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| custom90 Member Since: 21 Jan 2010 Location: South West, England. Posts: 20441  
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You may want a switch on your Amp RMT12V+ blue turn on, as with it it when ignition is on you’ll have the Amp on all the time when not even in use.
Unless you have multiple Amps where the Amp switching load exceeds 150mA, you may as well have that switched from the HU output RMT+. If it is multiple Amps with higher load, then ignition live manually switched would be better. Which allows for more switching load. The latter here being better if you want to or are likely to have an expansive system where you might want extras as the RMT12V+ Blue is useful also for other things such as Amp fans, electronics etc that you want only on with the Amps. Various switching gives loads of opportunities, but for a basic switching id use the HU RMT12V. Bearings in mind I wouldn’t exceed 250mA load on it, which is really its capacity on most systems and it also needs fusing nearest the HU. So a 200mA quick blow glass 20mm fuse might be ideal, and then downstream from that right next to that an inline 1A max diode. With its only purpose really to prevent fly back voltage from the Amp switching or anything else downstream which could come back up into the HU’s PCB and components. Relay switching coils can be culprit for flyback voltage, which is why I prefer relays with diodes in-built. The bigger HD relays cause more possible flyback voltage from the coil and many don’t have in-built diodes but you can add an external one for dissipation of it in parallel externally. Also bear in mind headroom for extra load, as you can get something may need adding unplanned and over spec the fuse boxes for extra circuits in case extra is needed which is likely. There are quite a lot of options to be had, but as I said with a HU RMT, be sure not to overload that as it can fry your HU if you did, it’s perfectly safe up to about 250mA load but beyond that no. It also needs fusing no more than that also, but as that load isn’t that high for anything more than one or two Amps it’s best to have a manually switched fuses, ignition live supply instead where the load is not a factor that is a limit. I personally think the less load on a HU the better, keep it for clean low load RCA signal only and for visuals and audio settings. The flyback voltage with relays is in regards the coil, not the input and output of the load switch. I like to have an in-line diode and a parallel diode, which is blocking upstream and dissipating at the relay. The smaller relays you can get them in-built often to about 40A but above, you can add externally. You don’t really want voltage spikes going into the LR loom or auxiliary fuse boxes where electronics are present if you can help it. Ferrite clips and Mylar foil shield can also be excellent for improving FM / DAB signal, and cutting down EMI / EMF. I’ve done it and it does work, you don’t need any fancy shielding wraps either you can make some with aluminium foil tapes and wrapping with Mylar. TDK ferrite clips are good on power supplies, but most generic ones are just as good I think. Well worth fitting, and also good quality convoluted tubing. If anyone happens to replace their DAB Aerial upon removal, I’d thoroughly recommend entirely shielding the cable, joints and connection boxes. Leaving only the HU and exterior Aerial / Antenna. It WILL improve your radio signal in particular DAB, and it’s not the easiest or fastest job to get that cable out so if you replace it I would recommend doing the shelling on top of any shielding that may be in the cable. When I mention Mylar shielding, it’s multilayer plasticised aluminium foil of which you can cheaply buy as emergency foil blanket from Amazon or eBay etc, you can buy that and cut it into stripe make sleeves with it and with double sided tape or aluminium foil tape. Just don’t wrap anything that may produce a lot of heat such as HU or Amp or where any ventilation is needed though it can be strategically placed instead. I was pleasantly surprised how effective ferrite clips and Mylar shied is, and will even cut down significantly high EMI unwanted noise from LED light bars or USB PSU’s. Perhaps not 100% but a good 90%. This turned into a long post.   $W33T $0U7H3RN $UG4R
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9th Feb 2024 4:00pm |
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