Member Since: 18 Jan 2017
Location: Lugano
Posts: 7
Split charge system in progress - a couple of questions
Hi there,
I'm in the process of fitting a split charge system in my Disco 4. I've already fitted the accessory battery (Optima Yellowtop) under the hood and did all the connections with the starter battery using the kit from simplysplitcharge (http://www.simplysplitcharge.co.uk/shop/viewitem.cgi?SCK101). Everything works fine, accessory battery is charging when the engine is on and stops a few minutes after the engine is cut off.
Now I'm in the process of running cables along the vehicle from the accessory battery to the boot where I will install a 12v socket for my National Luna weekender fridge/freezer, dual USB charging and Voltmeter, and a 500w inverter (220v socket in the boot).
I'm planning to run a 4 meter 20mm2 power cable from the accessory battery to the boot with a 60A fuse close to the battery, and (in teory) a 4 meter 20mm2 earth cable connected to the minus post of the accessory battery.
The 20mm2 cables will then reach a power distribution block that will split them up into 4 10mm2 cables for each block.
The 10mm2 cables will then be tied to the inverter, 12V socket, dual USB charger and Voltmeter.
What I'm planning to do is shown in the diagram below:
Click image to enlarge
In pink are power cables and green earth cables.
Now, the questions:
1. The diagram is correct?
2. I believe I have to install fuses in the boot too: do I place a single 60A fuse just in front of the power distribution block, or a 60A fuse in front of the inverter and 10A fuses in front of 12v, dual USB charger and Voltmeter?
3. Is it necessary to run a 20mm2 earthing cable from the accessory battery to the boot or is it easier (and still safe) to earth the inverter, 12v socket, dual USB charger and voltmeter directly to the vehicle frame?
BTW I'm doing the installation with the help of a professional, but it's the first time he's doing such a system, so I prefer to ask questions before doing something wrong...
13th Mar 2017 11:23 pm
Discovery-Dave
Member Since: 27 May 2015
Location: East Yorkshire
Posts: 157
Any particular reason you have selected a 60A fuse? (500W at 12V is 41.667A).
I would protect both the primary and secondary of the inverter. Therefore, a fault on the inverter would be detected and disconnected by a fuse, and also any faults downstream of the inverter shall be detected and disconnected - protecting the inverter.
The battery at the top appears to be missing the negative earth link.
I'm not an expert on DC (AC is my game) but earthing direct to the frame should be fine as long as the impedance back to the battery is low.
13th Mar 2017 11:51 pm
Eldainen
Member Since: 18 Jan 2017
Location: Lugano
Posts: 7
I've chosen the 60A fuse after searching a bit on the Internet, I'm no expert. Which one would you choose?
Yes I forgot the earthing links of the starter battery and the one of the durite relay, but they are present.
Thank you for your advice on protecting both primary and secondary feed to the inverter!
Since AC is your game, do you think that it is safe to put the inverter in the space behind the rear trim panel, between trim and bodywork, or do I need more ventilation?
Last edited by Eldainen on 14th Mar 2017 12:15 am. Edited 2 times in total
14th Mar 2017 12:05 am
Dan the Man
Member Since: 20 Mar 2014
Location: Glasgow
Posts: 215
Hi Eldainen,
You should install smaller, suitably sized fuses straight after the +ve power distribution block, with each fused for the likely draw and cable.
I see no point running -ve cable, it will be fine just earthing to a suitable point in the rear.
Take a look at this post, I found it very helpful:
http://www.disco3.co.uk/forum/topic128464.html
I fitted the sockets in a slightly different place though....
1981 Unimog U1300L (ex German Army vehicle
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14th Mar 2017 12:08 am
Eldainen
Member Since: 18 Jan 2017
Location: Lugano
Posts: 7
Wow, thank you for the link to your installation, seems to be just what I need!
I've yet to choose the placement of sockets in the boot, yours is a very nice solution!
14th Mar 2017 12:13 am
Discovery-Dave
Member Since: 27 May 2015
Location: East Yorkshire
Posts: 157
As long as the cables are rated for 60A, they should be fine. With the inverter only being 500W, I don't think the other 12V ancillaries will ever pull 20A. What is the rating of the fridge? And I presume the USB sockets will only ever pull a couple of Amp, so 10A fuses seem too high.
I'd probably protect the inverter at the power distribution block with a 40A. Is there already protection on the 220V side? Out of interest, what do you have in mind for the 220V?
Apologies for all the questions. Want to make sure I know the full picture before giving advice!
14th Mar 2017 12:23 am
Eldainen
Member Since: 18 Jan 2017
Location: Lugano
Posts: 7
The fridge should draw max 5 amps and is already protected with a 10A fuse, another one is not needed but I still may use the 12v with other applications (12v stove for exemple), that is why I want a 10A fuse there.
USB I think at max 2.5A so smaller fuse as you say. The same for the voltmeter I believe? Is it possible to use such a small fuse with a 10mm2 cable? After the fuse can I reduce the cable size?
I found the calculations I made to get to a 60A fuse for a 500 Watt inverter: 500watt/12volt than /0.8 (80% efficiency of the inverter) x 1.2 (to allow 20% surge). Don't know if this is right. Would be nice to go down to 40A because it will allow me to use 42A rated wires instead of the 70A 10mm2 wires.
The inverter is surge protected (AEG 500w inverter http://www.conrad.com/ce/en/product/513439...-USB-port) and I plan on using the 220v sockets of the inverter itself or the shortest extension cable possible. If I use a short cable do I need some extra protection?
The 220v will be used mainly to charge a laptop.
Finally, do you think that it is safe to put the inverter in the space behind the rear trim panel, between trim and bodywork, or do I need more ventilation?
14th Mar 2017 12:32 am
Discovery-Dave
Member Since: 27 May 2015
Location: East Yorkshire
Posts: 157
You will be able to reduce cable sizes if you reduce fuse sizes. Be mindful of grouping/de-rating factors though.
It is my understanding that in DC circuits there is no phase difference between current and voltage therefore the power factor is taken as 1.
Realistically, are you ever going to be pulling 500W continuously from the inverter? I'd always play it safe and use the smallest fuses possible (may be worth seeing what you are likely to be plugging in to see what consumption you are likely to use).
Regarding the extension lead, generally extension leads are already fused within the plug itself, and other appliances which you will be plugging in will be fused too.
14th Mar 2017 2:18 pm
Eldainen
Member Since: 18 Jan 2017
Location: Lugano
Posts: 7
Ok, I think I've got it. Going with the 40A, my laptop will never ever draw 500w (not even at startup), so a 60 amp fuse is too much.
Thank you for all your time and effort, this weekend I will probably be able to finish the work. I will post the results!
14th Mar 2017 7:44 pm
Andy Foster
Member Since: 27 Dec 2009
Location: Liverpool
Posts: 6551
This is mine. If you want I could make one for you and get it posted. PM for more details.
All switched and fused separately via a 12v fuse box D4 MY15 SE TECH
D3 gone but never forgotten.
14th Mar 2017 9:25 pm
Eldainen
Member Since: 18 Jan 2017
Location: Lugano
Posts: 7
It's a very nice setup, but I need to install an inverter behind that panel, so I prefer to find other locations. Thank you anyway!
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