Solar Charger Tie In Location

Discussion in 'Wiring' started by generok, Aug 29, 2019.

  1. generok

    generok Well-Known Member

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    So, DW got me a Renogy 300W system for the TT and I am scoping out the install now. The charge controller has to be mounted inside, and the way I can get the solar power cables into the rig is right down the channel above the power converter, and I have some panel space to flush mount the controller right there.

    Now, here's where I have a bit of a question/doubt. Installation instructions say to run the output of the charger directly to the batteries. But, a much cleaner solution would be to tie in to the main battery cables coming in to the converter. In effect, it is the same exact thing. The resistance of the existing cable to the battery would be the same as the resistance I'd gain in running the cable all the way from the solar charger to the battery (and I'd have to poke more holes in the rig to run them).

    Is there anything I am overlooking? Converter is a WFCO 8955.

    Thanks!
     
  2. eoleson1

    eoleson1 Well-Known Member

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    Hooking to the battery cables at the convertor would be the same thing, assuming you have no corrosion or poor connections between the conv and the bat.
     
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  3. NavarWynn

    NavarWynn Member

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    It depends. But likely NOT ok.

    If the cables are of adequate size, and the battery connection is gudenclean (good and clean ;) ), you are absolutely right in that there is no theoretical difference in the circuit....

    ... However, a 300W charge controller has a power output rating of 30A, so (potentially) adding that current flow to your converter's (likely) 10awg cabling may (potentially) cause problems. You'll also have to break the B+ and B- lines and tie in there. If you do that incorrectly, you are introducing a resistance point.

    Further ... (and the biggest reason not to IMO), you would be introducing a power source AFTER the battery fusing. So a broken line shorting out, which pops the B+ line fuse, instead has no circuit protection - and potentially higher voltage. Now, a dead short would likely pop the charger's breaker - but also recall that, according to the manufacturer of the charger, you should never have your PV system active without the battery connected this is because the battery loads down the circuit voltage. So, if the B+ line fuse pops for any reason (with your proposed connection) you are going to have High open circuit voltage feeding directly into your converter. Obv. I don't know if doubling or tripling the designed feed voltage for the converter is going to kill it, but it certainly has the potential to do so - this also has the potential to burn the pup to the ground.

    ...THAT is the reason the instructions say to tie directly into the battery.

    In a nutshell, I wouldn't recommend tying in this way. However, were you bound and determined, at a minimum I'd install fusing between the converter, and the battery cable/charge converter tie in point, then maybe upgrade the wiring between that point, and the battery(?) ... May very well also have to uprate the B+ line fuse because, if it's only 30A, your charger might pop it (leading to the above mentioned problems...) ... like I said, I would recommend simply tying directly to the battery... easier (I think), and a crapload safer.
     
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  4. generok

    generok Well-Known Member

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    Good info. Thank you.

    The panels are above the fridge chimney and is essentially straight down to the converter. If I run to the battery, that's an extra 13' of run, plus extra for routing to hard points, so figure 15'. Currently, the battery cable into the converter is 8awg. The Renogy cable provided is 6 sqmm, which is between 10 and 8awg. So, I am better off using the installed 8awg. Good point on the fusing... Renogy also recommends fusing the charging circuit, so I will do that on the pos side. The negative side is a bus that all the negative sides of all 12V circuits and the converter tie into. Luckily there are a lot of open bus slots, so I can tie in there without having to cut cables at all. On the pos side, there's already a battery isolate switch, so I have a break in the 8awg between the battery and the converter which I will tie into, and install the in-line fuse.

    I think in the long run I will get less line resistance using the 8awg stock cable versus a 15' run with the Renogy 6 sqmm cable. Plus, my undercarriage is sealed with a single piece of plastic for arctic protection, and I would have to take the entire bottom apart to run cables under the floor along the frame.

    Your advice really got me thinking, and I ensured the Renogy install instructions recommended the same thing, and it did. So, I have to get some good splice connectors and get to work inside. Thank you for your thoughtful and thorough advice!
     
  5. rabird

    rabird Howdy!

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    Get the CC as close to the batteries as possible. For wire size CC to batteries keep it BIG.
    300 w @ about 5A / panel is 15A. 10' of 8 gauge would be acceptable to me! but still a tad small!
    A remote voltage sensor would help.
     
  6. NavarWynn

    NavarWynn Member

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    Yes, w/ 8awg cables, your cable condition is probably perfectly adequate. .... buuuuuut.... that doesn't resolve the principle source of risk.

    So your proposed circuit is as follows (from the description you have given us):
    upload_2019-9-3_10-53-38.png

    This should be fine, assuming your Batt (B+) Fuse is significantly overrated (say like 50-60A). What you are trying to avoid (under ANY circumstances) is 'Batt Fuse' from blowing, which could result in the CC feeding the converter (and other loads) with the Battery completely removed from the circuit. If this happens without the CC noticing (and coding out/cutting all output power), you have a significant risk of the CC damaging the converter and/or other loads. PWM CCs aren't like an old, dumb, coil/transformer charger, they intentionally alter, and ramp up and down the output voltage and current in specific algorithms to 'properly' charge (and make the batt last as long as possible) whatever type of battery you have it set for. Such (B+ blowing) should code out the CC, but I've certainly seen improperly hooked up PWM charge controllers cook electronic modules, circuits, and other components.
     
    Last edited: Sep 3, 2019
  7. tfischer

    tfischer Well-Known Member

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    I put velcro on my charge controller, and stick it to the side of the battery box when deployed. The extended bunk shields it from weather, and I remove it when popped down (we have a portable solar setup so we don't use it when stored)
     
  8. SteveP

    SteveP Well-Known Member

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    The converter should have a blocking diode to prevent back feeding from the battery when shore power is disconnected. Might be able to verify this by contacting the converter manufacturer but it only stands to reason. If wired as above it would also protect the converter from back feed from the solar controller if the battery is disconnected. So if the battery fuse is blown the charge controller will see a battery disconnect and the main potential for damage is in the charge controller itself, receiving PV current with nowhere to send it.

    I don't see a need for the isolation switch in that location. But I would put one between the panels and the controller.

    I would want to combine the max output of the converter plus the potential 15.n amps from the solar controller and use that value for the fuse at the battery. It appears that a 70 amp fuse is the max on 8 gauge wire (https://www.bluesea.com/support/articles/Circuit_Protection/1441/Part_2:_Select_a_Fuse_and_Fuse_Holder_For_Your_DC_Product_Installation)

    One of the many things I don't have any idea about is the effect of trying to push charge to a battery that is pushing current to load through the same wire, which is avoided by the separate positive run from the controller to the battery. Presumably some charge controller current would be shunted of to handle load requirements, the remainder would go to charge the battery and the discharge from the battery will be reduced. It may work the same way when the circuits are joined at the battery post.

    I would be interested to see the results of a comparison between what the controller displays as charge voltage and amperage and a voltage and amperage test at the battery posts with this installation.
     
  9. SteveP

    SteveP Well-Known Member

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    I did see a post on Expedition Portal last night that stated the poster had seen damage to trailer electronics when he had a charge controller disconnected from the battery, so I'd like to amend this statement. But I think most people on this portal do not have a disconnect between the PV feed and the controller so it seems it should have happened here.
     
  10. NavarWynn

    NavarWynn Member

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    I think it totally depends on the type of CC used. modern PWM units have a much higher potential for doing damage to the TT's equipment than 'old style' units did. While they are absolutely the best as long as the battery remains in the circuit, if something cuts it out (say that B+ fuse in the circuit blows - for whatever reason), I've seen feed voltages from PWM chargers climb to double or triple the 'boost' (or 'opportunity') charge voltage before coding out and cutting output power. This sometimes happens because it is a 'smart' charger, and for it to be 'smart' it has to 'see' the system voltage while it is feeding the battery increasing (and decreasing) power. So, even though it is supposed to cut power when it detects no battery, a load, in this circumstance, can easily confuse it. ... and, while feeding your converter 30+VDC pulsed?... that may not kill it, but it SURE as HECK ain't good for it!
     
  11. generok

    generok Well-Known Member

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    Once I got in there, the main cable from the battery to the converter is actually 6ga. So, I tied in using a block our local auto electronic supply recommended. In the pic below, you see the 10ga inline fuse in the middle (and a 10ga inline fuse rig is VERY rare). I then tied in the B+ line on both sides. Very low resistance and fuse protected. 20190904_182026.jpg
     
  12. Grandpa Don

    Grandpa Don Active Member

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    I'd like to make a couple of comments on my solar installation. I have a 100 Watt system. I ran the cables directly to the battery with a fuse at the battery location. I didn't have to drill any new hole in the camper. I mounted the controller to the wall of the cabinet containing the Converter. In the floor of that compartment there was a hole where the wires come up through from the battery and going out to other 12 Volt things. So I already had a hole in the floor inside of the cabinet. After I cleaned all of the sealant away that was sealing up the hole I found that there was enough room left to run my Solar wires down through it. I secured them to the underside of the camper floor just like all of the other wires under there. The controller is mounted in such a way that I can monitor it while inside. All of the wires are stored inside the cabinet along with the extra 25 feet of Shore Power cable and the 25 feet of Solar cables. Be sure to hook up the controller to the battery before you connect the cables to the Solar panels. Also, I did not mount my panels permanently to the roof of the camper. Logic tell me that I want to park my camper in the shade. So with permanently mounted panels you would only get partial sunlight much of the time. I pull out all 25 feet of cable at the camp site and them move the panel around to catch as much sunlight as possible for as long as possible. I have folding and adjustable 45 degree support legs mounted to my panel so I can tilt it up more during high noon sunlight. I installed the whole system last year and so far everything has worked as planned on every trip.
     
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  13. mpking

    mpking Well-Known Member

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    @Grandpa Don,

    What kind of connector do you have on the cable that connects to the Solar Controller to the Panel?

    I never thought of mounting the solar controller in this location. My camper actually has a second hole in this location for the AC (which I don't have)
     
  14. Grandpa Don

    Grandpa Don Active Member

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    I got a complete kit that came with literately everything I needed to install. The wires that connect to the controller box were just stripped back wires that slide into a screw tightened connections. The ones that went to the battery already had the loop connectors installed. And the wires that went to the Solar panel had special in-line connectors that were made so that you could not cross connect them. I think I paid under $200.00 for the whole kit. The panel is a 100 Watt unit. 100 Watts is more than enough to keep my battery charged when boondocking. I did buy a supporting bracket that was meant to attach the Panel to the roof, which I just use it to hold the panel up on the ground.
     
  15. generok

    generok Well-Known Member

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    It is done and charging. We're probably going to boondock this weekend, so we'll give it a workout and see if we need to run the genny at all. 20190908_144858.jpg 20190908_131708.jpg
     

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