Question about inverter use and power draw on batteries

[tfirma]

I will apologize right off the bat - this is both probably a newbie question - and also a bit convoluted.

So my brand new 1995 Lance has two 12v outlets... I was trying to run a 150W inverter or a 300W inverter - and having all sorts of trouble just running a macbook off the inverter (85W, I believe) I got about 5 different ideas on the issue (everything from "the wiring isn't outfitted for anything significant" to "it should all work fine" which was right from Lance themselves). Finally, the dealership did call me and said the one receptacle is "charging only" - which apparently means it doesn't have the capacity to run ANYTHING significant besides the smallest of electronics. So I focused on the other receptacle for the TV. Lo and behold, I had more luck with that. I COULD power the Laptop...but something strange is happening for which I'd love to get an explanation....

I've got two 12V batteries wired in parallel and a 160W solar package. The solar charge controller reads 100% (which I thought was the level of battery power remaining?) - but then, of course, there is also the meter reading panel for the tank levels, and battery power on the kitchen wall. Electric power has been at 100% - since I really haven't used too much power for too long...just testing things out and using some lights and occasionally the heat. (and I'm not plugged into shore power) HOWEVER - when I ran my notebook - I noticed both the reading on the solar controller went down VERY quickly (within just a few minutes, it was down to 81) AND the meter for battery strength went down to 3/4 and then even 1/4. I assumed that the drain on the batteries was just TREMENDOUS for the levels to go down so quickly. That would surprise me - I realize running off the batteries will drain them - but I can't believe it's THAT fast? But here is the stranger part. I turned off the inverter...and within about 5 minutes... I was back up to 100% on the charge controller AND on the battery meter level reading. I can't imagine the solar could help out that much that quickly - because it was raining all day and not a hint of the sun was out during all of this. I also can't imagine the drain on the batteries could be THAT substantial and so rapid for only using a 150W inverter for about 3 minutes..... But then, since the levels seemed to go right back to 100%, I'm wondering if something else is going on -- or those readings maybe mean something else?

I tried my best to describe the scenario. So the two questions are :
- Is the reading on the solar charge controller (GoPower) the actual percentage of battery power left, or something else related to the panels?
- Is it possible that just using my laptop on a 150W inverter for less than 5 minutes would drop that percentage to 81% AND the battery meter reading to almost 1/3?
- Why would both levels on both meters go right back up to 100% after about a minute of unplugging the inverter?

Thank you so much in advance!

Tom

[tfirma]

This is great, thanks so much for posting this!

pianotuna wrote:
This is what is balanced and best for twin twelve volt batteries.

[pianotuna]

This is what is balanced and best for twin twelve volt batteries.

[MEXICOWANDERER]

End result.
It's the voltage the inverter is seeing at any load. Even my Blue Seas sockets are really only good for 15 amperes without the socket and plug heating up. The included Samlex pigtail for their 300 watt inverter is the same way, try and get 300 watts and the lighter socket connection is going to scream bloody murder, and do a Lucas Electric Ltd.

[wa8yxm]

Most 12 volt outlets are wired for no more than 10 amps. and even then the voltage drop may be considerable, For conversion from AC Watts to DC amps instead of using 12 volts, use 10.. (There are very good reasons for this, and though it is a cheat,, At anything under 100 amps it comes dang close to accurate)

So 85 watts is 8.5 amps.. The voltage drop will cause the inverter to shut down.

Solution: You could put in an HD line direct to the battery or fuse panel and a 20 amp rated 12 volt outlet Or hard wire the Inverter to the fuse panel using like 8GA or bigger wire, (Well I used 12ga but it's only a 75 watt inverter and that's on my car so it's a short run.. about six or seven feet).

[enblethen]

You should have the negative of one battery going to the rig and the positive off the other battery going to the rig.

[2oldman]

For me to understand those pictures you'll have to take a shot from farther away. Either that or draw a wiring diagram.

[tfirma]

Thanks to everyone for their advice so far. Lots of ideas here and I have some troubleshooting to do. One thing - the 2 batteries are brand new AGM batteries. That's not to say it's impossible they could be the problem - but I'm hoping not! This morning I tested just the general battery power by running just the 12v appliances...and I was very satisfied... Looked like the battery levels dropped only slightly after running a number of things in the RV fora few hours. (I'm thinking the solar was doing it's job today - the sun was out a bit). The wiring / gauge seems to be an interesting theory. While Lance, the manufacturer, didn't tell me the gauge wiring they use - they do claim that I should definitely be able to use the 150W inverter with no trouble at all.

I also thought the suggestion of the 12V outlet being on the same circuit as the meters was interesting. (The meter panel is on the same wall as the outlet for which I've plugged in the inverter).

Before I wired the inverter directly to the batteries - I wanted to post pictures of the current battery configuration. Does this seem right? The batteries are wired to each other - which I'm pretty sure is correct from seeing online how to hook up 2 batteries. However, all of the other wiring is just coming off one battery - I thought seen in other diagrams online that other wiring should also be split between the two batteries? Or is it okay to be coming off of one battery, as you'll see in these pictures :

http://imgur.com/gallery/OOh6e/new

[pianotuna]

85 watts for the laptop equates to 8.5 amps @ 12 volts. The existing batteries are compromised in some way.

Check to see if the electrolyte is covering the plates. If it is not add just enough distilled water to do so then fully charge them--say for 168 hours at 13.2 volts.

After they are fully charged then disconnect them from the RV and do an equalization charge at 16 volts. Then check the specific gravity in each cell using a temperature compensated gauge.

[MEXICOWANDERER]

Hah! (When you learn why)

If you plug a regular cigarette lighter into one of your sockets and push it in you would have your answer sooner or later. My lighter sockets are wired with 10-gauge wire and protected with dedicated 15-amp breakers to minimize voltage drop. RV manufacturers may use 14-gauge wire or even 16 gauge and guess what it is SAE rated gauge not AWG.

Electrical wire prices make manufacturers shudder and bookkeepers woozy.

[BFL13]

Loaded voltage is lower than resting voltage. You are not sening battery 'drain' at the initial drop in voltage, but only after that while the load is running. Once the load is removed, battery voltage will bounce back. Not back to where it was, but to where it was minus the drain while the load was running.

With the thin wires to the 12v plug in, you will get more voltage drop under load, so you want to connect the inverter to the battery itself with fat wire for best results.

If the batteries are "weak" (old eg) they will show proper voltage resting but loaded voltage will drop way more than it would when the batts are "strong". You might be seeing some of that in there too.

[DrewE]

I agree with enblethen, you have wiring inadequacies more than anything. It may be something as simple as a poor ground connection at the battery, and cleaning it up would help things. Connecting your inverter directly to the battery would also work well, but be inconvenient. A more permanent solution with direct wire connections would be ideal.

Your meters are reading voltage, but not necessarily the voltage of the battery (this is particularly true for the one with the tank level meters). It's quite possible that they're also seeing the voltage drop from the inverter's current consumption. The battery voltage itself is probably rather higher than it suggests while under load.

You might also want to check the condition of your batteries if you have not done so yet.

[RJsfishin]

First thing I'd do is hard wire the inverter to the battery bank, or at least to the 12v distribution center. Then see if voltage stays up.
If the circuit that you have the inv on, happens to be the same one your meters are on, that mite explain it all.
Always hard wire the inverter,...just to get it out of the problem.

[enblethen]

Odds are the wire is too small to run the inverters.