How large a fuse?

oldmakooldmako Registered Users Posts: 9 ✭✭
Greetings.  Fist post from a total neophyte.    However, I enjoy ridicule and shaming, so let er rip!

Here's my dilemma.   I just bought a small, 100watt solar panel to install on the roof of my boat.   I'd like it perform as a trickle charger only, for the times when the boat is not in use.  It will be mounted flat, not perpendicular to the sun.  It came with a 7 amp charge controller which I understand needs to be fairly close to the batteries.   I am using two group 31 Marine Deep Cycle batteries with 800 cranking amps, 650 CC Amps.    The charge controller will be wired to only one of the batteries.   But, I will use a pig tail with alligator clips to tie the batteries together in parallel (ONLY) when the boat is not in use in order to keep both batteries charged up. I have several questions.

It looks to have either 8 or 10 gauge wires leading from it, but only about two feet in length.  I have to extend these wires about 8 feet to reach the charge controllers location, near the batteries.  

1.  Do I need to use the same gauge wire for the extension?  I need to snake it though some piping to reach the batts.   At least two 90 degree bends will be required.  So, a smaller wire would be beneficial.
2.  Do I need to install an inline fuse between the panel and the charge controller? 
3.  If so, what size?
4.  Do I need fuse between the CC and the battery? 
5.  If so, what size?
6.  The wiring to and from the CC is small gauge, perhaps 14.   Will this cause problems if I use a larger gauge wire on the extensions from the solar panel?

Many many thanks.  I am psyched to finally have a solar panel on my boat.  I have wanted to do this for a long time.

Steve

Comments

  • mcgivormcgivor Registered Users Posts: 1,304 ✭✭✭✭
    Welcome to the forum Steve

    1. You could use a smaller gauge, overcurrent protection must be sized for the smallest gauge.
    2. Yes
    3. 10 A assuming 14 AWG 
    4. Yes 
    5. 10 A assuming 14 AWG 
    6. Larger is better, same rule applies as #1

    Using the largest gauge of wire possible is beneficial to reduce voltage drop, #14 is not the best choice as volt drop would be >2%, # 12 would be better, volt drop ~ 1.3%, based on maximum current, lowest voltage and 8 feet. The battery fuse should be close to the battery,  10 A is fine with #12 as its lower than the maximum current capacity. Here is a link to a volt drop calculator which can be useful. http://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=8.286&voltage=14.4&phase=dc&noofconductor=1&distance=8&distanceunit=feet&amperes=7.5&x=34&y=16
      1500W, 6× Schutten 250W Poly panels , Schneider 150 60 CC, Schneider SW 2524 inverter, 8×T105 GC 24V nominal 

  • oldmakooldmako Registered Users Posts: 9 ✭✭
    Many thanks!   I will endeavor to use the largest gauge wire that I can, up to the size of the wire coming out of the back of the solar panel and fuse accordingly.
  • EstragonEstragon Registered Users Posts: 1,616 ✭✭✭✭
    The short leads from a panel are typically 10ga, with MC4 connectors, one male and one female. These are often extended by buying a single MC4 extention cable a bit over twice the length needed. This cable is then cut in half, leaving one half with a male connector end and a bare end, and the other half with a female connector and bare end. The ends with MC4 are used on the panel connectors, which makes for a relatively secure, weather resistant connection. Some panel warrantees are voided if the connectors are cut off to make a bare wire connection.

    Making the wire from controller to batteries heavy and good connections is especially important. If the voltage drop is high on that connection, the controller may undercharge the batteries. Pigtail and clips could introduce a drop. I would test voltage at the controller output and at the battery posts. If more than 0.1-0.2v difference, I'd look at an alternative.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • BB.BB. Super Moderators Posts: 26,872 admin
    There can be lots of details about fusing(breakers), wire diameter, wire insulation type, ambient temperatures, in conduit, etc. But, to give you an idea, here is the NEC (National Electric Code table)--Which is relatively conservative:

    https://lugsdirect.com/WireCurrentAmpacitiesNEC-Table-301-16.htm

    And then the Marine wiring--I believe assuming no conduit--open air wiring and SAE wire gauge (which ~6-12% smaller in diameter than NEC American Wire Gauge and carries less current):

    http://www.boatus.com/boattech/articles/electrical-wiring-on-boats.asp

    I like to be conservative--And heavier wire has less voltage drop which is very important for 12 VDC circuits and longer wire runs.

    A couple of suggestions... Try to use good quality circuit breakers--They provide both current protection and make a handy on/off switch. Fuses are not good for on/off switches (especially when switching under load).

    I suggest not to use battery/alligator clips. They tend to be very unreliable and have relatively high resistance. Use bolted up connections and either Anderson Power Pole connectors (popular DC connectors) or even an A+B Switch:

    https://www.solar-electric.com/catalogsearch/result/?q=Power+pole+anderson (smaller and larger current versions available)
    https://www.solar-electric.com/blseabaswon3.html (single circuit battery switch)
    https://www.solar-electric.com/miblseabases.html (A+B battery switch)

    Note, I am not a fan of A+B switches--But it would be very nice for your needs (try not to switch them under load--They will fail sooner if switched under heavy current). If you loads are small (i.e., not cranking the boat's engine--You can use smaller switches vs the above battery bus switches).

    And for solar/off grid power--I always like to run the circuits at derated current. For example, a 15 amp circuit (14 AWG NEC typical) * 0.80 NEC derating = 12 Amp continuous load. Or, if you have a 20 amp load then 20a*1.25NEC= 25 amp rated breaker/fuse/wiring branch circuit.

    Typical fuses and breakers will not trip at 80% of rated current and will eventually (minutes/hours) trip at 100%+ of rated current.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • oldmakooldmako Registered Users Posts: 9 ✭✭
    edited October 8 #6
    OK.  More great info.   Im a bit overwhelmed now.  I'll try and respond to your posts as best as I am able, tho much of what you guys type is above my (very) limited level of knowledge...

    WRT the panel, it does not have connectors, just 10 (And that's a guess) ga wire with bare ends.   To these I am planning on using marine grade butt / crimp connectors which also have heat shrink "fittings".   I will also add tube style heat shrink over them with a healthy overlap.    The boat lives on a salt water creek and my experience has been do it right the first time, or you end up doing it again later.

    I purchased 10 ga wire yesterday for these leads.  They will run from the panel to the fuse (or, now that you mention it, a circuit breaker) and then to the charge controller.    Here's the part I am having issue with.   The wires from the controller, both FROM the panel and TO the battery are much smaller ga.   Perhaps 16.  I guess I got an el cheapo controller as I would have expected to see beefier wires.  This bugs me when I read suggestions to use heavier ga wire as they make good sense to me.

    This was a Costco Special.  It was only 129 bucks.   The panel I received appear ubiquitous on the web.  As I search it shows up frequently as "Renogy".   My panel is identical except for the controller and the connectors.   My controller is labeled as "Coleman". 
    https://www.amazon.com/dp/B00B8L8MD2?psc=1

    WRT alligator clips - You just gave me a great idea!  Here's a possible scenario.   

    I am also replacing BOTH of my battery selector switches.    They are Perko 8501's with 1 / 2 / BOTH / OFF selections.   Perhaps I'll take one of the old ones, and place it between the two batteries.    For clarity, the two batts are identical but only one will be wired directly to the charge controller.  Then, I'll run leads from the primary batter to the Perko switch so that I can select the secondary battery ON (to receive charging when the boat is not in use).  My goal is to keep both batteries topped off since the boat sits, often for months (winter) with little use.

    If possible, I'd like to set this up so that at least one BATT is receiving current while the boat is in use.   I often fish at anchor and run electrical appliances with the engine(s) OFF.  I typically turn one batt OFF in this situation in order to save it for starting the engines.

    But, maybe I'm missing something much more obvious.  Could I use one of the old Perko switches in a different manor to control the output from the controller??

    For example - What if I paired two positive leads leads from the controller?   The first would go directly to the primary (closest) battery.  The second would go to the Perko switch, say position 1.   The output of the perko switch would then be wired to the second battery.  That way, I could simply reach in and use the switch to direct current TO the second battery when I leave the boat.  Would that work?

    I should add, the two batts are reasonably accessible, but not out in the open.  Being able to reach into the compartment and simply rotating the switch would be much easier than attaching the alligator clips (in addition to being far more secure and safe).




  • littleharbor2littleharbor2 Solar Expert Posts: 704 ✭✭✭✭
    Controllers shouldn't have PV power coming into them without the battery already connected. That being said you would need to switch off PV prior to switching battery banks. Not a good idea, too much potential to fry your controller. BTW the Coleman controller you refer to couldn't be any cheaper. Spend a few bucks on something better.

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric, 700 ah @24 volt AGM battery bank. Plenty of Baja Sea of Cortez sunshine.

  • oldmakooldmako Registered Users Posts: 9 ✭✭
    edited October 8 #8
    I'm slightly confused -

    PV? Photovoltaic? 

    I will have the controller output connected to the primary batter before connecting the solar panel.  I don't understand this comment -"you would need to switch off PV prior to switching battery banks".  Sorry that I am making this so difficult.

    Will it be harmful to leave the controller connected while I'm running the boat?  I figured that I could just leave the primary battery connected when the boat was in use.

    Or, should I use the Perko to shut the whole thing off when I'm running the boat.  Would that be harmful having all that potential wattage just running into the controller with no output?

    Thanks for your input, especially about the Coleman controller.  It looks like cheap crap.  Is there one you would recommend for my application?

    Thanks.
  • BB.BB. Super Moderators Posts: 26,872 admin
    In general, solar charge controllers should be connected to the battery (bank) first, then connected to the solar panels.

    If you connect the PV (solar) panels first, then the battery bank, it is possible for the solar charge controller to become confused (most controllers get the power for their computer from the battery bank, and select 12/24 volt charging--If you connect solar panels under sun first, then the controller may not boot up correctly).

    If you always have the controller connected to Battery "A", and switch battery "B" when needed to battery A, there should be no problem. Note that if battery B is very discharged, it can pull lots of current from battery A until they are evenly discharged.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • littleharbor2littleharbor2 Solar Expert Posts: 704 ✭✭✭✭
    One of the small Morningstar controllers are a solid choice.

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric, 700 ah @24 volt AGM battery bank. Plenty of Baja Sea of Cortez sunshine.

  • oldmakooldmako Registered Users Posts: 9 ✭✭
    How about if I just use the Perko to distribute the charge?    Controller output to the common lug on the back and the two batteries connected to the 1 and 2 lug.

    When I use the boat, I select OFF and let the alternators do their job.   
    When I leave the boat, I select ALL and use the solar.

    The only downside I can see is that the two batts are charging in parallel and linked.  In case one goes bad, it pulls down the other.
  • mcgivormcgivor Registered Users Posts: 1,304 ✭✭✭✭
    Its ok to leave the controller connected while the engine is running because it will simply see the voltage as being high and reduce current out. What's being said is, when the switch is moved from one position to another, the battery will be disconnected momentarily, this will in effect shut the controller off, the panel voltage will spike to around 21-22.5 volts, possibly causing damage, or the auto voltage selection may choose 24V as the nominal voltage, because 22V is closer to 24 than 12,  causing the controller to not charge, if it is not already damaged. That is the reason for disconnecting the solar before switching battery positions. Connection procedure, battery first solar last. Disconnect in reverse order, solar first, battery last.


      1500W, 6× Schutten 250W Poly panels , Schneider 150 60 CC, Schneider SW 2524 inverter, 8×T105 GC 24V nominal 

  • oldmakooldmako Registered Users Posts: 9 ✭✭
    OK great.  Perhaps I am over thinking this.   If I can just leave them connected and not worry about over-voltage while under power then I'll do that.
  • EstragonEstragon Registered Users Posts: 1,616 ✭✭✭✭
    The issue isn't overvoltage under power.  The issue (I think) is having a break-before-make switch between the controller and the batteries.  This means the controller loses battery voltage and only sees array voltage, at least momentarily.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • oldmakooldmako Registered Users Posts: 9 ✭✭
    Got it.  I ordered a switch and will install it to prevent this.
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