Hello guys. I was just wondering if someone with knowledge of wiring, could take a look at my wiring diagram and let me know if it is sound.
I have taken onboard some suggestions from R.L. and have revised my diagram. Further help would be greatly appreciated. Thank you.
M:C Trailer Solar Build V5.0.1 22:09:26 09-38GMT.pdf (76.2 KB)
The battery-side cables of the MPP would be better at 10 mm². An RCD would be appropriate because of the double AC socket. However, this requires a neutral conductor to be created (connecting one 230 V pole to PE). This is not apparent from your plan. And an earth rod is then missing.
Hi R.L. Thank you for the reply.
I shall alter the wires from the MPPT 100/30 to the battery, to 10mm² as you suggest. My installation will be inside my touring/motorcycle trailer, so I have added an earth to chassis ground cable from the MPPT, Inverter, Consumer Unit and Socket. I thought that would be okay.
That is fine as long as all the components are fault-free. But if two components each have an undetected fault, it can be fatal: an extension lead is lying in a puddle and has a small crack in the insulation. One conductor then comes into contact with earth. And a work light has a short circuit between the other conductor and the metal casing. Current can then flow through the user’s body—from their feet, through their body, to their hand and the work light. Both faults may have been present for years without affecting functionality. If an RCD is installed, it would detect that less current is returning through one conductor than is being supplied through the other. The current flowing through the user’s body would account for the difference. The RCD would then disconnect both poles. It responds to a current difference of just 30 mA and trips within a few milliseconds. You can read more here.
Which inverter is being used? Victron or a no-name brand?
Please remove the forced potential bonding between the PV charge controller, inverter, negative busbar and chassis, and have the system rebuilt with the help of an electrician. There are differences between functional earth, protective earth and equipotential bonding; mistakes must not be made here!
The inverter GND should be connected in the distribution board, where the sockets should also be protected by an RCD (work for an electrician!). The installation will need to be tested afterwards anyway. The scope of the work and the type of RCD to be used depend on the type of inverter!
Thank you Karl-Keinz.
I have removed the obstacles you mentioned (I think)! I shall now upload a revised diagram.
Regards. Mike.
Hi Guys.
I have revised my diagram as per comments from you. Please take another look and let me know of any potential problems!
Regards. Mike.
M:C Trailer Solar Build V5.2 22:09:26 15-43 GMT.pdf (76.0 KB)
Do not install the red dotted cable on the lower battery! All currents must flow diagonally through the pair of batteries.
Are you familiar with Wiring Unlimited?
https://www.victronenergy.com/upload/documents/Wiring-Unlimited-EN.pdf
Thanks Karl-Heinz, that is a fantastic resource to give me a better understanding of things. Thank you. Mike.
Hi R.L. Okay. What I was thinking was that because the batteries are in Parallel, it might be better to send the solar electric to the start of the battery feed. Thank you for the warning, perhaps you could educate me a little more as to how the flow of electricity will flow through both my batteries and keep them both charged? That would be very helpful for me. Mike.
The image on the left shows the current being fed into both terminals of the lower battery. The lower battery draws a lot of current, while the current is channelled to the upper battery through additional cables (resistance). In the image on the right, the cable lengths for both terminals and both batteries are the same. The upper battery has a short red cable and a long black cable. The lower battery has a short black cable and a long red cable. The conditions are the same for both batteries. Therefore, the current divides into equal parts.
Thank you R.L. It’s nice to know that I got something right, I’ll remove the dotted possible route from the diagram tomorrow.
May I ask for your opinion of my cable sizes and breaker ratings. Are they safe in your opinion, or would you change anything for the better.
Regards. Mike.
To size the circuit breakers, you need the cable cross-sectional area (which in turn depends on the current), the installation method and the intended current load.
Sit down with an electrician! What kind of inverter do you have?
That looks good. The important thing is that the cables are not laid in thermal insulation or bundled together. Otherwise, the cross-section needs to be larger. They need to be able to dissipate heat. The cables between the battery, inverter and charge controller should be as short as possible. Otherwise, choose a larger cross-section here as well. Up to 125 A can flow to the inverter! Any voltage drop must be kept as low as possible. For example: the cables to and from the inverter are 5 m long in total and have a cross-section of 25 mm². At 25 A, you lose 0.018 V per metre with a 25 mm² cable. However, the cable is five times as long and the current is five times as high. That makes 25 × 0.018 V, or 0.45 V. The power loss is then approximately 57 W.
Hi R.L.
Thank you for the reply, I appreciate your help. Thankfully all my cables to each unit is very small, as I have mounted them onto a plywood board. The only long cables are from my batteries up to the board, the positive and negative 35mm² cables are around 35in (89cm) long. Would you consider this okay?
You really should get an electrician on your team!
Do not mount high-current equipment, e.g. distribution support points, on a combustible surface!
That’s OK.
But @Karl-Heinz’s point is important: I would screw two 12 mm Fermacell boards on top of each other onto the wood.
Please be aware that these 4 breakers are cheap Chinese knockoffs of Bussmann Series 285 surface-mount breakers, and are known to cause endless issues. Please strongly consider throwing these into the trash, and replacing them with reputable Bussmann, Mechanical Products, Egis, or Optifuse surface-mount breakers.
If you need to calculate cable cross-sections (among other things), you should take a look at the Victron Toolkit app.
