12v for the Minimalist Weekender

[DoctahDeane]

I know you are not supposed to go below 50% capacity with these deep cycle batteries. So, what number am I watching out for?

12 volts. But you may notice as soon as you turn something on, the voltage drops. To actually monitor the battery, you need to wait at least thirty minutes after any load has been put on the battery and then take a look at it. It's called resting voltage. An hour is better.

Nice looking setup. You need to go camp. So do we.



Tony

Thanks a lot. OK, that's great. I understand. Yes, very ready to camp although this polar vortex is hanging around. I'm not convinced about the plumbing setup. I inherited a pump and there's a holding tank underneath. Just feel like a lot of stuff. Thinking of a simple water jug and maybe leave sink in place as a simple drain to a waste jug. Just need to get out and experiment. Made the mistake of reading some posts on the forum last night and of course, now I'm interested in shocks. I've learned a lot and now I could imagine revisiting my incomplete build and doing that right. It's wider (5' wide) and now I really see how everything fits. I already have the profiles cut and platform done, undercoated and attached but I like your book suggestion of building off the trailer. Geez, I guess I'm hooked. Thanks for all the assistance.

[DoctahDeane]

This is a simplified voltage SOC chart. Do realize these voltages are the battery at rest, meaning left alone for 24hrs.



Now this is the meter 'I' use. https://www.amazon.com/MICTUNING-6-5-100V-Digital-Voltmeter-Multimeter/dp/B01JOUZELG/ref=sr_1_6?crid=3DX1WM6C9NAP7&keywords=12v+meter+display&qid=1570278958&sprefix=12v+meter%2Caps%2C199&sr=8-6 I have one on the solar panel showing incoming and one on the battery showing outgoing. What I like about these is they use a external shunt (not a big fan of the intervals yet..) and reads cumulative Whr's.



So here I show 12.46v (battery voltage) / .22a being used (or 220ma) / 2.7 watts of power / 379Wh of energy used since last reset. Sorry but didn't take a picture of the one on the panel soI could show you the comparison. Main number I look at is the Wh #. In this case if higher than 379, my batteries haven't reduced at all.
Also need to say that in this picture the panel is not hooked up, otherwise that voltage reading would be in the mid/high 13's..(incoming voltage or panel voltage)

As another said: 'You' need to figure 'your' use and work towards a battery that will work for the amount of time you require. Adding solar just adds to duration. The chart I showed you is a combination of 4 folks (myself included) testing different appliances and coming up with a comparable number between all of us. It's as close as we could get and a decent basis to work from.

For you, you may not even have Ghost draw, especially if what you plan to use has no stand-by mode. I have a lot of Ghost draw due to the appliances I have. That's where doing the audit is important, it tells you 'your' usage.

Is there some wiring trick to this device to get Power and Current readings? I can see the Voltage level (12.61 at the moment) and Energy but the other readings are zero and I've switched the wires around to see if I had 'em backwards but nothing changed. The instructions are not super clear. Did you come upon any instructions that made the wiring clear? I'd like to see the impact when I switch on any of the 12v devices in the cabin or galley, ideally.

[tony.latham]

I can see the Voltage level (12.61 at the moment) and Energy but the other readings are zero

Turn your fan on. My LEDs suck so little power I can't even measure them.

Tony

[DoctahDeane]

I can see the Voltage level (12.61 at the moment) and Energy but the other readings are zero

Turn your fan on. My LEDs suck so little power I can't even measure them.

Tony

Excellent suggestion, Tony, thank you. No dice though. But, as it turned out the ground wire running back from the shunt was going simply to ground and not to the negative post on the fusebox. My confusion about terminology (load and shunt, especially). Anyhow, it works now. That was driving me nuts. Just wanted it to be right. So now, mattress just arrived from FedEx. Add some loom to cover the reading light wires and then it's on to simple plumbing set up (ha ha) but can easily hit the road as is. If you happen to read this just want to confirm that as I monitor battery charge, I don't want to go below 12 so, I'm thinking that once I get down in the 12.10-12.15 range, I should be seriously considering recharge. Sound right?

[DoctahDeane]

As I wait for my solar panel suitcase to arrive (first one arrived damaged), I've been getting the wiring ready. I noticed that on my battery monitor that there's a drain - not bad - since I topped it off about 2 weeks ago, using the charger and extension cord to garage. After top off, it read about 13.05 volts as I recall and that lines up fine with manufacturers guidelines and suggestions. When I just glanced at it, it's at 12.86. I have not used any electrical in the trailer this whole past two weeks - no lights, no fan, no water pump - nada. I understand that just sitting idle, a battery will drain. I will watch and keep notes but just curious about this issue and any sort of phantom power that might be lurking in my overall set up. I suppose the charger (Noco Genius 3500) might draw a bit just sitting? One of my USB ports has a blue light that must always be on but there's a rubberized cover so you don't actually see until you uncover it. Also, I suppose the USB port inside the cabin while not illuminated, might have a little draw? The "current" reading is 0.04 and when I turn on the galley overhead light in the hatch, that jumps to 0.23 then back to 0.04 when I turn it off so I think the 0.04 reading suggests that something(s) are constantly drawing a bit? Like I said no worry, just wanting to understand.

[tony.latham]

The "current" reading is 0.04 ...

Which equates to an amp/day of course. I suspect it's the USB ports but the only way to know is to pull them apart and disconnect them.



Tony

[DoctahDeane]

That's where I am headed next and thanks for the math lesson, too. so that 0.04 x 24 = roughly one Ah per day as you say, which if it just sat there without being used, implies that for this 100Ah battery and safety considerations, maybe could go roughly 50 days until the need for a full recharge? Seems that way, math-wise. As far as locating the source, I guess I can disconnect items one by one at the fuse box and look at the meter each time. I put all the running lights on the bottom row of the fusebox and all the trailer stuff on the top row (fusebox is sideways), so process of elimination ought to be pretty easy. I suspect the USD or the 12v power port...does your Current reading register anything when idle?

[MtnDon]

Before tearing into any parts I would first simply disconnect the battery and see if the voltage value drops or remains constant over a week with the system like that. Then if there was a small similar drop I would put it down to battery self discharge. That is one reason I have a disconnect on the battery "out" wires. I can turn off any use but can leave the solar charger input connected. Any connected electronics may have a small draw on the battery.

[tony.latham]

maybe could go roughly 50 days until the need for a full recharge?

First of all.. when MtnDon steps in, I listen.

Secondly, you are getting that draw --or at least your meter thinks so. So you have both that parasitic draw and natural battery drain. So wouldn't bet on fifty days.

If you look at depth of discharge and battery life charts, I don't think allowing your battery to dip that far is an ideal situation. Perhaps Don or Bill will chime in here. Those guys go a bit farther than me and my depth of knowledge on how to keep my phone charged.

Tony

[DoctahDeane]

Thanks, guys. I appreciate it. I'm not trying to go 50 days or get down to some low level. I was just trying to see if my math understanding was roughly correct. I really should take a course in basic electricity.

MtnDon: thanks, I really like this idea. To me, this would be like establishing a baseline - then I'd know roughly what to expect from the battery itself. I would expect that once I'm using the trailer regularly (soon, please) that a rhythm of sorts will be established and it'll all be straightforward. Still, if there's something pulling unnecessarily, seems like it would be good to know. Cool! Another experiment. I'll report back.

[DoctahDeane]

I just played around a bit and have isolated 75% of the drain (0.03) to the USB ports. I suspect the other 0.01 is probably the 12v power port. Interesting - our dependence on phones affects this too! It's a PITA to push back the mattress and open up the electrical box each time so obviously, some sort of switch that kills power from the fusebox is the way to go. I could have this anywhere, really. Any suggestions? I assume the switch has to interrupt the + post on the fusebox, somehow?

[tony.latham]

Any suggestions?

You might replace the USB outlets with ones that don't have a light.

https://www.amazon.com/gp/product/B07CJW3ZRP/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

Tony

[DoctahDeane]

Any suggestions?

You might replace the USB outlets with ones that don't have a light.

https://www.amazon.com/gp/product/B07CJW3ZRP/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

Tony

I considered that, Tony, but interestingly, the one in the cabin that does NOT have a light is the 0.02 draw and the one in the galley WITH the light is s 0.01 draw. Weird, right?

[Tom&Shelly]

Any suggestions?

You might replace the USB outlets with ones that don't have a light.

https://www.amazon.com/gp/product/B07CJW3ZRP/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

Tony

I considered that, Tony, but interestingly, the one in the cabin that does NOT have a light is the 0.02 draw and the one in the galley WITH the light is s 0.01 draw. Weird, right?

Hi DoctahDeane,

That's because the USB ports have little DC to DC converters built in them. They take the 12 volts in and make 5 volts to charge cell phones, etc. The converters have a little parasitic draw that is evidently about the same as the draw for the indicator LEDs.

My wife doesn't like LED lights in the cabin while she is trying to sleep, so I broke into the USB boxes and cut an LED lead. Still works fine without the LED (green in those cases)



I experimented with these, with white rectangular boxes (works with standard switch plates), and with some black round USB ports and found the latter produce an annoying hum on nearby radios. May or may not matter to you.

Incidentally, reading through the thread, your understanding of basic electricity appears to be pretty sound.

Tom (retired EE)

[tony.latham]

The converters have a little parasitic draw that is evidently about the same as the draw for the indicator LEDs.

That explains that.

Incidentally, reading through the thread, your understanding of basic electricity appears to be pretty sound.

I was thinking the same thing. You've evolved.

Tony