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Old 08-06-2012, 11:41   #46
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Re: Battery Cabling for Parallel Bank

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Originally Posted by Jbaffoh View Post
Ok, now I'm confused.

If changes in voltage that accompany changes in charge modes are solely a function of charger current changes, then why do I observe this in my setup? My solar controller will bring the batteries to 14.5 at around 3.5 amps (depending on solar energy). After absorption, the voltage drops to around 13.4, while the current remains around 3.5 amps. As the voltage rises to 13.52, the current begins to taper down near zero.
EGGZAKTLY.
As the voltage rises to 13.52 the charger lowers the current to near zero so that the voltage will not rise too high. The current flowing is the CAUSE, the voltage you see is the EFFECT. The charger regulated the current to achieve that result.
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Old 08-06-2012, 11:49   #47
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Re: Battery Cabling for Parallel Bank

Quote:
Originally Posted by Jbaffoh View Post
Ok, now I'm confused.

If changes in voltage that accompany changes in charge modes are solely a function of charger current changes, then why do I observe this in my setup? My solar controller will bring the batteries to 14.5 at around 3.5 amps (depending on solar energy). After absorption, the voltage drops to around 13.4, while the current remains around 3.5 amps. As the voltage rises to 13.52, the current begins to taper down near zero.
This could be a pwm system , and hence you may need a scope to see whats actually happening

Dave
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Old 08-06-2012, 12:06   #48
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Re: Battery Cabling for Parallel Bank

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Originally Posted by Andina View Post
EGGZAKTLY.
As the voltage rises to 13.52 the charger lowers the current to near zero so that the voltage will not rise too high. The current flowing is the CAUSE, the voltage you see is the EFFECT. The charger regulated the current to achieve that result.
Andina I don't think anyone is disputing the charger sets the voltage by modifying the current. This means the charger sets, or adjusts the battery voltage to an appropriate value.
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Old 08-06-2012, 12:10   #49
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Quote:
Originally Posted by Andina
EGGZAKTLY.
As the voltage rises to 13.52 the charger lowers the current to near zero so that the voltage will not rise too high. The current flowing is the CAUSE, the voltage you see is the EFFECT. The charger regulated the current to achieve that result.
I'm not challenging you--I lack the EE credentials. But I remain confused because you haven't addressed the drop from 14.5 volt absorption to 13.5ish float mode WHILE THE CURRENT INITIALLY REMAINS THE SAME. My voltage drops to float levels several minutes, usually 10-20, before the current begins to taper.
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Old 08-06-2012, 12:13   #50
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Originally Posted by goboatingnow

This could be a pwm system , and hence you may need a scope to see whats actually happening

Dave
Yes, it is.

The late 50's/early 60's Techtronic scope I used for biasing my vintage tube guitar amplifiers is a little cumbersome to bring on the boat
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Old 08-06-2012, 12:17   #51
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Re: Battery Cabling for Parallel Bank

Quote:
Originally Posted by Jbaffoh View Post
I'm not challenging you--I lack the EE credentials. But I remain confused because you haven't addressed the drop from 14.5 volt absorption to 13.5ish float mode WHILE THE CURRENT INITIALLY REMAINS THE SAME. My voltage drops to float levels several minutes, usually 10-20, before the current begins to taper.
The current into the battery has to drop, if the charger is to reduce the battery voltage.( for a lead acid battery)
It may be that you are seeing a display of the chargers total current, including loads, so the drop in current for the battery is not noticeable.
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Old 08-06-2012, 12:29   #52
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The current into the battery has to drop, if the charger is to reduce the battery voltage.
It may be that you are seeing a display of the chargers total current, including loads, so the drop in current for the battery is not noticeable.
Well, it IS a PWM charger on a 50-watt panel, so there are fluctuations in current during bulk and absorption that I attribute to changes in solar energy from passing clouds, etc. it's not as though my meter is reading a constant 3.5 amp supply from the charger.

But there is a point after the voltage drops from 14.5 to 13.4-5ish, when the current suddenly plummets from 2.8-3.3 range, in one move, to 1 amp or below. Then it gradually tapers to zero-ish.

This is with no load other than my stereo presets and the linkpro monitor.

I'm just curious, not trying to claim anybody is wrong.
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Old 08-06-2012, 13:08   #53
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Re: Battery Cabling for Parallel Bank

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Originally Posted by Jbaffoh View Post
.

But there is a point after the voltage drops from 14.5 to 13.4-5ish, when the current suddenly plummets from 2.8-3.3 range, in one move, to 1 amp or below. Then it gradually tapers to zero-ish.
.
This is what should happen, but the current drop and the voltage drop should be simultaneous. The voltage drops, because the current drops. Some meters have a slight delay to smooth out the display, but it should not be more than a few seconds, at most.
The battery voltage has some "inertia" so after the transition from absorption to float the current will sometimes rise slightly as the controller maintains the constant float voltage, but the current will then fall as the battery becomes more charged.
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Old 08-06-2012, 13:14   #54
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Re: Battery Cabling for Parallel Bank

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" it will accept the same current from a 40 amp charger as a 400 amp charger set at the same voltage. "


On a discharged battery a 400 amp charger will put out a hell of a lot more current than a 40 amp charger and a 15 amp charger will charge a lot faster than a 5 amp charger.
Andina

You quoted only part of what I posted. I said "As long as the battery is not demanding more than the source can supply it will accept the same current from a 40 amp charger as a 400 amp charger."

example: 100 AH flooded battery. Its max acceptance in bulk will be about 25 amps. As long as both chargers can output the 25 amps the battery will accept a larger charger will not charge the battery faster, assuming the same set points for bulk mode.
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Old 08-06-2012, 13:49   #55
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Re: Battery Cabling for Parallel Bank

what Andina meant is that assuming the acceptance charge is above the smallest charger , the 400 amp will charge faster then the 40

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Old 08-06-2012, 16:28   #56
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Re: Battery Cabling for Parallel Bank

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I know you guys in Lonnie have an aversion to the big smoke down south and the apple eating fellas down south will run you outa town like faceless devil if they spot you but perhaps you could wombat down and get your wire in Hobart
Gee Wotname, are you suggesting I drive down SOUTH?
What shop is in Hobart you'd suggest I can get it at?
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Old 08-06-2012, 16:34   #57
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Re: Battery Cabling for Parallel Bank

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Here is a good place to start:
American wire gauge - Wikipedia, the free encyclopedia
and perhaps better
AWG to square mm Wire Gauge Conversion

It essence, most electrical wire in Australia is sold in metric cross sectional area (e.g 6 sq mm) but it can be found in AWG (or B&S) in specialised industries like aviation and marine. Whitworths Marine sell smaller wire in cross sectional mm and battery cable in B & S (AWG).

See https://www.whitworths.com.au/main_l...=Battery+Cable
Brillant! thanks, this is what I needed. I want to use Tinned wire as battery cable and the young guy at my local shopt told me you can't get tinned battery cable. I'd already seen it advertised at whitworths, but didn't know what size to go for. so this helps heaps. I'm planning on using all the same cable, so I need to make it heavier enough for the starter cable as well, when I have it worked out. cheers.
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Old 08-06-2012, 16:42   #58
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Re: Battery Cabling for Parallel Bank

After reading this am I right in thinking number 2 only does up to 130amps though? Is this big enough?
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Old 08-06-2012, 17:27   #59
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Re: Battery Cabling for Parallel Bank

Quote:
Originally Posted by Wotname View Post
Here is a good place to start:
American wire gauge - Wikipedia, the free encyclopedia
and perhaps better
AWG to square mm Wire Gauge Conversion

It essence, most electrical wire in Australia is sold in metric cross sectional area (e.g 6 sq mm) but it can be found in AWG (or B&S) in specialised industries like aviation and marine. Whitworths Marine sell smaller wire in cross sectional mm and battery cable in B & S (AWG).

See https://www.whitworths.com.au/main_l...=Battery+Cable
Beware of the whitworths cable sizes, their 4mm cable for eg. is really 1.84 sq.mm. The 4mm may be the diameter ? Both sizes are on the cable drum but the catalogue lists it as 4mm. Auto cable is also in mm not sq.mm.
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Old 08-06-2012, 18:33   #60
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Re: Battery Cabling for Parallel Bank

Ted

2 awg will actually handle 178 amps in an engine compartment.

But the larger issue is distance - the less voltage drop the better. Here's a link to a good calculator. AWG by wire length/amps calculator
Just plug in the numbers and the answer appears at the bottom.
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