isolation transformer for electronics???

bob311

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    Hey guys,
    is any one out there running a isolation transformer or power filter for their electronics? I put an oscilloscope on my power leads and was surprised to see the amount of distortion everywhere on on the system. I'm just trying to get the cleanest power source possible for the fish finder. my set up is (2) stating batteries in parallel and two deep cycle in parallel wired to a perko switch. All of my accessories, (radio, stereo, bait pump, masc pump, bilge pump, lights, fish finder) are on the deep cycle batteries in parallel. I have (1) fused terminal block to handle all of the loads and the fish finder is wired directly to the batteries (see diagram below)
    1670264462103.png
     
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    bob311

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    I thought i was going to have good clean power by coming directly off of a battery furthest from the alternator but once the engine starts i could see the alternator "noise" on every power lead. Turning on each accessory only made it worse which is why i was thinking of putting in a small isolation transformer or noise filter.
     
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    ShadowX

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    I thought i was going to have good clean power by coming directly off of a battery furthest from the alternator but once the engine starts i could see the alternator "noise" on every power lead. Turning on each accessory only made it worse which is why i was thinking of putting in a small isolation transformer or noise filter.

    You can't use a normal isolation transformer in general because you need an AC waveform in order to switch the magnetic flux and couple power through. The DC needs to be converted to an AC signal, go through the isolation transformer and then converted back to a DC in order to work. Because of that, these packaged DC to DC isolated converters are more expensive.

    You have to know how much current you plan to run through a DC to DC converter or isolators. They are not exactly cheap either for the DC-DC converters. This one below is only a 50W unit (12V at 4.17A) and its $150.

    1670288097055.png


    What you really need to do is find out what type of filtering you want. Most noise are high frequency noise from the alternator at 500 Hz or higher depending on the RPM. A low pass filter design that allows DC to go through but filters out high frequency noise seems like the better option from a cost point of view. Some of the simpler filters are just capacitors while others have toroidal inductors (sometimes called ferrite beads) in series to provide additional filtering. These inductors acts as RF chokes to suppress high frequency AC signals.

    You can find these low pass filters relatively cheap on Ebay and many other places at around $15 for a 20A board. Personally, I haven't had the need to use one, so I haven't seen how well it filters. You may need to use a DSO (digital storage oscilloscope) to compare the waveform in the input to the output to see how well it cleans the signal. Most modern DSO has FFT (fast Fourier transform) to convert the signal to the frequency domain to be able to see the noise spurs at various frequencies. A spectrum analyzer or network analyzer would be better, but most of us can't afford that.

    If you do plan to use an open design like this, you will need waterproof it with conformal coating and house it in some sort of plastic box to prevent moisture from getting in. I would also stake all the heavy parts like inductor and capacitors to prevent them from moving and causing the solder joints to fail in a high vibration environment. You can pot it with epoxy or use E6000/B7000 glue. Pot first, let it cure completely and then apply conformal coat. My conformal coat of choice is MG chemicals 422B or 422C silicon conformal coating. Stay away from Acrylic conformal coating. The material fluoresces under a UV light, so you can see how well you cover the parts. You may need to apply multiple coats to get all the nooks and crannies.

    Good luck.

    Dual filter:

    1670288370156.png



    Single filter:
    1670289823674.png
     
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    bob311

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    Wow, I can't thank you enough for the detailed response. I know this is going to take some trial and error so I will try to post up some before and after results with different noise filters and dc to dc converters.
     
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    ShadowX

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    Wow, I can't thank you enough for the detailed response. I know this is going to take some trial and error so I will try to post up some before and after results with different noise filters and dc to dc converters.
    This looks promising for marine use. Its all fully encased so its waterproof except for the connectors. The 30A version is $27 from Amazon. Just search "waterproof 30a filter" in Amazon. Its good for 12V/24V/48V so it should work well for boats.

    1670309056132.png

    1670309368404.png


    You just hook up the wires and find a place to mount it in a dry location. If you twist your power and ground lines as a twisted pair, it also helps to reduce interference also. The spiral of the wires help cancel out some of the RF noise that is induced onto the wires. The interference affects both wires since its next to each other so it cancels out. This includes magnetic and other RF generated noise from other equipment nearby. This is called "radiated emissions". Shield of the wires also help reduce this type of noise from getting into your wires.

    s-l500.jpg


    Noise from alternators travel inside the wires so that type of noise is not cancelled by the twisting of the wires or wire shielding. This type of noise is called "conducted emissions". You want to knock both types of noise down. Best way to knock this type of noise is with inline filters similar to what you are trying to do.

    Another way is to add filter capacitors close to the alternators. This way, you knock down the noise at the source. These types of noise capacitors are common on automotive alternators.

    1670310591918.png


    Another way is to change your spark plugs to the type with a resistor inside. The ceramic resistor inside these plugs help reduce electrical noise also. There is a ton of ways to reduce noise if you have a lot of money and time.

    Spark-Plug1.jpg
     
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    Day0ne

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    ShadowX

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    It seems like 150A is way overkill in my opinion. Its best to just have a separate circuit where you want cleaner DC and only filter the DC going into those equipment. That includes the fish finder, radio, any other noise sensitive electronics, etc. I think 30A is already way overkill for most electronics. You really don't want to have other noise sources like pumps or motors on the clean DC side. You want to keep the dirty and noisy components before the filters. Lights and other circuits can be on the dirty side too since they are not sensitive to high frequency noise.

    Make sure you use a power isolator on the N2K backbone if you have a cable from your engine to display the data on the fish finder. You don't want noise to come back from the NMEA 2000 cable to the backbone from the engine wires either.
     
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    sickcat

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    Have you tried the ferrite filters that clamp over the wire?

    Cheapest and easiest solutions - KISS!
     
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    bob311

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    i have not tried any filters or isolators at this point, but will start with a smaller filter at the device like ShadowX has suggested. I never wanted to clean the whole system, only the fish finder and radio that are sensitive.
     
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    ShadowX

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    Have you tried the ferrite filters that clamp over the wire?

    Cheapest and easiest solutions - KISS!

    Round toroid cores with wires going around the core provides the best performance. The clamp down ferrite bead helps, but its not as good performance wise. The circular cores create the best magnetic flux so they work better when you have the space. The circular cross section makes them more efficient.

    The clamp on ones are more convenient to put over wires but the performance depends on how tightly wound the wires are to the core. Some people make multiple circular wraps around the ferrite to improve the performance.

    The performance of just adding ferrite is never going to perform as well as a properly designed low pass filters like the ones I show. It includes both the toroid inductors and capacitors to short out the high frequency noise. On the output end, you usually have several capacitor sizes to cover more frequency range. The smaller size capacitors work better at higher frequencies than the larger capacitors. By stringing them together in parallel, each cap is optimized to knock down the noise at different frequency range and work together.
     
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    kwik_wurk

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    Most problems arise in the small gauge signal wires the are unshielded or not having properly grounded drain wire. So ensuring those are properly arraigned and not on top of main power lines will be a huge help.

    DC grounding also needs to be accounted for on all components and ensure you’re not creating ground loops. (As the loops will pick up RF/EMF noise as well.)

    Suggest isolating power for these:
    MFD (aka GPS/Fishfinder)
    VHF (and AIS components)
    Radio (AM/FM)
    N2K backbone
    Network hubs (if used)

    Where it gets tricky is crossover components like N2K connected to stuff like autopilots etc…. or the engine displays that also talking to the MFD.

    If you open most electronics up, first thing on the power input are ferrites on the cables, then inside caps and possible torpid for LP filters blocking all that high freq noise. So most are actually ok with noisy power unless it’s out of control. (which may be an alternator issue, not an electronics issue; not saying you have either)

    (Also you wiring diagram seems to be missing a few things, like isolation switches. etc - I assume since you put an o-scope on the power, you know what’s missing.)
     
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    bob311

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    Unfortunately it looks like this is now a end thread for me. My lower unit started making a nasty growl and drained a milkshake with sprinkles... I have decided to repower with a pod and a Yamaha 300. Thank you all for the info, this may be revived once the repower is done.
     
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