Talk about voltage drop (12v)

[wopachop]

Have the trailer in boondocking mode. Some old batteries and 150w of solar. The batteries are showing 13v. I have a little 300w inverter to charge my laptop and things. 14 gauge wire is feeding the little inverter and the USB panel.

Doesnt that seem weird its dropping below 12v and only pulling 3amps?

[wa8yxm]

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)

[enblethen]

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.

[wopachop]

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]

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

[wopachop]

Thanks everyone. Absorbing it all.

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

[2oldman]

old batteries

[CA_Traveler]

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.

[Matt_Colie]

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

[pianotuna]

14 to 12 is a 15% difference

[CA_Traveler]

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.

[wopachop]

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.

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?

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

[wa8yxm]

300 watts is about 30 amps at the battery 14GA is good for half that at 120 volt and even less at 12 volt due to voltage drop.

Plus there is a voltage drop INTERNAL to the batteries (I do not know how much)

The key to battery/inverter is three fold
One, Keep the leads as short as you can but do not mount the inverter inside the same space as the batteries

Two HEAVY cable for a 300 watt Starter cable works very well and is low cost up to around 750 watts it works well. long about 1000 it might be a bit...er.. anemic

3: for as much of the run tape or wire loom the cables like this ============
Side by side. This is more important on larger inverters.

AND MORE battery never hurts..

DEEP CYCLE batteries work best for House use.
(As opposed to MARINE/deep cycle) note how I use case on those)

[pianotuna]

#10 wire would be much better. I would expect 7.5% voltage drop with 15 feet of #14 and the loads.

[enblethen]

The meter and LEDs add to the load. There is losses within the unit that draws power.