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 > Talk about voltage drop (12v)

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CA Traveler

The Western States

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Joined: 01/03/2004

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Posted: 08/03/21 07:22pm Link  |  Quote  |  Print  |  Notify Moderator

wopachop wrote:

I'm seeing voltage drop along the wire correct? Not battery sag? The test is during the day with solar hooked up. Only drawing 3amps. Measure the battery voltage at the posts under load to determine wire vs battery voltage drop.

Why dont I see similar voltage drop while on shore power? Pretend the Led display read 14v. When I apply the same 3a load why doesnt the display show 12-13 volts? Your charger can supply many more amps for house loads and battery charging including the inverter amps.

I understand that higher voltage sags less. But we are only talking the difference of 12v boondocking to 14v on shore power.


You stated old batteries - Have them load tested, then consider deep cycle batteries - Marine batteries are a modified starting battery, not so much deep.

Clarification: Your charging sources supply power to all house load FIRST and that includes appliances that can't be turned off like smoke dedectors etc. What's left is used to charge the battery.

150W solar is light. It might be 5A+ in bright direct sun and less otherwise.


2009 Holiday Rambler 42' Scepter with ISL 400 Cummins
750 Watts Solar Morningstar MPPT 60 Controller
2014 Grand Cherokee Overland

Bob


pianotuna

Regina, SK, Canada

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Posted: 08/03/21 07:25pm Link  |  Quote  |  Print  |  Notify Moderator

14 to 12 is a 15% difference


Regards, Don
My ride is a 28 foot Class C, 256 watts solar, soon to have SiO2 batteries, 3000 watt Magnum hybrid inverter, Sola Basic Autoformer, Microair Easy Start.

Matt_Colie

Southeast Michigan

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Posted: 08/03/21 07:32pm Link  |  Quote  |  Print  |  Notify Moderator

Wopachop,

If you have been reading the charts, they are all wrong.....

First off, the existence of a 12V system is between 12.0 and 12.6...
All the published chart are for 3% voltage drop and that is just plain BS. Voltage drop is not %. It is millivolts. All your inverters and sensitive stuff doesn't care about drop between there and the battery bank, all they care about is what they are seeing right now. If you didn't buy enough copper, they tell you that the battery is no good.

I wish I could tell you where to get the charts I work with when I am quoting a DC job, but it is old. Like berry juice on parchment old. As soon as you have troubles, up size the copper.

Matt


Matt & Mary Colie
A sailor, his bride and their black dogs going to see some dry places that have Geocaches in a coach made the year we married.


CA Traveler

The Western States

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Posted: 08/03/21 07:33pm Link  |  Quote  |  Print  |  Notify Moderator

11.8V suggests you are drawing more house amps than the solar is supplying and more amps are being used than the battery can also supply hence the low voltage. This can also suggest discharged or weak batteries, so have them load checked.

Assume you have a 30A charger. Inverter 3A is 10%, leaving the charger to supply 27A for house and battery and kick the voltage up to 14.4V to charge the battery. Small solar not so much.

2oldman

NM

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Posted: 08/03/21 08:38pm Link  |  Quote  |  Print  |  Notify Moderator

old batteries

wopachop

Who run bartertown

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Posted: 08/03/21 08:56pm Link  |  Quote  |  Print  |  Notify Moderator

Thanks everyone. Absorbing it all.

The solar display is showing 13.x volts. So it cant be battery sag, right?

enblethen

Moses Lake, WA

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Posted: 08/03/21 09:46pm Link  |  Quote  |  Print  |  Notify Moderator

If you have a DC amp probe measure the 12 volt side or is that where you are getting 2.99 amps


Bud
USAF Retired
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2003 Chev Ice Road Tracker


wopachop

Who run bartertown

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Posted: 08/03/21 10:39pm Link  |  Quote  |  Print  |  Notify Moderator

Yes the clamp meter in the picture is measuring amps to the USB panel thing and also the small inverter.

It's dark now. The solar display and the USB display are close to equal.

This is tricking me. How can my solar display show 13v and my USB is down in the elevens?

enblethen

Moses Lake, WA

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Posted: 08/04/21 06:23am Link  |  Quote  |  Print  |  Notify Moderator

The USB device is converting 12 volts SC to 5 volts.
Wire is too small, there is a poor splice or connection or other load.
Could try running new wire to bypass the wiring in question.

wa8yxm

Davison Michigan (East of Flint)

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Posted: 08/04/21 05:20pm Link  |  Quote  |  Print  |  Notify Moderator

Why do you not see a like voltage drop on shore power????

Ok, short story
My rig had TWO shore chargers both 80 amps one was a good 50 feet electrically from the batteries and I think about 4GA wire most of the run. The other was 00 ga and perhaps 4 feet tops.
Attached to the battery about 30 feet of #1
My radio, in Transmit sucks perhaps 10 amps tops (Likely less) 50 watts RF
The main charger (The one 50 feet back) the voltage drop was too high, I had to turn on the front charger (inverter charger module) to run 50 watts.

I had a LOT of battery..

I still have that radio, and half the batteries and the 80 amp charger module in the inverter.. Just now it's closer to the batteries. So is the radio.

How much current was being delivered to the batteries by the solar? It might not have been enough. the shore power charger puts out as much as 14.6 volts and the last two digits of the model amps (mine was an xx80)


Home was where I park it. but alas the.
2005 Damon Intruder 377 Alas declared a total loss
after a semi "nicked" it. Still have the radios
Kenwood TS-2000, ICOM ID-5100, ID-51A+2, ID-880 REF030C most times


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