Lucas Posted June 19, 2018 Share Posted June 19, 2018 Hi I am looking for some advice on fuses and solar panels. My aim is to install 2 x 100w solar panels that deliver max of 6 amps each. I have been using an online calculator to determine the size of the cable required and it recommends 6mm2 9AWG. The problem is I can't seem to find an inline fuse that has the same size cable to go at the battery end. I have only managed to get one that is 12 AWG. Will it be an issue using the 12 AWG inline fuse if it rated for up to 30amps ? Thanks in advanced. Link to comment Share on other sites More sharing options...
plwsm2000 Posted June 19, 2018 Share Posted June 19, 2018 Short answer is No. The reason why 6mm^2 cable is recommended is to minimise the voltage drop over the several metres of cable, more so than for its current handling capability. Provided you can reliably attach the wire to the fuse holder, it will be ok. Link to comment Share on other sites More sharing options...
aandncaravan Posted June 19, 2018 Share Posted June 19, 2018 You don't need fat cable if you design it correctly. Because the Voltage from the Solar Panel is typically 20v + you can afford minor voltage drop from there to the Solar Regulator. In theory you could use 1.5mm/16A cable, but that wouldn't be recommended. We suggest 2.5mm. However, once it comes out of the regulator it is regulated down to 12.8v - 14.4v where even fractions of a volt can have a big impact. So this part of the cable run is important. But the best advice suggests this is the place to keep the cable run really short, like less than 0.5m max. The best Solar regulator instructions actually stipulate this. I think Votronic suggest 0.6m max distance?. So the place to mount the Solar regulator is right next to the Motorhomes Power Distributor/Controller where the output from the Solar regulator will be supplied for distribution to the Habitation and Starter battery. If you look at the Sargent website, all their Solar cables to connect a regulator to the Sargent EC225, EC500, EC328, etc are all short for this reason. Because this cable run, if designed well, is short voltage drop on even 1.0mm (we recommend you stay with 2.5mm for mechanical strength) will be near zero. Many Solar 'Internet designs' assume the Regulator will be located up at the roof where the Solar Panel cable enters the Motorhome, hence the requirement for Fat cable from there to the Controller because the voltage can be as low as 13v in low sun. Obviously just a 0.5v drop takes this 13v down to 12.5v which is likely to be less than the battery voltage so zero charge will take place, even if the regulator has an amp or two to 'give'. When batteries charge fastest at 14.4v, even a 0.4v drop to 14v is going to slow charging down You can see that losing 2v from the 22v at the Solar panel end still results in 20v getting to the regulator. Obviously you don't want to lose 2v, but fractions are no real issue. . It is such a subtle thing yet has major impact. The Solar panel will still 'work', but you can see how the best will be twice as efficient as the worst installations, and we have seen some horrors. Using manufacturer specific cables usually saves a lot of time as they also pick up the feed to the Starter battery. I think the dearest Sargent Solar cable is about £14 and the cheapest £9, yet saves so much time. If you put a fuseholder in the cable where it comes in the roof, you have a way keeping the circuitry from 'being live' while you work and for isolating the Solar Panel for maintenance. When you have done yours, try and get yourself invited into other motorhomes to inspect their Solar solutions and look see how many do it so wrong. See here for more - http://www.aandncaravanservices.co.uk/solar-power.php Tip: If you have not bought your Solar Panel yet look at the Panel voltage (maybe 17v to 23v for a 100w panel?) the higher you can get the better, within reason. Clearly a 22v panel will be more efficient than a 17v at the start and end of day especially in Winter, when it's output can drop to 'near battery voltage'.. Link to comment Share on other sites More sharing options...
Lucas Posted June 19, 2018 Author Share Posted June 19, 2018 plwsm2000 - 2018-06-19 6:56 PM Short answer is No. The reason why 6mm^2 cable is recommended is to minimise the voltage drop over the several metres of cable, more so than for its current handling capability. Provided you can reliably attach the wire to the fuse holder, it will be ok. Thanks :-D Link to comment Share on other sites More sharing options...
Lucas Posted June 19, 2018 Author Share Posted June 19, 2018 Thanks for all the info aandncaravan. Unfortunately my sergeant system is an older version which does not have the option to plug a solar lead into the distribution board. I did check this with sargent. My panels are rated at 17v and 18v. The regulator recommends keeping the cable run to the battery within 2 meters, which is tricky. I had planed to install it in a wardrobe at the front of the van next to the distribution board and then run a cable back to the leisure battery which is located at the rear of van around 4 - 5 meters away. Or I could wire directly into the leisure battery terminals on the distribution board and use the existing cable to route the power back to the battery. Keeping the length of the cable from the regulator to the battery down to 0.5m would create issues in routing the cable down from the roof, through the floor and into the rear boot. I don't think it is impossible but no where near as easy as the alternative above. Link to comment Share on other sites More sharing options...
mikefitz Posted June 20, 2018 Share Posted June 20, 2018 The fuse near the battery needs to be 20 amp, use a maxi blade fuse and holder from 12v Planet, this holder can be ordered with connectors for 6mm² or 10mm² https://www.12voltplanet.co.uk/splashproof-maxi-blade-fuse-holder.html Mount the solar controller close to the battery as advised and use 6mm² cable , (10mm² would be even better). Anything over a meter or two is going to compromise the battery charging. Its better to have a long cable run from the panels to controller rather than a long run to the batteries. Most panels will be supplied with either 4mm² or 6mm² cable and MC4 connectors. Extend the cables to the controller using similar sized cables. Any small volt drop between the panels and controller is not a problem. There is no need for protection fuses between the panel and controller due to the characteristics of the panels. If your controller is a PWM type then connect the panels in parallel, if its a more expensive MPPT type, connecting the panels in series should be slightly more efficient. ( subject to the controller maximum input voltage). When installing the controller connect the battery cables first then the solar cables. Mike Link to comment Share on other sites More sharing options...
Lucas Posted July 6, 2018 Author Share Posted July 6, 2018 Thanks for the tips Mike. All wired up now and managed to get the controller just .5 meter away from the battery. Cheers :-D Link to comment Share on other sites More sharing options...
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