Using safe and correct wiring and fuses for portable 12v power source

Thread Starter

Kevislost

Joined Jan 2, 2017
4
Hello all,

The name is Kevin. I am an all around diy type of person. Most of my background is in finish carpenty and my college education is in Ecology. If you need more info than that about me just ask.

I have been working on a little project that is best described as a portable 12v power bank primarily for use with small electronics. (Several children with phones & tablets, a wife who cannot live without a social media, etc). Here is the lowdown:

> 36amp hour (2 x 18ah) SLA-AGM deep cycle batteries by Mighty Max
> 20Amp max JVR TL49 PWMsolar charge controller
> 20watt 1.15 amp 12v solar panel (to be expanded to 4 panels that will be folded up and stored when not in use)
> 12v accessory outlet
> 12v/ 5v USBports 1x 1.1a and 1x 2.1a (future plans to add another of these on for multiple tablets/phones)
>400watt inverter
> SAE battery connector for 1amp trickle/ maintenance charger.
> All this is neatly contained inside a small, portable, locking plastic crate with an o-ring to prevent moisture doing damage.
>future LED 12v work light.

Now, for the most part, I tried to research and size things appropriately. Really, this is more of a "fun" project than anything serious. But as an emergency preparedness tool (72hour kit kinda thing, not long term), or entertainment (small projector) for an out door movie night, this thing has posibilities.

Where I am needing a little guidance is in wiring and safety.

The exterior wiring is taken care of. I oversized the solar panel wiring to 10awg (PV, outdoor uv resistant etc). Basically that leaves plenty of room for expanding the solar panels to about 4.60 amps if I stick with my current panel (1.15amps) and get 3 more. Or more with bigger panels (100w x 2). So now moving inside the box.

I started with simply making sure I had an inline fuse on each line:
>5amp on the solar panel line before and after the charge controler to the battery
>5amp on usb accessory
>2amp from the SAE power conector for the AC trickle charger.
>15amp for the 12 accessory socket.
> and the inverter has its own fuse in the back of the box.
>CB185-100 -Bussman 100 Amp Type III Circuit Breaker (this acts as a main switch for all loads on the batteries, simply push the little red button and it kills all loads)

*side note* The 100amp DC breaker is very overkill and really serves no purpose except as an on/off switch at this time. It was intended as protection for a 1000/1500watt inverter to prevent overloading the system. However, it wasnt until later that I learned that the most I could get out of the 2 little batteries was going to be around 18amps. Not 100. So the inverter got downgraded and the 400watt will eventually be wired more directly to the batteries via the breaker. Currently it can be plugged in to outlet for use on the 15amp fuse.

Now you may think I have this well in hand... but honestly there is a difference between knowing what I am doing and doing it RIGHT. All of these are inline fuses and frankly that makes a bit of a mess. Especially if I am going to add any extra accesory outlets or USB charging ports. I bought a 6 way blade fuse box that can be mounted for easy access and replacement specifically for accessories (the fuses before and after the charge controller will remain the same).

Feel free to critique and or berate my ignorance and unsafe practices.

Fuses are not necessarily to protect the loads or batteries they are to protect the WIRE. So what type of wire should I be using? (Yes, this is a question)

I have the batteries jumpered together parallel with 4awg wire (thick strands) to prevent resistance from high draw. But I simply bought stuff from the hardware store and it was stiff and problematic getting them to play nice. After some research I found that specific battery wire should have been used. So that will be on my "to be replaced" list.

The two inline fuses for the charge controller are on very flexible 10awg wire (possibly silicone wire?) which was much easier to connect/crimp/route. The negative wire for the same connections was just plain 10awg stranded that (again) was very stiff and obviously the wrong type of wire for my application and gave me trouble (hardware store).

The accessory stuff are wired in with what came in the boxes. I think 23gauge on the USB and 18gauge on the accessory plug (switched for 12gauge that I found lying around). I plan on getting new wire, sized to the loads and the connections, to redirect into the blade fuse box.

Can someone explain what kind of wire I should be getting for this use? I have found a lot of different types/classifications of wire such as:

>hook up
>primary
>silicone
>marine grade
>THHN/THWN (this is what I grabbed from the hardware store, obviously wrong)
Etc

Is there some types of stranded wire that will give me better conductivity than others?

One last item. What about voltage use/ variability? While I don't plan to start a car with this, should voltage drops due to usage be a concern? If I have a phone and tablet plugged in charging and someone decides to use the inverter for something, should I be adding something to filter/condition/prevent voltage irregularities and damage to whatever else is hooked up?

So, fuses? Wiring? Voltage variations? Any other helpful advice or should I put my self in a hospital ward for missing obvious safety concerns.

I can load up pics tomorrow after work and I figure this forum all out.

Thanks for your patience and taking time to actualy read this badly writen novel (thats what happens when you want details!).

Kevin
 

Colin55

Joined Aug 27, 2015
519
The problem with 12v is this: You have no lee-way for voltage drops.
That's why the minimum low voltage distribution in the old-days was 36v (approx)
As soon as you try to take 5 amps and have one ohm of resistance in the wiring, you lose 5v and nothing works because you only have 7v available at the end of the run.
A car battery is 40A-hr and it doesn't last long when being used. It drops to 10v
You need a lot more "donkey cells"
And obviously you need wiring that is twice the recommended thickness because the wiring normally runs 100v or so and you don't mind losing 10v.
 

tranzz4md

Joined Apr 10, 2015
310
THHN, as you now realize, isn't the right stuff for your application. Colin is right on with his reply and you need to do the calc's to really determine the correct wire size. It's all readily available online and in smartphone apps.

Use very fine stranded wire, and use "rubber" style insulation. Most single conductor wire/cable uses vinyl and polyethylene based compounds for insulation, which are typically a bit stiffer than you'd like, and very stiff at lower temperatures.

I've been a commercial/industrial electrician for 37 years now, and know well what's readily available in the USA, (your language and expressions strike me as US) and the small quantity you need doesn't make it easy to get your hands on stuff, especially with nearly all component level electronics purchasing now being online, so you can't feel it before buying some.

You may find it easiest to buy a suitable length of "SO" type cable, and stripping it down to the individual conductors. That will give you the physical flexibility you seek, and your use of insulation colors is nobody else's business!
 

Thread Starter

Kevislost

Joined Jan 2, 2017
4
Yes I am relatively aware of the problem of line usage and resistance. That was actually why I oversized my battery jumpers and the leads from the batterys to the loads. 4awg jumpers and 4 awg to the bussbar and breaker switch then each load has its own wires from the buss bars. Well over my current needs. I really dont expect to draw more than a few amps at any one time. I just want to prevent problems if say someone plugs in the inverter to draw while phones are plugged in. (Kids have a habit of saying "lets try this....!")

I was thinking maybe adding capacitors or some other nifty idea to make sure that nothing surges and creates electronic paperweights.

Almost all my wiring is oversized for the reasons of resistance. Using the batteries as a base of the system (not the loads) I probably dont need more than 6 or 8 awg wires. In fact my PV lines dont really need to be thicker than 12gauge but I made them 10 for insurance. Now if the batteries were 100ah and meant to power appliances.... that is another story.
 

Thread Starter

Kevislost

Joined Jan 2, 2017
4
As for getting some SO line...I was considering that. I just didn't want to have any problems with possible insufficient insulation. In fact I saw some 10/4 in a nice rubber wire that was the tail end of a real at the hardware store and was very flexible. I was considering that but decided to ask people who know first.
 

Thread Starter

Kevislost

Joined Jan 2, 2017
4
The problem with 12v is this: You have no lee-way for voltage drops.
That's why the minimum low voltage distribution in the old-days was 36v (approx)...
I think I understand now what you are saying about 36v distribution and voltage drops. I suppose theoretically I could wire the batteries in series for 24v at 18ah. But then I would need to get some sort of transformer for each accessory that reduced the voltage from 24>12v. That would take care of the distribution problem you pointed out. Unfortunately this is a very small system contained in a small box and I don't think I could pull that off.

However, if I ever decide to do an RV, house system for off grid, or a bigger less portable system, then that is something I will keep in mind. In fact that would make complete sense. I would probably go for 48v.

As for car batteries, they may have the CCA to get 100 amps (for about 10 seconds) but they are much to big to be portable. I can only wish I could get that many amps out of my little power pack. The reality is that running appliances is best done off a gas type generator if that is what is needed.

Thank you for that advice though. If I could fit a few extra cells in to cover the drops then I would
 

tranzz4md

Joined Apr 10, 2015
310
The small dimensions of your system is to your advantage!

Quickly looking in a handbook, I see the resistance of #10 AWG as 0.9989 ohms/1000 ft. So, if your connections and terminations are good, and your conductors circuit length is 10ft, you'll only have 1/100th of an ohm of conductor resistance, which is pretty good even at 5V on your USB stuff (which can handle the least voltage drop, but draws a pretty tiny current). Do the math with 400 VA and 12 V though, and you can see the effects.
 
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