Wire gauge recommendation

[johnm1]

To get the most efficent charging to my batteries, with cost kept in mind, what wire gauge should I use between the batteries and charger?

I have a pair of 6v gc batteries.
They're about 12-15 feet from the charger.
I have a Boondocker 75A charger.
Currently have 6awg wire with very good crimped battery lugs.

Thanks

[Chum_lee]

Not my opinion. Info from NEC and Interstate Battery Co. (please no adverse comments if you don't like Interstate Batteries) Info is provided for reference only.

www.batteries-faq.com/activekb/questions.php?questionid=1

www.jade1.com/jadecc/courses/UNIVERSAL/graphics/large/QID3144_large.jpg

The manufacturers (Interstate in this case) suggested charge rate is C/10 amps. C = 20 hour capacity in Amp-hours. For the given 12 volt application Interstates recommended initial bulk charge rate is 23.2 amps. Other mfgrs. recommendations are similar but may be more or less for their flooded lead/acid battery applications.

Yes, the battery bank (2 - 6 volt deep cycle batteries in this case) will accept 75 amps for a while before they start to heat up excessively off gassing hydrogen and oxygen. (an explosive mixture) If not quickly vented to the atmosphere and if it finds an ignition source it WILL blow the tops off the batteries and spew H2SO4 everywhere. (including your face, eyes, clothes, etc. if you are too close) The plates may still be functional though if you add more electrolyte.

As the state of charge comes up, the charging amps WILL taper so IMO the charge rate and related voltage drop in the wires is largely a moot point. (if the charger is set to automatic mode)

Many things can happen with excessive off gassing. If the OP is not around, the propane detector solenoid can trip, BUT the battery bank keeps off gassing. (charging) If the batteries (like mine) are mounted under the entry stairs or in a poorly vented compartment where gas can collect inside or below the MH, . . . . Can you say BOOM? In my 50 years of experience I have personally seen this happen, . . . . more than once!

That's why the nerdy engineers limit the suggested charge rates. (to protect those people who DON'T know any better) Those who DO know better are not subject to their charts.

If it can happen, it eventually will! (to somebody)


Chum lee

[time2roll]

grizzzman wrote:
So......The Boondocker is exactly like the WFCO? Is that you are saying?

No not at all. See the graph. Boondocker will boost charge to the level shown based on the battery capacity to charging amp ratio. Graph is for 220 amp/hours or about 2x GC2 or 2x G27. Just pick charging amps and slide over to the graph where Boondocker will drop to boost.


WFCO will generally just trickle charge the entire time.

[grizzzman]

grizzzman wrote:
Additionally I suggested he add a 4awg to his factory 6awg giving him a wire diameter of about 2/0 not 2.........

[grizzzman]

Oops

[grizzzman]

smkettner wrote:

grizzzman wrote:
If the converter is outputting 14.6 then with the voltage drop "correctly" delt with would not the voltage at the battery be at least close to 14.6?

75 amps through #6 wire is 0.914 volts drop. Frame ground might be a bit better but you also have connections that add a bit. So with so 0.7 drop in the circuit the supply will be 14.6 and the load (battery) is 13.9 volts. 15 minutes later the Boondocker is at 13.6 volts.

#4 shows 0.575 drop so maybe 14.2 on the battery before that timer starts.

Now try 35 amp version....

0.427 drop with #6 and 0.268 drop with #4. This gives more time at a higher voltage and you end up at a higher state of charge before the voltage kicks down.

http://www.genuinedealz.com/voltage-drop-calculator

Member BFL13 ran these tests constantly and posted graphs all the time. I did similar testing to get my WFCO-55 into boost mode. I ended up with about 20' of #2 into four GC2 and it was still hit or miss to get the voltage low enough for long enough to trigger boost.



(credit to BFL13)

I sure miss BFL13.... And yes I have seen the famous " ugly" graph many times. Seems to me you missed the "with the voltage drop "correctly" delt with" part perhaps? So......The Boondocker is exactly like the WFCO? Is that you are saying?

[time2roll]

grizzzman wrote:
If the converter is outputting 14.6 then with the voltage drop "correctly" delt with would not the voltage at the battery be at least close to 14.6?

75 amps through #6 wire is 0.914 volts drop. Frame ground might be a bit better but you also have connections that add a bit. So with so 0.7 drop in the circuit the supply will be 14.6 and the load (battery) is 13.9 volts. 15 minutes later the Boondocker is at 13.6 volts.

#4 shows 0.575 drop so maybe 14.2 on the battery before that timer starts.

Now try 35 amp version....

0.427 drop with #6 and 0.268 drop with #4. This gives more time at a higher voltage and you end up at a higher state of charge before the voltage kicks down.

http://www.genuinedealz.com/voltage-drop-calculator

Member BFL13 ran these tests constantly and posted graphs all the time. I did similar testing to get my WFCO-55 into boost mode. I ended up with about 20' of #2 into four GC2 and it was still hit or miss to get the voltage low enough for long enough to trigger boost.



(credit to BFL13)

[MEXICOWANDERER]

MANUALS ARE WRITTEN BY PEOPLE WHO THINK...

Boondocking means Boondocks, the place they end up at when they take a wrong turn in the country.

Their brains are glued tight to the idea that their batteries are welded solid to a power pole connection.

Discharge the batteries, Yeah! Then recharge using gentle current FOR AS LONG AS IT TAKES. Power is available 24/7 in their brainless little world.

If I made batteries and sold them I would insist they be babied to the max. It would sure make my batteries look good. RECHARGE BATTERY BEFORE STARTING ENGINE OR WARRANTY IS VOID decals belong in the same category.

I don't live in an ideal world nor vacation in the Waikiki Hilton. Ask 50 lead acid battery engineers if they "Boondock" and to a man they will answer "Huh? You nuts?"

I will say this again and again. I REFUSE TO SPEND THREE HUNDRED DOLLARS IN ORDER TO GAIN SIX WEEKS OF EXTRA BATTERY LIFE. Or three weeks, or whatever. It's chasing nickles with dollars. Not exactly smart.

Oooooooooooo it'll burn up the battery!

Somwhere deep inside a 160 or 270 ampere alternator is a mystic clandestine circuit that detects and automatically adjusts (limits) current to baby hyper-sensitive batteries. You can read the Appendix of Snow White, or The Three Little Pigs to verify this.

Instead of GUESSING, do your own tests. By cell temperature verification and physical observation (cell electrolyte electrolysis) I'd LOVE to hear from anyone that can show me a 14.8 voltage limited charge rate at 35C temp that would "damage" a battery. I have too much experience with this, including longevity proof to fall for nonsensical assumptions.

NO! 14.8 volts is NOT maintained for the entire charge cycle. I scream INTERMATIC TIMER and all I hear is an echo. It takes ONE SINGLE SOLITARY TIME to establish how many minutes it takes to reach the point of 2 bubbles per second. The timing is repeated by brain memory forever after. So what if it's five minutes, fifteen minutes too much? Think the battery is going to overheat or blow up?

Ninety five percent of corporate battery plant engineers operate 100% by ROTE (look the word up).

By circling them, biting them in the ass, and solving their "unsolvable" dilemmas, I made a sizeable chunk of change in thirty years.

So when these folks come out with "mandatory" theoretical limits for consumers, I laugh. 99.9% is theoretical ROTE. Yes, a soft charge rate will indeed afford increased battery life. But they haven't the faintest idea as to how much because they have never done the testing. Ask a "battery engineer" what the ideal alternator charge rate is for an automotive environment as you will hear "But but but that's DIFFERENT!". Facts are They Do Not Know. They bombast with bluster.

And people have little choice but to believe all this.

BATTERY MUST BE RECHARGED BEFORE STARTING ENGINE OR ALTERNATOR WARRANTY IS VOID

[grizzzman]

smkettner wrote:
I am not sure who recommended 75 amps for two batteries or a Boondocker for charging on generator.

Bigger wire will make a measured improvement. Trouble is the Boondocker will drop to normal mode 15 minutes after the voltage at the converter reaches 14.6 volts. This might be 14.0 volts at the battery, maybe less. In effect boost goes to about 70% charged. This might seem odd but the 35 amp would have been better because it would have boosted into a higher state of charge. Fine for utility power and lots of time, not so much on generator. And yes still better than WFCO.

Give it a test but if Randy would trade it for a 9260 or IOTA-DLS-45 I think you would be better off. The #6 is fine if the converter holds boost mode.

75 amps available will not hurt the battery one bit as the voltage is well within the recommended limit.

If the converter is outputting 14.6 then with the voltage drop "correctly" delt with would not the voltage at the battery be at least close to 14.6?

[grizzzman]

Calkidd wrote:
Wire size graph

FYI does not work.

[time2roll]

I am not sure who recommended 75 amps for two batteries or a Boondocker for charging on generator.

Bigger wire will make a measured improvement. Trouble is the Boondocker will drop to normal mode 15 minutes after the voltage at the converter reaches 14.6 volts. This might be 14.0 volts at the battery, maybe less. In effect boost goes to about 70% charged. This might seem odd but the 35 amp would have been better because it would have boosted into a higher state of charge. Fine for utility power and lots of time, not so much on generator. And yes still better than WFCO.

Give it a test but if Randy would trade it for a 9260 or IOTA-DLS-45 I think you would be better off. The #6 is fine if the converter holds boost mode.

75 amps available will not hurt the battery one bit as the voltage is well within the recommended limit.

[EsoxLucius]

Calkidd wrote:
Wire size graph

What a mess of BBCodes! And that graph is pathetic. Use a real calculator.

[Calkidd]

Wire size graph

[grizzzman]

MEXICOWANDERER wrote:
Sorry Almot.

GC220's will eat 80 amperes and not even burp. Or maybe the several thousand GC220's I configured charging sources for were "lucky"

The distributor I worked for was Trojan's largest. I came up with a series charger utilizing 60 amperes which vf'd to 7.5 volts and change.

Or maybe it would be wise to not use that 160-amp underhood alternator to recharge house batteries altogether.

I would not hesitate a microsecond to use a 150 ampere rated charger on a pair of GC batteries. For every battery that dies a few weeks early due to fast charge positive plate erosion, 10,000 batteries die of hardened sulfation.

Power pole princess rigs can get away with a 20-amp charger feeding two dozen GC220 batteries. It's when boondocking charging comes into play that rational charging levels should help to defer premature generator wear-out and fuel trips bankruptcy.

Shore is nice spending three hundred needless dollars in toad fuel to extend battery life six-months.

If an individual disagrees with this, when max charging, run an infrared pyrometer across the batteries. Then open the caps (goggles) and check the electrolyte for gassing.

I have stated on this forum for years, at 25C, charge 5% antimony batteries at 14.8 volts limit. When bubbles increase more than 2 per second reduce charging and let the double-digit IQ "Smart" Charger take over.

Many a pair of T-105's have taken 88 amperes. My job was to minimize warranties for the distributor. My philosophy worked. Nothing as pleasant as a repeat customer with a smile on his (her) face.

Johnm1 READ what this old er well you know :W person says. Go with at least 4awg keep the 6 awg (if redundant power systems are OK with NASA why would it not be for your rv?) The frame is fine in most case's . Remember it is the distance that causes the voltage drop short runs to the frame "may" be OK with 6awg. While charging at 75 amps check the voltage at the converter and at the batteries. For the "most" efficient charging (remember you asked) They should match.

[Almot]

johnm1 wrote:
Would adding 2 more batteries help?

2*6V need 45A, 4*6V need 90V. The former will have too much current @75A, the latter will be charging slower.

Mex - 2*GC will eat 80A but the manual says not to let them eating that much :). You proved them wrong, but they haven't changed the manual. I hear what you're saying on usage pattern, occasional and shallow VS deep cycling.

[MEXICOWANDERER]

Sorry Almot.

GC220's will eat 80 amperes and not even burp. Or maybe the several thousand GC220's I configured charging sources for were "lucky"

The distributor I worked for was Trojan's largest. I came up with a series charger utilizing 60 amperes which vf'd to 7.5 volts and change.

Or maybe it would be wise to not use that 160-amp underhood alternator to recharge house batteries altogether.

I would not hesitate a microsecond to use a 150 ampere rated charger on a pair of GC batteries. For every battery that dies a few weeks early due to fast charge positive plate erosion, 10,000 batteries die of hardened sulfation.

Power pole princess rigs can get away with a 20-amp charger feeding two dozen GC220 batteries. It's when boondocking charging comes into play that rational charging levels should help to defer premature generator wear-out and fuel trips bankruptcy.

Shore is nice spending three hundred needless dollars in toad fuel to extend battery life six-months.

If an individual disagrees with this, when max charging, run an infrared pyrometer across the batteries. Then open the caps (goggles) and check the electrolyte for gassing.

I have stated on this forum for years, at 25C, charge 5% antimony batteries at 14.8 volts limit. When bubbles increase more than 2 per second reduce charging and let the double-digit IQ "Smart" Charger take over.

Many a pair of T-105's have taken 88 amperes. My job was to minimize warranties for the distributor. My philosophy worked. Nothing as pleasant as a repeat customer with a smile on his (her) face.