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  1. #1
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    Default Help with DIY 2nd battery box

    Please could someone with more experience review my drawing below and tell me if I have things correctly connected? Also could you please comment of what size cables to use between everything? Any help will be appreciated.


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    Default Re: Help with DIY 2nd battery box

    What amps do you intend pulling from the outputs. This will determine the size

    16 mm sq for crank to WRND and to aux. Recommend the wire to be double insulated multi wire core.

    6mm sq to fuse box, as above.

    Have a look for a calculator on the web for 12 V dc systems to assist.
    Stranger

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  3. #3
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    Default Re: Help with DIY 2nd battery box

    Thanks for the reply, I plan on running a Snowmaster 80lt fridge/freezer off of the Harris plug and a compressor which states 45A on the side of it. Those should be the biggest current items I intend to use.

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    Default Re: Help with DIY 2nd battery box

    This, it will open a whole new world to you - enjoy the adventure:
    https://www.4x4community.co.za/forum...ry-for-camping

    And a fuses to each and every pos. cable, for each battery, as close as possible to the battery.
    Last edited by hatjohan; 2021/01/15 at 12:08 PM.



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  6. #5
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    Default Re: Help with DIY 2nd battery box

    This is very very similar to my setup, but with a few exceptions and maybe some ideas you might want to consider. I'm not saying you must do it this way, I'm just saying what I did.

    1. My system is completely isolated from my crank battery, as I personally didn't want any connections into my vehicle's electrics. So, my PV panels ONLY charge the aux battery.

    2. I have a 40A DC circuit breaker that isolates my panels, so I can "switch the panels off" if I so desire.

    3. Similarly, I have a 40A DC circuit breaker that can isolate my battery. If both battery and PV circuit breakers are off, I have zero power into the system (up until the "entry" side of the breaker).

    4. I also have a hella (for my fridge), two cigarette lighter and one (dual) USB outputs, but I run them all off the same circuit breaker, seeing as in total they're unlikely to draw more than 5-10 amps.

    5. I have one more separate circuit, also with it's own separate 50A DC breaker for my compressor (also rated at 45A max). Since I didn't want to cut my compressor cables to for a Brad Harrison, I run those wires to two plumbing copper pipe lugs, onto which I can attach the crocodile clips. Another reason for not wanting to cut the cable is that there may be a time when I (or someone else) may need to use my compressor off a car battery. If it has a BH connector, what then?

    6. I learned (thanks Fluffy and Stranger!) to use DC circuit breakers, and not AC ones.

    7. Each of the 4 circuits is protected by both the breakers AND a fuse on each. I used strip fuses (they're cheap as chips) mounted onto bolts, and have a plastic cover over them so they're not exposed. I agree with Hatjohan, mount them as close to the power source as possible ; although a circuit is a circuit and none of the cables are earthed to any part of the vehicle.

    8. Although it's a bit bulky, I housed my circuit breakers in a standard "electrical box". Bulky, but neat. I mounted everything onto some spare wood I had lying around, and I think the whole installation looks fairly neat (but a bit bulky, as I mentioned).


    Happy to post pics and a circuit diagram if it will help...
    Rob Kirk

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  8. #6
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    Default Re: Help with DIY 2nd battery box

    Quote Originally Posted by Ama-newbie View Post
    This is very very similar to my setup, but with a few exceptions and maybe some ideas you might want to consider. I'm not saying you must do it this way, I'm just saying what I did.

    1. My system is completely isolated from my crank battery, as I personally didn't want any connections into my vehicle's electrics. So, my PV panels ONLY charge the aux battery.

    2. I have a 40A DC circuit breaker that isolates my panels, so I can "switch the panels off" if I so desire.

    3. Similarly, I have a 40A DC circuit breaker that can isolate my battery. If both battery and PV circuit breakers are off, I have zero power into the system (up until the "entry" side of the breaker).

    4. I also have a hella (for my fridge), two cigarette lighter and one (dual) USB outputs, but I run them all off the same circuit breaker, seeing as in total they're unlikely to draw more than 5-10 amps.

    5. I have one more separate circuit, also with it's own separate 50A DC breaker for my compressor (also rated at 45A max). Since I didn't want to cut my compressor cables to for a Brad Harrison, I run those wires to two plumbing copper pipe lugs, onto which I can attach the crocodile clips. Another reason for not wanting to cut the cable is that there may be a time when I (or someone else) may need to use my compressor off a car battery. If it has a BH connector, what then?

    6. I learned (thanks Fluffy and Stranger!) to use DC circuit breakers, and not AC ones.

    7. Each of the 4 circuits is protected by both the breakers AND a fuse on each. I used strip fuses (they're cheap as chips) mounted onto bolts, and have a plastic cover over them so they're not exposed. I agree with Hatjohan, mount them as close to the power source as possible ; although a circuit is a circuit and none of the cables are earthed to any part of the vehicle.

    8. Although it's a bit bulky, I housed my circuit breakers in a standard "electrical box". Bulky, but neat. I mounted everything onto some spare wood I had lying around, and I think the whole installation looks fairly neat (but a bit bulky, as I mentioned).


    Happy to post pics and a circuit diagram if it will help...
    Rob, I would like to see this please, the next time we meet up. I would prefer to keep the auxiliary battery separate from the vehicle battery and I made a small version in December 2019 as a model for a larger version.

    Being an edjit, I tend to learn from doing hence the working mini-mock up mentioned above and would like to see a larger one in the flesh.

    (No inappropriate innuendo was used in this post)
    Estee = S T = Sean Towlson

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  9. #7
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    Default Re: Help with DIY 2nd battery box

    Quote Originally Posted by Estee View Post
    Rob, I would like to see this please, the next time we meet up. I would prefer to keep the auxiliary battery separate from the vehicle battery and I made a small version in December 2019 as a model for a larger version.

    Being an edjit, I tend to learn from doing hence the working mini-mock up mentioned above and would like to see a larger one in the flesh.

    (No inappropriate innuendo was used in this post)
    Thanks, Sean, I'll show you mine if you show me yours (NO innuendo intended either).

    I'd love someone to cast a critical eye over my setup, and suggest improvements. I also tend to to prototype, prototype and prototype and then just keep the final prototype as production. I write code that way too, just don't tell my boss (although I think he suspects this is the case anyway)...
    Rob Kirk

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  11. #8
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    Default Re: Help with DIY 2nd battery box

    Click image for larger version. 

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    Should give some idea of the end result... note the "copper pipe lugs" for the compressor....
    Last edited by Ama-newbie; 2021/01/15 at 01:06 PM.
    Rob Kirk

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  13. #9
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    Default Re: Help with DIY 2nd battery box

    Thanks Rob. Here is my mock up

    Its powered by a small solar panel and I use it for charging small things and lights



    Click image for larger version. 

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    Estee = S T = Sean Towlson

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  14. #10
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    Default Re: Help with DIY 2nd battery box

    Cool!

    As with mine, can't tell too much from a photo. We can do a "show and tell" next time we meet...
    Rob Kirk

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  16. #11
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    Default Re: Help with DIY 2nd battery box

    Quote Originally Posted by Ama-newbie View Post
    This is very very similar to my setup, but with a few exceptions and maybe some ideas you might want to consider. I'm not saying you must do it this way, I'm just saying what I did.

    1. My system is completely isolated from my crank battery, as I personally didn't want any connections into my vehicle's electrics. So, my PV panels ONLY charge the aux battery.

    2. I have a 40A DC circuit breaker that isolates my panels, so I can "switch the panels off" if I so desire.

    3. Similarly, I have a 40A DC circuit breaker that can isolate my battery. If both battery and PV circuit breakers are off, I have zero power into the system (up until the "entry" side of the breaker).

    4. I also have a hella (for my fridge), two cigarette lighter and one (dual) USB outputs, but I run them all off the same circuit breaker, seeing as in total they're unlikely to draw more than 5-10 amps.

    5. I have one more separate circuit, also with it's own separate 50A DC breaker for my compressor (also rated at 45A max). Since I didn't want to cut my compressor cables to for a Brad Harrison, I run those wires to two plumbing copper pipe lugs, onto which I can attach the crocodile clips. Another reason for not wanting to cut the cable is that there may be a time when I (or someone else) may need to use my compressor off a car battery. If it has a BH connector, what then?

    6. I learned (thanks Fluffy and Stranger!) to use DC circuit breakers, and not AC ones.

    7. Each of the 4 circuits is protected by both the breakers AND a fuse on each. I used strip fuses (they're cheap as chips) mounted onto bolts, and have a plastic cover over them so they're not exposed. I agree with Hatjohan, mount them as close to the power source as possible ; although a circuit is a circuit and none of the cables are earthed to any part of the vehicle.

    8. Although it's a bit bulky, I housed my circuit breakers in a standard "electrical box". Bulky, but neat. I mounted everything onto some spare wood I had lying around, and I think the whole installation looks fairly neat (but a bit bulky, as I mentioned).


    Happy to post pics and a circuit diagram if it will help...
    Very useful info, thank you. Please post a circuit diagram if you can, Iím interested to see your individual circuits. Thanks

  17. #12
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    Default Re: Help with DIY 2nd battery box

    Quote Originally Posted by Ranger.RSA View Post
    Very useful info, thank you. Please post a circuit diagram if you can, Iím interested to see your individual circuits. Thanks
    Will do tomorrow with pleasure. Iím sitting with load shedding at the moment, contemplating the meaning of life...
    Rob Kirk

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  18. #13
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    Default Re: Help with DIY 2nd battery box

    Quote Originally Posted by Ama-newbie View Post
    Click image for larger version. 

Name:	electrical_bakkie.png 
Views:	341 
Size:	764.7 KB 
ID:	602359

    Should give some idea of the end result... note the "copper pipe lugs" for the compressor....
    I snipped my compressor power cable and put anderson plugs on both sides. That way I can connect with the standard clips to a battery, or split the cable and plug into anderson source as well.
    2009 Toyota Fortuner Epic V6

  19. #14
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    Default Re: Help with DIY 2nd battery box

    Quote Originally Posted by faanie View Post
    I snipped my compressor power cable and put anderson plugs on both sides. That way I can connect with the standard clips to a battery, or split the cable and plug into anderson source as well.
    Brilliant idea, thank you, going to do exactly that.
    Francois

  20. #15
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    Default Re: Help with DIY 2nd battery box

    Quote Originally Posted by faanie View Post
    I snipped my compressor power cable and put anderson plugs on both sides. That way I can connect with the standard clips to a battery, or split the cable and plug into anderson source as well.
    I did consider that, but I have an (irrational?) aversion to cutting cables from original if I don't have to - something about voiding warranties (although that's moot now as the compressor is about 2 years old). I also randomly swing between spendthrift and cheapskate and didn't want to buy another two BH plugs...

    I'll get on to that schematic now. Feeling a tad tender - thanks loadshedding, for giving me nothing better to do...
    Rob Kirk

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  21. #16
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    Default Re: Help with DIY 2nd battery box

    Click image for larger version. 

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    So, typed out my response, and then loadshedding hit AGAIN as I was about to press <send>

    So, here goes again. The schematic is just that, a schematic. The actual wiring is slightly different, but follows the schematic in principle. The cables to the battery I think are 16sqmm, all others are 6sqmm. All breakers and fuses are 40A except for the compressor ones, those are 50A.

    I have include a photo of the connector I made for the panels. I chose to wire them in series as their maximum output voltage is only slightly above the minimum input voltage for the Victron to charge a fairly flat battery. Downside is that any shade from a tree or whatever renders them pretty useless. The upside is that in low light conditions (early morning, late afternoon or cloudy day) and they still put some charge into the battery.

    My panels (2 x 160W) might be overkill, but they charged the battery after a night's usage in about 2 hours, from 08:00 - 10:00 on a hazy day.

    Happy to answer any other questions. I'd welcome constructive feedback from anyone actually qualified in this field; I'm not. So use my suggestions at your own peril!
    Rob Kirk

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  23. #17
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    Default Re: Help with DIY 2nd battery box

    Quote Originally Posted by Ranger.RSA View Post
    Please could someone with more experience review my drawing below and tell me if I have things correctly connected? Also could you please comment of what size cables to use between everything? Any help will be appreciated.

    Looking at your drawing. Negative wire, no fuse needed. Junction block will be fine. Connecting solar panels in serie, has the potential , if one panel mal functions, the whole system is down. This also means, that both panels must be connected at all times.
    Fuses needed for both batteries, as close as possible to the battery. Switches not necessary between plugs and fusebox. Unless there will be permanent cables connected.
    Pieter Kemp.
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  24. #18
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    Default Re: Help with DIY 2nd battery box

    So I've been giving this "fuse as close to the battery" some more thought (and in one of my posts I agreed).

    In a normal car situation, where the entire metal bodywork is the common negative, this makes 100% sense as you don't want a long piece of non-fused electrical cable attached to the positive terminal flapping around. So you fuse as close to the battery as possible. This to me makes total sense.

    However, in the circuits discussed above this is not the case, as each element of the circuit is composed (or should be composed) of insulated electrical cable. So why does it matter where the fuse goes; it should be able to be placed anywhere in the circuit, and if the fuse blows no current will flow.

    To take this a step further, science in high school told me that electrical current is the flow of electrons in a conductor. Using this assumption, the current actually flows from the negative terminal towards the positive. So, if you want to place a fuse "as close to the battery as possible" in a circuit composed entirely of insulated cable, the fuse should actually be close to the negative terminal, not the positive. Same for circuit breakers.

    Thoughts please?
    Rob Kirk

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  25. #19
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    Default Re: Help with DIY 2nd battery box

    Think of the event the Positive cable somehow gets damaged, even a little. If this shorts with a Negative like the vehicle body/chassis etc. - instant full current flow !! Now if this happens in between the fuse an the battery terminal the fuse would offer zero protection. To minimise this risk is to have a cable protection fuse right on the batt terminal
    Donít blame yourself over past mistakes. Itís like driving down the N1 while looking in the rear view mirror only.

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  27. #20
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    Default Re: Help with DIY 2nd battery box

    I fully agree with you in the ďnormal car scenarioĒ, where the whole steel body of the car is the negative, and thought I made that clear in my post

    I was then referring to the scenario where the entire circuit was made up of insulated cables (with properly insulated connectors - maybe I should have added that). In that case I donít believe the position of the fuse makes any difference...
    Rob Kirk

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