Boondocking power options

[charliem]

What Charlie said. I don't think any 12V battery is a true deep cycle battery with heavy plates and more room above and below the plates for electrolyte and sulfate buildup. See
http://www.pbase.com/mainecruising/deep_cycle_battery. Everywhere you see "boat", read it as "RV".

David

[font size="3"]Excellent, but wordy, article. I hope more RVers will read, understand, and heed it. Thanks for the reference.[/font]

[fasteddieb]

Quick data points...

Current draw with light blue wire attached to ground lug: 1.22A

Current draw with light blue wire disconnected from ground lug: about .84A but hunts around a bit.

I suppose every little bit helps.

Found an appropriate switch and will probably work on wire and terminals and mounting the switch later today.

[charliem]

[quote timestamp="1461085785" source="/post/20676/thread" author="@fasteddieb"]Quick data points...

Current draw with light blue wire attached to ground lug: 1.22A

Current draw with light blue wire disconnected from ground lug: about .84A but hunts around a bit.

I suppose every little bit helps.

Found an appropriate switch and will probably work on wire and terminals and mounting the switch later today.[/quote][font size="3"]Yes, every little bit helps when dry camping. What instrument were you using to measure the two currents? Clamp on, if so what range, or in circuit DMM?[/font]

[fasteddieb]

In-line between the negative battery terminal and the two ring terminals that normally attach to it.

I used this $6 Multimeter that Harbor Freight periodically offers for free. It has a 10A range.

http://www.harborfreight.com/7-function-digital-multimeter-90899.html

[charliem]

[quote timestamp="1461088165" source="/post/20679/thread" author="@fasteddieb"]In-line between the negative battery terminal and the two ring terminals that normally attach to it.

I used this $6 Multimeter that Harbor Freight periodically offers for free. It has a 10A range.

[a href="http://www.harborfreight.com/7-function-digital-multimeter-90899.html"]http://www.harborfreight.com/7-function-digital-multimeter-90899.html[/a][/quote][font size="3"]OK. Just wondered since the delta should be very close to 0.5 Amps. I'm not sure about the accuracy of the HF meter. Most such meters are inaccurate at the low end of a high current range. Also I see the HF meter is traceable to the National Bureau of Standards. In fact, they just threw it in the Dumpster last week (old joke) .

I also wonder what the second ring terminal on the battery negative is. Mine only has one to the negative. The positive now has two since I added a power tongue jack. I assume you had shore power disconnected. If not the readings could be anything.[/font]

[fasteddieb]

Both my terminals have two wires and ring terminals going to them  - I've never traced them to see where they go. I did check and there's zero effective resistance between the negative terminal and the frame when hooked up.

I did shave shore power turned off throughout.

Did this this afternoon:


I was going to drill a hole in that aluminum pane for the toggle switch, but may just wedge it in below the panel and secure it with RTV or equivalent. On the fairly rare occasion we boondock for more than one night, easy enough to remove the external cover and switch the heater wire off.

[fasteddieb]

[quote source="/post/20081/thread" author="@charliem" timestamp="1459450318"][font size="3"]Interesting idea, batteries on the rear. The factory bumper should be fine. The batteries, though heavier, will not impose the torque load that cantilevered bicycles do. You'll have to make the rack and really tie them down because they'll get more whiplash back there than on the tongue. David's correct on wire size though I'd go with #8 or even #6 copper. Easily obtained at home improvement stores. Geometry being what it is you gain almost a pound for every pound you take off the tongue and you gain another 1/2 pound for every pound you hang on the bumper. Put 2 golfers on the back, wire it with heavy wire, and you're ready to go off the grid. Add solar someday and we won't hear from you for months.  8-)     

Camp on!
[/font][/quote]
My current (wild) plan is to ultimately end up with 2 golfers on the back.

But for now, I can wire my existing 12v spare on the rear bumper as a "proof of concept".

Rough plan is a 2GA cable or braided cable from the negative terminal to the frame. Then run a 2GA copper cable from the positive terminal, under the trailer to the front. Install a marine battery switch there to select between batteries in use. Not as efficient as running it to the converter, but I don't expect much drop from the 2GA wire.

I assume some sort of heavy duty fuse or breaker at the battery is a good idea. If so, what would be suggested for that application?

Idle hands, and all that!

[david]

Yes, a fuse near the battery is a good idea even though I don't think there is one on the front battery. The general rule is the fuse is sized to protect the wire, which in your case #2 is good for 200 amps which is more than you will ever see except for a fault. But your wiring scheme has it going forward to the front battery which is only wired with 10 gauge to the converter and the power distribution panel, so use a 30 amp fuse.

I appreciate that you want to wire to the forward battery so you can then use a spdt switch up there to select which battery is supplying the trailer. I would prefer wiring the new battery directly to the converter/DC panel and switch each battery separately.

Finally I assume that the existing DC system uses the frame as a ground, but where does it tie in. At the converter, at the forward battery, or ?

Electricity is complex isn't it? Charlie will probably have better ideas.

David

[charliem]

[font size="3"]Boy, we're getting deep into it here. It's time for Eddie, Charlie and David to get out on the road!

Eddie, your plan sounds OK. #2 is probably overkill; #4 would suffice. I think the OEM battery and converter are wired with #6 or #8, but too hard to tell. Either way the 30A fuse will work fine, but a 40A would be OK too. I might prefer the 40 in case you charge sometime with jumpers to the TV. Normal use a on board charging will be fine with 30A. An A,B (either) battery switch will be fine, just remember to switch it to the unused battery when charging. With the chassis as return and #4 or #2 connecting them you could even use an A,B,A+B (either or both) with very little loss of life (the battery's). That would also increase your usable capacity slightly, thanks to Mr. Peukert.

The chassis is grounded to the 12V system. I think the connection is to a bus behind the converter, but not sure.

BTW your fridge heater switch brings new meaning to the term Floating Switch    .
[/font]

[fasteddieb]

Thanks for the rapid responses...

1) I thought of 2GA because of prior voiced concerns about voltage drop over a 20+ foot run. If 4GA is sufficient, it's likely to be cheaper and easier to route. Certainly all the stock wires are rather on the thin side, anyway.

2) This battery switch gets good reviews:

http://www.amazon.com/Blue-Sea-Systems-Selector-Battery/dp/B000K2MCR2/ref=sr_1_1?ie=UTF8&qid=1461186669&sr=8-1&keywords=marine+battery+selector+switch

So, placing it on "1+2" while driving would charge both batteries safely? Even if they had different ratings or states of charge?  I had thought to choose one or the other depending on state of charge.

3) Switch is not floating any more!

[charliem]

1) I thought of 2GA because of prior voiced concerns about voltage drop over a 20+ foot run. If 4GA is sufficient, it's likely to be cheaper and easier to route. Certainly all the stock wires are rather on the thin side, anyway.

2) This battery switch gets good reviews:

[a href="http://www.amazon.com/Blue-Sea-Systems-Selector-Battery/dp/B000K2MCR2/ref=sr_1_1?ie=UTF8&qid=1461186669&sr=8-1&keywords=marine+battery+selector+switch"]http://www.amazon.com/Blue-Sea-Systems-Selector-Battery/dp/B000K2MCR2/ref=sr_1_1?ie=UTF8&qid=1461186669&sr=8-1&keywords=marine+battery+selector+switch[/a]

So, placing it on "1+2" while driving would charge both batteries safely? Even if they had different ratings or states of charge?  I had thought to choose one or the other depending on state of charge.

3) Switch is not floating any more!

[font size="3"]1) 20Ft jumper cables equals 40Ft of cable. Two way loss. 4AWG is fine for you with the frame return. Charging while driving is primarily limited by the OEM wiring in TV and TT. I carry 20Ft 4AWG copper cables.

2) The Blue Sea switch is excellent. Leave it in 1+2 when charging or using the batteries. Only reason to use one or the other separately is for diagnostics or failure. The charge/discharge should be very near equal. Separate them and charge separately at home every now and then to assure complete charge. You'll probably do more damage by trying to keep track of which separate battery to use and recharge.

3) Fridge switch looks good if it stays.[/font]

[whoofit]

Yes, a fuse near the battery is a good idea even though I don't think there is one on the front battery. The general rule is the fuse is sized to protect the wire, which in your case #2 is good for 200 amps which is more than you will ever see except for a fault. But your wiring scheme has it going forward to the front battery which is only wired with 10 gauge to the converter and the power distribution panel, so use a 30 amp fuse.

I appreciate that you want to wire to the forward battery so you can then use a spdt switch up there to select which battery is supplying the trailer. I would prefer wiring the new battery directly to the converter/DC panel and switch each battery separately.

Finally I assume that the existing DC system uses the frame as a ground, but where does it tie in. At the converter, at the forward battery, or ?

Electricity is complex isn't it? Charlie will probably have better ideas.

David

It is not simply a frame return.

Negative battery lead proceeds to frame directly, at that node to another 10AWG and that runs to converter area where it ties into the ground block, again connected to the floor. So there is more than just the frame and floor as the return. There is a return 10AWG conductor as well as the 10AWG positive lead.

When I rewired to 6AWG I did both wires. Was concerned if I had a ground loop going on or not. In the end I kept the original 10AWG and added 6AWG giving me 5AWG or better because of the frame return.

[fasteddieb]

I received the battery select switch and its pretty impressive. Claimed to be waterproof and spray proof.

Physically mounted it just now:






Will work on the wiring over the next week, once I get the wire and the fuse block I ordered. While I'm at it I may fuse the front battery as well.

Once its all hooked up, if the switch is on "1+2", both batteries will in effect be in parallel. In that state, they would both equalize, correct? And they would charge together, whether it was from shore power or the car or a charger - solar or otherwise - hooked to one or the other, correct?

I ask, because I had really intended to "manage" the batteries, always with one or the other selected, but charliem questioned the necessity.

[charliem]

[font size="3"]Eddie,

They will not charge/discharge exactly equally, but they'll be close enough. If you trace the wiring to and from each battery to the converter you'll see there are some differences. The front battery has a run of #6 in the both positive and negative back to the converter. The rear battery shares that positive run but adds the longer run of #4 you ran back. However the rear battery has essentially no wire to the negative since, I think, you wired directly to the frame. I think you can assume the converter is connected directly to the frame in the center of the trailer. So the difference is the resistance of the long #4 positive vs the shorter #6 in the negative of the front battery. I think we're splitting hairs. Go with it. If you really want to be perfect, and you have time and beers available, you can physically switch the battery pairs from time to time.      I wouldn't. I think you'll do more harm by trying to use and switch them manually.

Camp on!
[/font]

[fasteddieb]

Progress report...

Yesterday I picked up 30' of 4GA copper power cable and some terminals. Ran the wire under the trailer to the back.

Today got the rear battery hooked up, with a 30A "maxi" fuse:



So, I've just about doubled my total battery capacity, and actually reduced tongue weight a hair. Of course, picked up a little total weight. but I can live with that.