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Thread: Split Charge system : How big a fuse do I need?

  1. #1
    Member norsk's Avatar
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    Split Charge system : How big a fuse do I need?

    I am in the process of installing some LED lights and a Diesel heater in my Camper,so I thought it was a good time to install a split charge system.

    My question is:How big a fuse do I need between the first battery and the Voltage Sensitve Relay? The one I am installing is rated for 125 Amps,should a 100 Amp fuse do the job?

    I will install a couple of USB ports and probably LED flood lighting around the outside of the box too,not that its really go alot to do with that circuit.
    "Sixty percent of the time,it works every time"

  2. #2
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    The fuse is there to stop the wire burning if a short circuit occurs but you can add up the load and make the fuse slightly higher that the total. Do you have the data on the heater and the LEDs? As long as the cable is big enough and the fuse rated lower than the cable you should be ok.
    mimms2 likes this.
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  3. #3
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    As above, fuses are there to burn before wires do.
    Only thing to consider (unlikely by sounds of your loading) is that if secondary side CAN draw more than 100A, then you'll be poping fuses.

    Can get thermal circuit breakers (resettable) or go hard out and install DC MCBs.

    Is the vsr not a three-prong job? ie alternator connected in centre and primary/secondary battery terminals? I imagine it would have built-in overcurrent protection (thermal, or internal fuse)...
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    I suppose your house battery/ies are a decent size. Those diesel heaters are neat, but if you have it running all night will use up a bit of juice. 10-11 amps on start up, settling back to 1-1.5 amps when running steady state.

  5. #5
    Member norsk's Avatar
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    Quote Originally Posted by XR500 View Post
    I suppose your house battery/ies are a decent size. Those diesel heaters are neat, but if you have it running all night will use up a bit of juice. 10-11 amps on start up, settling back to 1-1.5 amps when running steady state.
    Yes thats exactly what I found out from the internet too.

    The LED's in total draw 0.75 Watt

    Adding a USD Charger for Drone/Phone etc won't up the draw too much?The Calbe is going to have to be around 5 meters long,will that have anything to say?

    Its a truck battery I am installing so I could use it to star the truck if I needed to.

    I see what you mean about the heater drinking a bit of Diesel,I was thinking about plumbing it into the tank on the mog.It came with a 10L tank but I think just plumbing it straight into the truck tank plus carying a spare jerry can is a better idea.

    The heater is just to keep the inside warm while I am away during the day,I might install the wood stove I had in the other one to keep things cozy at night.

    I will sort out the wiring on the LED's today and hopefully get the heater installed.
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  6. #6
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    Quote Originally Posted by norsk View Post
    Adding a USD Charger for Drone/Phone etc won't up the draw too much?The Calbe is going to have to be around 5 meters long,will that have anything to say?
    Everything will have a watts rating on it. Phone charger 1.1-2.4A at 5V = 12W, runs for say 5 hours a day = 60Watt-hours of battery needed there, add up everything else as well to determine your required storage capacity.
    Big cable TO house batt, then shorter runs, close to battery, can be smaller cable.

    Cable supplier should be able to give you ohms-per-foot, and/or a voltage-drop graph. 5 meters is starting to get long, especially if it's taking full charge current (80-120A @ 12V?)

    Its a truck battery I am installing so I could use it to star the truck if I needed to.
    Not if it's flat you wont...
    Quote Originally Posted by 308
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  7. #7
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    Welding cable (25mm^2) can normally be had cheap from wholesalers, as long as you don't mind the orange sheath.
    Good for few hundred amps at 12/24V.
    Quote Originally Posted by 308
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    Do you have a fuse between the engine charging and the start battery? It's not common in my experience to add any sort of fuseable link between a charging system and a battery as starting current inrush when the charging contact closes can be quite large momentarily, dropping back to a steady state within the first second.

    The purpose of a dvsr device is to parallel the house and start batts when the start batt voltage reaches a set figure and allow both to be charged, and same as joining two buckets when the first reaches tipping point it dumps a lot into the second. I've never fitted a fuse with marine dvsr installs, and I've fitted lots. Never replaced one apart from physical damage like dumbarse crushing the thing! Never fused the charging side either, between the battery and panel yes but that's a little different.

    If you were to install one, I'd go start current rated or motor rated and big to protect against inrush current popping it. And that would be $$$$$... As a question again have you ever seen a fuse between a battery and a starter motor!

    Check out Blue Seas product, not cheap but excellent and have a good look at their wiring diagrams. BEP marines gear isn't bad either, I might have a wiring diagram here somewhere.

    Cable, batt rated twin sheath and tinned, flexible cable (multi stranded). Some welding cable and solar pv cable isn't built the same, not recommended for vehicle use.
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  9. #9
    Member norsk's Avatar
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    I have a quite a bit of battery cable.The likes of which you would run to the starter on a truck.I will use that.

    I like the idea of a fusable link but I will hook everything up and see if there are any points the cable could rub through.I don't want an untidy mess but the house battery and truck battery are on opposite sides.
    "Sixty percent of the time,it works every time"

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    Re your cabin diesel heater, they are a brilliant invention, esp with the ability to program when you want it to start up. There's a dude on YT by the name of David McLuckie who's done about every conceivable test you can think of on those heaters. If you have any issues with it check out his channel.

    Mogs are great machines to get about the bush in. Go anywhere. Do anything.

  11. #11
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    Quote Originally Posted by norsk View Post
    I have a quite a bit of battery cable.The likes of which you would run to the starter on a truck.I will use that.

    I like the idea of a fusable link but I will hook everything up and see if there are any points the cable could rub through.I don't want an untidy mess but the house battery and truck battery are on opposite sides.
    If you have any really dodgy contact points or restrictions, a piece of electrical conduit can help. If round plastic pipe is too fat a smaller size heated with a heat gun and pressed oval will work. Used that once or twice in boats where we have had to upgrade cabling runs through alloy boats and we just couldn't get in to protect the cable and stop it rubbing through and earthing onto the hull... Otherwise good old corrugated split conduit does a power of work for you.

 

 

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