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Relays in electrical systems: worth or not?

Discussion in 'Maserati' started by Froggie, Apr 22, 2020.

  1. Froggie

    Froggie Karting

    Sep 27, 2017
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    There are quite often questions raised regarding the protection of parts and components of the electrical system in classic Maserati's.
    At that period of time, not all of the high current consuming components such as starter, headlamps, fans, fuel pumps, electrical motors, etc. were directly fed through relays.
    Hence high currents flowing in parts of the electrical wiring and switches... leading to degradation over time and early failures.

    The electrical diagrams, when included in the use and maintenance manuals, are not very easy to read and may contain errors.
    Here for example, the one of a late Maserati Indy which looks to me incomplete:

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    For example, according to this diagram, my 1974 Indy has relays to feed the cooling fans, horn, headlamps but there are no relays for the fuel pumps (components 102 and 103, on the bottom left) and there are no indications about possible relays for electrical motors of e.g. the radio antenna or electrical windows.

    On my car, relays were installed to feed new electronic Facet fuel pumps when replacing the old (non working) fuel pumps, following advice provided by Ivan:

    https://www.ferrarichat.com/forum/threads/4-9l-fuel-starvation-facit-fuel-pump-failure.408000/page-6

    Although I understand it depends much of the design and dimensioning of the electrical cystem of each car, I would be curious to know your view, in general, of additional relays worth to be added to feed directly electrical components in order to ensure the right voltage and current, and to avoid overloading the overall electrical system (and/or what electrical components would not deserve a relay):
    each fan?
    each electrical motor?
    radio system?
    interior lamps?
    ...
     
  2. MK1044

    MK1044 F1 World Champ
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    Nov 6, 2011
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    Generally, as you note, a relay is used where the controlled device has a high current draw, so as to isolate the device from the dashboard controls. I don't see any point in adding additional relays and hence complexity except in the case of a high current draw device.

    To that point: I recall studying the electrical diagram for the Khamsin and finding a few errors. Whether they were errors in the drawing or in the actual build of the car is unknown.
     
  3. thecarnut

    thecarnut Formula 3

    Apr 22, 2006
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    Working on the electrical system of a car that is now around 50 years old can be tricky. The best weapon is to use a an amp meter to take measurements and determine which circuits are placing the largest loads. Also to consider is how much time that circuits puts the load. For example, power windows only place the load in the short while they are being operated while radiator fans and the interior can place the load for a long time.

    Adding relays is not always the best solution and I personally dislike adding "stuff" unless absolutely necessary. For example, for interior lights the best solution is to replace them with LEDs. They draw much less current, produce little heat and last a long time.

    On my Ghibli the radiator fans were pulling less air than similar fans on an Indy. I was told by a Maserati mechanic that as the fans get older they are less efficient. This sounded as a possibility but before I bought new fans I needed to make certain. First, I measured the amount of air being pulled by the fans through the radiator using the same air flow tool used to synchronize carburetors. I then connected a fully charged battery directly to the fans and took the same air flow measurements. To my surprise there was a 50% increase in air flow! I then connected the amp meter and the current draw was the same as the Indy. The problem were not the fans but the wiring to the fans as the circuits already had two factory installed relays (one for each fan). I ran 12 gauge wires to the factory relays and now the engine runs much cooler and everything looks stock.

    A typical problem area where a relay many times helps is the interior ventilation fan. Measure the amount of air flowing out of the vents when the fan is in the fastest setting. Now take the same measurement by connecting a fully charged battery directly to the fan motor. If there is a significant difference then adding a relay, which feeds directly from the battery when in the fast setting, is the best solution and one I've added to many of my cars.

    Bottom line is there is no one size fits all solution, you need to look at each circuit to determine the best solution, and sometimes the best solution is to clean the contacts and leave them alone.

    Ivan
     
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  4. Froggie

    Froggie Karting

    Sep 27, 2017
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    Thanl you Ivan, very useful
     
  5. Froggie

    Froggie Karting

    Sep 27, 2017
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    Ivan, one additional question if I may.
    I see several remarks from yours on the absence of relays to protect the low beam wirings/switches, while the high beams are usually (except maybe for the Ghibli) activated through relays:

    I understand that the current drawn by low beams is of the same order than for high beams.
    Plus, usually the low beams are used more often and during longer times than high beams.
    Would you know why such an odd wiring choice by the factory?
     
  6. thecarnut

    thecarnut Formula 3

    Apr 22, 2006
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    High beams use at least twice more current than low beams. Remember that when the high beams are on all four Ghibli headlights are on. On a car like the Bora, with only two headlights, the high beam will have four filaments on while the low beam only has two. Still, putting a relay on the low beam would have been the smart thing to do as it will significantly reduce the amount of current the stalk switch will have to handle. I guess they wanted to keep things simple, plus they never planned for the cars to last 50 years.

    Ivan
     
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