1. Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
    Dismiss Notice

Fuses or Circuit Breakers?

Discussion in 'Automotive Electronics' started by Tony K, Mar 8, 2017.

  1. Tony K

    Tony K Member

    Joined:
    Dec 20, 2016
    Messages:
    42
    Likes:
    0
    Hi,

    We spoke last week about fuses on my boat, 125 amp for each battery. The starter motor draws 200 amps but only for a few seconds so these will be OK. It would seem much more sensible however, to fit circuit breakers. If in the event of a mega fuse blowing it would be a fag to change it, much easier to reset a breaker.

    My question is to cope with the 200 amps of starter motor will a 100 amp or 150 amp circuit breaker be OK? I don't know at what time delay or current they actually trip?

    Actually thinking about this why not a 200amp CB is this OK?

    http://www.ebay.com/itm/Car-Audio-3...id=100005&rk=4&rkt=6&mehot=ag&sd=252763150061

    Cheers T
     
    Last edited: Mar 9, 2017
  2. cowboybob

    cowboybob Well-Known Member Most Helpful Member

    Joined:
    Oct 22, 2011
    Messages:
    3,050
    Likes:
    478
    Location:
    James Island, SC
    ONLINE
    I'd suggest a breaker with no less than a 200A trip point (200A Example). But, actually, 250A (250A Example) would be better.

    My rationale is that most breakers respond (trip) as the result of a thermal trigger. Thus, with an expected 200A draw, you'd be right on top of the trip point and for an extended period of time. This would, probably, result in annoying interruptions.

    The 250A (pricey, to be sure) would better suit the application by giving you protection in the event of a true short, without the interruptions.
     
  3. Tony K

    Tony K Member

    Joined:
    Dec 20, 2016
    Messages:
    42
    Likes:
    0
  4. dave

    Dave New Member

    Joined:
    Jan 12, 1997
    Messages:
    -
    Likes:
    0


     
  5. cowboybob

    cowboybob Well-Known Member Most Helpful Member

    Joined:
    Oct 22, 2011
    Messages:
    3,050
    Likes:
    478
    Location:
    James Island, SC
    ONLINE

    I couldn't determine whether the breaker listed is "marine" rated or not. In your application, I would require that.

    That might explain the considerably lower price.
     
  6. shortbus=

    shortbus= Well-Known Member

    Joined:
    Mar 23, 2008
    Messages:
    1,230
    Likes:
    77
    Location:
    youngstown, oh
    Maybe a dumb question, but why does a starter motor need a fuse? Like in a car the starter is unfused and all of the other accessories are fused after the starter cable. But that I mean the battery cable goes to the starter, then a wire comes from that point to the fuse block.
     
  7. Grossel

    Grossel Member

    Joined:
    Sep 16, 2008
    Messages:
    925
    Likes:
    22
    Location:
    Norway
    Probably to reduce the risk of destroy the battery in an event where the starter motor is prevented to rotate. It may have more serious consequences at sea in case where it's a need of calling for help by radio. Maybe one backup battery isn't enough for that kind of safety.
     
    • Like Like x 1
    • Thanks Thanks x 1
  8. cowboybob

    cowboybob Well-Known Member Most Helpful Member

    Joined:
    Oct 22, 2011
    Messages:
    3,050
    Likes:
    478
    Location:
    James Island, SC
    ONLINE
    I've had starters "seize" in cars and boats, i.e., as Grossel suggested. Most well equipped marine battery wiring assemblies include, at the least, a heavy duty rotary switch to select either: A battery ON, OFF or B battery ON.

    The seizures required that I remove a battery terminal cable which was an ordeal and took long enough to result in damage. Had it happened in my '01 Volvo V70, I probably would have lost the car since the battery is under a bolted down metal cover under the rear deck.
     
    • Thanks Thanks x 1
  9. Tony K

    Tony K Member

    Joined:
    Dec 20, 2016
    Messages:
    42
    Likes:
    0
    Thanks for all that. Got a new one for you.

    I am fitting a Blue Sea charging system to the two batteries in the boat. I would like a voltmeter for each battery to show condition of each. Will this work?
     
  10. cowboybob

    cowboybob Well-Known Member Most Helpful Member

    Joined:
    Oct 22, 2011
    Messages:
    3,050
    Likes:
    478
    Location:
    James Island, SC
    ONLINE
    TK,

    How will the batteries be wired (and used), i.e., separately (using 2 chargers) or in parallel (1 charger)?

    How you monitor their voltage level depends on the above. But keep in mind that a lead acid battery's voltage level does not indicate its capacity (energy density). This is best checked with either a hydrometer or a resistive load tester. Neither of these are used as a continuous indicator - they are only for periodic testing.
     
  11. Tony K

    Tony K Member

    Joined:
    Dec 20, 2016
    Messages:
    42
    Likes:
    0
    [​IMG]


    This is the wiring diagram for the Blue Sea set up found at

    https://www.bluesea.com/products/7650/Add-A-Battery_Kit_-_120A

    I do not have an outboard, but a 27hp diesel inboard with one 55 amp alternator. I got two volt meters because there are two batteries but where do I wire in the voltmeters to monitor battery condition simultaneously? Because, if the Blue Sea charging relay shuts off charging to one battery presumably I won't get a reading on one of the voltmeters? I a right about this or just dumb? Don't answer that last bit!

    Cheers
     
  12. cowboybob

    cowboybob Well-Known Member Most Helpful Member

    Joined:
    Oct 22, 2011
    Messages:
    3,050
    Likes:
    478
    Location:
    James Island, SC
    ONLINE
    OK. I see.

    Dual Circuit Plus™ Battery Switch

    • Simplifies switching
    • Isolates engine and house circuits
    • Combines batteries for emergency starting
    • Tin-plated copper studs for maximum conductivity and corrosion resistance

    ACR Automatic Charging Relay

    • Automatically combines batteries during charging
    • Isolates batteries during engine cranking and when not charging
    • Shares the charge between two batteries more efficiently than a battery isolator
    • Allows efficient dual battery charging without needing regulator adjustment or rewiring

    Nice rig.

    You can (if you so choose) put a separate voltmeter (VM) directly across each respective battery. From the ACR data above, though, they will not give you individual battery readings during charging (any time the engine is on), engine cranking OR when you use the Dual Circuit Plus™ Battery Switch set to the emergency starting position.

    Thus, VMs will only indicate true, unloaded battery voltage when the engine if OFF. And, as I said, this is not a valid battery condition indicator.
     
  13. Tony K

    Tony K Member

    Joined:
    Dec 20, 2016
    Messages:
    42
    Likes:
    0
    OK Cheers Cowboybob,

    So Ignition on, I can see what the state of each battery is,............ but then when the engine is started it won't show me what I was hoping. Will both voltmeters therefore read the same as a mean across both batteries, unless of course the ACR cuts charging to one or both out?

    Thanks again.
     
  14. shortbus=

    shortbus= Well-Known Member

    Joined:
    Mar 23, 2008
    Messages:
    1,230
    Likes:
    77
    Location:
    youngstown, oh
    Not a boat guy so didn't know. And must be really lucky, in over 50 years of driving and working on cars, my own and other peoples never saw a starter or heard of a starter seizing.
     
  15. cowboybob

    cowboybob Well-Known Member Most Helpful Member

    Joined:
    Oct 22, 2011
    Messages:
    3,050
    Likes:
    478
    Location:
    James Island, SC
    ONLINE
    If you have the system as shown in Post #10, the two batteries serve 2 loads: 1. the starter (and engine which includes the alternator) and, 2. the boats electronics. They can be combined (in parallel) for emergency purposes.

    As I understand the description of the operation of the Bluesea rig you posted, it appears the two batteries are charged simultaneously which, would, of course, puts the same voltage level on both batteries during the charging process. So, yes, separate VMs would be redundant.

    However, the ACR does, apparently, isolate the 2 from each other when OFF or if one or the other needs no charge. So, in that case, 2 VMs would be indicating separate voltage levels (i.e., Charging level or normal battery level values).

    However, given that I have no idea how the system might, eventually, be wired (there are other options), I'd suggest the following:

    One VM and a 3 position switch wired as below:
    upload_2017-3-10_18-38-19.png
    Just check the batteries as you see fit, always returning the switch to "OFF".
     
  16. Tony K

    Tony K Member

    Joined:
    Dec 20, 2016
    Messages:
    42
    Likes:
    0
    Thanks for that and thanks for the idea with a switch. It's clearer now for me.
     

Share This Page