How many amps can I put through a 12v power socket? "Poor Man's Goal Zero"

[Martinjmpr]

Back in August I replaced the single 12v battery in our trailer (a T@B Clamshell) with a dual 6v golf cart battery setup. That required a new battery box and now I have an empty battery box sitting in my Pathfinder. I was going to just throw it out when I got an idea: Maybe I could get an inexpensive 12v car or marine/RV battery and make a kind of "poor man's Goal Zero" portable 12v power setup. :sombrero:
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The idea would be that I could use it to power 12v accessories when camping and it would not be tied into either my truck or the camper.
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I would set it up to charge off solar if necessary but if I wanted to charge it by plugging it into one of the 12v power sockets on my vehicle, what is the most amp/hour rating I could expect from the little 12v setup (while the truck is running, naturally.) 3 amps? 5 amps? Just trying to do the math here and assuming I get, say, a 75 AH battery and it gets 50% discharged, how many hours would I need plugged into a 12v socket to recharge it?
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I know folks here have figured this stuff out already (Dave in Denver I'm looking at you!)
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Thanks in advance! :ylsmoke:

 

[Scoutn79]

I imagine it is going to depend on the build of the particular socket you buy.
Look on Amazon, BluSea etc and see what the different ones are rated to carry.
Cig lighter sockets are fused at 20A so you should be able to get just under that with quality components and properly sized wiring...
See if the ratings are listed in intermittent or continuous current.

Darrell

 

[john61ct]

Ciggie sockets are a dangerous abortion, avoid like the plague.

5-6A max, and watch out for loose, sparking.

Blue Sea has a nice socket design that twist-locks with the matching plug, but will also accept standard ciggie plugs for smaller (<10A) loads.

Also the BMW/ Hella/ Merit/ Powerlet "Euro-style DIN" (ISO 4165) style is very robust.

Anderson plugs for high amps. If you standardize on one of the last two types, there are adapters for devices with ciggie plugs.

 

[nixid]

John are you suggesting replacing the cigerette adapter with another plug only? Or does he need to run a seperate wire from the battery?

 

[Martinjmpr]

I see what you guys are saying, but using a different style of plug would defeat the whole purpose of the exercise since the idea is to have a portable power source that I can take anywhere and that will work with any vehicle.
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And while 12v power sockets may not be "ideal", they are universal, whereas other types of power connectors are not.
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So my next question would be: Is there a 12v battery charger out there that's not total crap? Or, how difficult would it be to make one? I use 120vAC battery tenders (float chargers) on my motorcycles when I'm at home, I'm wondering if there is a 12v version out there, something that has a voltage regulator built in that will prevent the battery from overcharging?

 

[IAm_Not_Lost]

I wouldn't call it a poor man's goal zero, I would call it "not paying a fortune for something you can essentially build for a third of the price".

The sky is the limit on what you can easily add to a box and a battery. Throw a fuse box on the underside of lid so that you can - easily and safely - run a few different connections from the battery, like a cigarette lighter plug, a USB type port, an anderson plug, exc. If you want a DC to DC type charger then the Optimate on Amazon get's good reviews.

To answer your original question, every glass fuse I have pulled out of cigarette lighter plugs (the male end portion) always has a 10amp fuse in it. Now, does that mean you can't have better quality components and a higher fuse rating? No, but that seems to be a pretty standard amp rating for cigarette sockets.

 

[rayra]

I've been satisfied with the connectors I got thru powerwerx.com, there are no-name ones on amazon for 1/2 as much. Or you can pay 2x as much for something from BlueSea or the other marine providers.
Still haven't finalized my power connections. Next up is my folding solar panel kit integration. Might add an MC4 bulkhead connection (common connector standard with solar) but I really want to re-wire that panel kit setup with Anderson connectors, so I can set it up a couple different ways and locations. Or even add a cig lighter port plug as a pigtail. So the panel kit can be used on someone else's vehicle if needed.
I want ALL the connection options. The recent hurricane disasters and prepper discussions are showing a real need for folks to be able to charge their smartphones. Seems society is becoming overwhelmingly dependent on them, even besides in a post-disaster environment. The standard 12v receptacle is certainly the defacto standard and a small sack of adapters gets you just about anything you want in the 12V / 5V USB world.
I set up my power expansions for camping / glamping / 'ExPo' / HAM radio support / disaster prep / etc. So I wanted all the common ports / flavors of juice. This way I can power or recharge just about anybody's tech gear.

 

[Martinjmpr]

I wouldn't call it a poor man's goal zero, I would call it "not paying a fortune for something you can essentially build for a third of the price".

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Well, yes, there's that, but also it is really just an excercise in "what can I do with this battery box I don't need anymore?" :sombrero:
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The sky is the limit on what you can easily add to a box and a battery. Throw a fuse box on the underside of lid so that you can - easily and safely - run a few different connections from the battery, like a cigarette lighter plug, a USB type port, an anderson plug, exc. If you want a DC to DC type charger then the Optimate on Amazon get's good reviews.

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Yeah, so all the talk about using non-standard connectors I think misses the point. Because what I'm looking for is something I can use on ANY vehicle, and while I know they are not ideal, the 12v "cigar lighter" socket is the de facto standard.
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What got me started with all this was looking at my DD which is a 2002 Nissan Pathfinder (R50.) Now anyone familiar with the R50 knows it is not a super-rugged "off road" vehicle, what with its unibody construction and McPherson strut front suspension (and yes, I know there are folks here on ExPo who have done some pretty amazing R50 builds.)
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But what I started to think of was "what if I wanted to take an extended back-country trip in the Pathy?" The one thing that would worry me would be that it likely would not have adequate battery power to run the fridge, and I've really come to like the fridge for convenience. Obviously, I could (a) sink a bunch of time, money and effort into upgrading the battery power in the Pathy or (b) go "old school" and just use an ice chest or cooler, but then I though "what if I could make an inexpensive portable 12v power source, enough to run the fridge, and take that instead?"
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The other nice thing about this option is that it would mean that I could use it with ANY vehicle. So if I decide to get rid of the Pathy, or if I decide to take some other vehicle, I don't have to spend a lot of time upgrading the charging system, I can just pick up the pieces and throw them into whatever vehicle I'm using at the time. So that's the reason I'm looking for something that can be charged up easily from a standard 12v power socket (and that's the reason I called it the "poor man's Goal Zero.")
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At this point I have no interest in putting in an inverter, since I can't think of anything that I would need 120vAC power for. Basically I'd want somthing that could run the fridge and maybe charge a cell phone or computer. Seems to me that not having an inverter makes it much, much simpler. Really I just need the battery, an output and some way to charge the battery, that's it. If I could fit the whole thing into a small box or ammo can or something that would even be better.
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So who has built something like this? Any thoughts or tips? BTW I'm not committed to using the old battery box, that was just the item that spurred this whole idea.

 

[Martinjmpr]

Still haven't finalized my power connections. Next up is my folding solar panel kit integration. Might add an MC4 bulkhead connection (common connector standard with solar) but I really want to re-wire that panel kit setup with Anderson connectors, so I can set it up a couple different ways and locations. Or even add a cig lighter port plug as a pigtail. So the panel kit can be used on someone else's vehicle if needed.

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Yes, exactly. I envision something like this but much smaller and simpler, with no inverter. Something that could either be charged up by a standard 12v power socket (hence my original question) or a solar panel. Preferably something that doesn't weigh much more than the battery itself and is self contained.

 

[Martinjmpr]

Another reason...

OK, it's funny, this whole thing started just as an idle intellectual exercise but now it's really got me to thinking that there's another reason for me to be seeking a portable 12v power source like this.
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Last year I posted up here about my project of putting a dual battery setup on my current "ExPo" vehicle (really my "trailer tug"), a 2004 Suburban. It was a very enlightening experience, I learned a lot and got a lot of great help from the folks here, especially Dave (Dave in Denver) who greatly assisted me in making power cables and in helping me understand how the system should work.
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But all in all, I probably "invested" close to $500 in that setup, and several weekends worth of work - probably 50 - 60 hours total. It works great and I love having the extra power.
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The thing is, I know my Suburban won't last forever. It's got some body rust on it already, and some on the frame (courtesy of years in Wisconsin.) It's got 166,000 miles on it and although a new transmission was put in at 150,000 miles, I have to face up to the fact that sooner or later it's going to get to a point where it's going to be more expensive and time consuming to keep it than to get rid of it in favor of something newer.
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And if I do get a newer vehicle, I have to ask myself: Am I willing to invest the same amount of time and money that I did on the Suburban, in order to get that extra battery capacity? If I'm honest with myself, the answer is "No, I am not willing to do that."
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Not because I don't like having a dual battery, but rather because I don't know that the benefit would be worth the money and effort. This is especially true if I can come up with some other kind of auxiliary power source that will enable me to run the accessories I need (primarily the fridge) WITHOUT a full-on dual battery system.
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The advantages of a portable system are many: I can swap between vehicles, and I can upgrade individual parts as needed. Since I'll be building this from scratch, I'm not limited (as I was with the Suburban) to a battery that was of the correct physical dimensions to fit into the space under the hood.
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EDITED TO ADD: It just occurred to me that what I'm trying to build is more akin to an ArkPak than a Goal Zero. Honestly I don't need the inverter of the ArkPak but the other stuff looks very well made. Might have to consider whether shelling out $350 would be worth it (I know I'd still have to bring my own battery but a Group 31 AGM with 115 AH of power runs about $130.) If ArkPak made a stripped down version of their box, with no inverter, for say $250 or so, it would be very tempting to just go with that.

 

[Martinjmpr]

Fwiw,
If you want to build a 'universal' battery pack.
Consider including a long cable with big roachclips what can directly connect to a battery.
If it comes down to it, Most cars have enough space to run a cable thru a gap around its hood or trunk & then in thru a window or whatever.
Aside from cars with enclosed batteries. In a pinch, It will guarantee easy ability to gain high capacity charging from just about any car regardless the state of its cigar sockets.

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Yes, this is another thought that occurred to me. Basically a set of jumper cables to send power directly from battery to battery. Could only do it when stopped, though.
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I see 6a being the max current I can expect through a 12v socket. I would actually be OK with 6a, basically it would be like having it connected to a 100w solar panel (which puts out between 5 - 8 amps.)
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See, here's my thought: Assuming I start off with a fully charged 115ah 12v Group 31 AGM battery like this one:
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https://www.apexbattery.com/trojan-...MI0pGLkoqw1gIVhEZeCh1pDwcoEAQYAiABEgJtBvD_BwE
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(I'd go with AGM so as to avoid any outgassing problems with a FLA battery), run a 12v power cord from the battery (through a fuse, of course!) to a 12v socket. The fridge is in the truck too, but here's the thing - while I'm driving down the road, the fridge is plugged into the vehicle's 12v power socket, NOT the aux battery box. So by the time I get to the campsite the battery should still have its full charge.
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Then once I get to the campsite, I shut off the vehicle, take the plug out of the vehicle 12v socket and plug it into the "power box." The fridge runs all night (and as much of the next day as I'm not moving) off of the power box. Unless it's unusually hot, power draw should be on the order of 3 - 5 ah. That means if it runs off the power box for 12 hours, it should consume, let's say, at most 48ah (12 hrs x 4ah), drawing the 115ah battery down to ~ 60%, more or less.
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Next day, start the vehicle, plug the fridge into the vehicle, and plug the power box into the 12v socket. If I can get 6ah out of the socket, and if I drive 8 hours, it should be fully charged by the time I get to my destination (6ah x 8 hrs of driving = 48ah.)
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So is there anything wrong with this plan? Anything I haven't taken into consideration? Let me have it, I'm looking to learn here. :ylsmoke:

 

[Martinjmpr]

a drawing...

Here is a very basic rendition of what I'm looking to do. I'll apologize in advance for not using standard electrical symbology, I'm trying to do this off of powerpoint and I don't have any kind of background in engineering (which is why I'm trying to keep it simple):
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Would this work? I'm leaving out niceties like "smart" charge controllers, fans, inverters, etc. Basically just a battery-in-a-box that I can swap from vehicle to vehicle and still run my fridge, charge my phone, etc.
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Some dumb questions:
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1. Assuming that the battery has been used and is at less than 100%, let's say it's at 80% with a charge of about 12.5v, and I plug a 12v plug into the socket on the top left, then plug the other end into a car's 12v power plug, while the engine is running, wouldn't that charge the battery? If the engine is running, I should be seeing around 14v at the 12v power source on the car, so wouldn't that power flow back into the battery and charge it?
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2. If it is set up as above, with the 12v power plug "downstream" from the ammeter, would the ammeter still work? Or is the ammeter only able to measure current "one way", i.e. from the battery to the 12v port on the box?
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3. Is a 10a fuse adequate for power coming directly off of the battery? If not, what amperage should the fuse be? Is there a better way to acheive this without creating something that is overly complex?
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What gauge wire should I use? The distances involved will be small - on the order of 1' or less for the longest wire. I'm thinking 12g should work OK without being so stiff as to be unmanageable?
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The 12v power socket would likely be something like this. It is advertised as being a "25a" socket. Obviously if this is the case I'd go with at least a 30a fuse.
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https://www.amazon.com/Waterproof-C...sr=8-1&keywords=high+current+12v+power+socket
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The in-line voltmeter/ammeter would be something like this:
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https://www.amazon.com/Ninth-City-D...5789151&sr=8-7&keywords=12v+voltmeter+ammeter

 

[southpier]

"roachclips"

ha ha ha

 

[Martinjmpr]

Whats shown will work great. KISS !
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Most Chinasium digital ammeters are not bidirectional. One would need two of them in order to monitor both charging and discharge current. Further, your battery would require separate charging terminals if one is using two of those meters.
But (to complicate further for electro-newbee) some of those cheap meters can share the same shunt if using two meters...
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If you wanted only to monitor appliance loads, and dont care what charging current is, charging would have to be input 'upstream' of the meter.
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Btw, I never tried connecting one of those cheapies backwards. I dunno if it would harm anything or just not display...
Also, note that meter you shown, does not list its max ampacity. Based on the picture, I might think its max is less than 10amps.

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All good points, thanks for the input. :26_7_2:
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So I'm thinking of a variation on the above: I actually would rather measure input amperage rather than load amperage, so maybe a 2nd charging circuit, using an SAE power connecter, which could then go to either the 12v power socket OR to a solar panel (my solar panel already uses the SAE connector to connect to the trailer battery.) I'd then put the ammeter/voltmeter in line with the charge circuit so I would have the ability to know (a) the current voltage of the battery (which should be a good indicator of the relative state of charge) and (b) the input amperage so I would have an idea of how many amps I'm getting from my power source.
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Makes sense?

 

[Heavyopp]

You said a few posts back -- " NO inverter, can't think of anything I would need 120 AC for"

I have a box, Built it for family car camping to run the ARB fridge and not tax the vehicle battery -- I did put an inverter in

I'm in NJ -- A few years back we had Hurricane Sandy roll thru -- House was out of power for 11 days along with most of central Jersey

That box with inverter was a lifesaver, Just for Hot water -- I ran a generator from 9am to 9pm so whole house was fine during the day

Nighttime use was the box, Cable tv was up so ran TV and the hot water heater

I have natural gas hot water but the thing won't run without a small amount of 120 volt AC -- Needed to run the circuit board and the induction fan and light the burner

Just a thought on why to put in an inverter....