from earth, the DVM/earth test forms the only link, all be it very high impedance. The negative terminal would float up to earth potential and 0v would be recorded. Equally,when testing the positive terminal, it would float down to earth potential and 0v would again be registered.

So why are you getting "consistent" (How many times did you do the test?) readings of 17v and 9v. This suggests that there is a different resistance between the +v/earth test and the -v/earth test. The DVM is common so that can be eliminated. The only things left are the terminals (are they clean?, have you tried scraping off any oxide layer?) and the earth(are you testing to the same earth point?)

One last question. Why is the battery voltage floating? Floating voltages are notoriously difficult to fault find and there is rarely any advantage to using them. All you need is 24V between the two terminals. Deliberately tie one terminal to ground and the "problem" goes away.

Register to Reply
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on.
Posts: 32175
Good Answers: 839
#43
In reply to #32

Re: DC Battery Fault

01/03/2011 8:13 AM

<...31 comments and nobody has seen the light....>

Would that light be coming from a 24V filament lamp?

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply
Guru

Join Date: Feb 2010
Posts: 1013
Good Answers: 36
#33

Re: DC Battery Fault

12/11/2010 5:29 AM

I cannot explain this!

There are so many unknown and you have received a lot of replies indicating procedures to follow and return with some answers.... You did not reply to any of the suggested tests!!

One More: Disconnect the bank terminals from any connected charger or load, just the battey by itself, and then do the voltage test with the DC range on your DVM, also the lamp test checking the current drain even if the lamp does not light up. --> you should get no readings except some very negligeable (~1V dc??) which will not show any current flow (microamps??). The negligeable will be due to stray pickups that your DVM will get when the leads will act as antenae...

With the above test, if you pick up any substantial current (any where near 10mA and above), then you might be just pulling our legs..

Register to Reply
Guru

Join Date: May 2010
Location: in optimism
Posts: 4050
Good Answers: 130
#34
In reply to #33

Re: DC Battery Fault

12/11/2010 7:07 AM

A battery is a pretty good capacitor - try thinking in those terms

__________________
There is no sin except stupidity. (Oscar Wilde, Irish dramatist, novelist, & poet (1854 - 1900))
Register to Reply
Guru

Join Date: Feb 2010
Posts: 1013
Good Answers: 36
#35
In reply to #34

Re: DC Battery Fault

12/11/2010 10:33 AM

Yes in terms of holding some charge. But it works differently since the 2 poles are immersed in an electrolite that is conductive. Yes we can sometimes look at it as a big capacitor in terms of charges.

In this case, the only capacitor will be between the internal part with the conductive electrolite, and the outside of the casing if we stic some conducting film etc.

But the charging will be very small due to the thickness of the dielectric (Case plastic) and the 24V potental. Even this voltage is only between the extreme poles as mentioned by the OP.

I do not think that there will be enough charge to give a voltage of 17 DC between the Negative and an isolated earth / ground point.(In fact between any of the 2 poles for this matter... think of it).

In any case, if it is a capacitive charge, it will discharge quickly and zero if any pole is shorted (via a lamp foe ex.) to the ground... The OP is not giving a clear complete picture of the circuit he is looking at to obtain such voltages as mentioned!

Register to Reply
Guru

Join Date: May 2010
Location: in optimism
Posts: 4050
Good Answers: 130
#36
In reply to #35

Re: DC Battery Fault

12/11/2010 3:52 PM

Most battery banks are wood pallets or tables because batteries discharge quite quickly sitting on concrete. That sort of capacitance and a bit of acid would explain this - I feel.

__________________
There is no sin except stupidity. (Oscar Wilde, Irish dramatist, novelist, & poet (1854 - 1900))
Register to Reply
Guru
Engineering Fields - Electrical Engineering - Been there, done that. Engineering Fields - Control Engineering - New Member

Join Date: Dec 2008
Location: Long Island NY
Posts: 15600
Good Answers: 981
#37
In reply to #36

Re: DC Battery Fault

12/11/2010 4:13 PM

The only battery system I've ever maintained all resided in my automobile. But it makes no sense to me that concrete would make any difference to the charge of a battery. Now I can see that the low cost and low reactivity to acids could make wood a more suitable support material than concrete or metal. I've recently seen a large capacitor bank that all of the batteries sat in long Nalgene® tubs as a secondary containment vessel.

__________________
"Don't disturb my circles." translation of Archimedes last words
Register to Reply
Guru

Join Date: May 2010
Location: in optimism
Posts: 4050
Good Answers: 130
#38
In reply to #37

Re: DC Battery Fault

12/11/2010 4:44 PM

A similar effect you may be more familiar with, is a sheathed element (as in stove, or kettle, or water heater)

If you don't ground the sheath, it will float at half the supply potential (with enough current available to wreck sensitive instruments)

Obviously the dielectric strength of the filler is adequate to resist (several times) the supply potential, so it's not a 'leakage' problem. And it's 'one shorted turn' magnetically.

__________________
There is no sin except stupidity. (Oscar Wilde, Irish dramatist, novelist, & poet (1854 - 1900))
Register to Reply
Guru

Join Date: Feb 2010
Posts: 1013
Good Answers: 36
#39
In reply to #38

Re: DC Battery Fault

12/12/2010 5:48 AM

Yes, but the battery is DC and does not induce any current in any metal nearby.

The Capacitance will have to be: The internal Plates as one pole (Positive and negative), thwe electrolite as Dielectric (-?-) and the plastic container as a further dielectric, and then any nearby conductor as the external Capacitor pole. I don't think this is going to give any similar result as by the OP.

Most probably, he has some devices connected to the battery (charger, others as loads...) and the leak to ground is though them.

Register to Reply
Register to Reply 44 comments

Good Answers:

These comments received enough positive votes to make them "good answers".

"Almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, vote them!
Copy to Clipboard

Users who posted comments:

34point5 (3); 67model (1); Anonymous Poster (1); ChaoticIntellect (1); davyrascal (2); dkriley (1); Gizma (1); Happy singh (1); jhhassociates (1); JohnDG (2); kramarat (1); LAA_Lucke (3); MoronicBumble (1); North of 60 (2); PWSlack (15); redfred (3); rhkramer (1); tdesmit (1); TonyS (3)

Previous in Forum: Type Test Report of Battery   Next in Forum: DC Chopper
You might be interested in: Battery Holders, Battery Chargers

Advertisement