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blyhigh
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Joined: April 13, 2006
Posts: 121
Location: The Beaver State of Mind
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 Posted: Sat Jul 11, 2020 1:13 pm Post subject: Dumb electrical questions |
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I have a Renogy DC to DC with MPPT 50 amp controller I'm wiring up to a 110 watt solar panel and a 50Ah aux battery. The Renogy wiring diagram shows the unit wired to the starter neg or a common ground. It also shows another neg wire running from the unit to the aux battery neg post. Q: Can I use a common ground for the second wire or does it have to go to the aux battery neg post as shown in the diagram? Can the two neg wires share a common ground?
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DanHoug
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Joined: December 05, 2016
Posts: 4799
Location: Bemidji, MN
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| Posted: Sat Jul 11, 2020 3:39 pm Post subject: Re: Dumb electrical questions |
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solar panels can have a high OCV, Open Circuit Voltage that can be lethal so they want the Renogy unit itself grounded in case there is a short of the panel contacts to the Renogy frame, and they want a good electrical ground to the battery it is charging and sensing the voltage on. wire everything as they say.
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-dan
60% of what you find on the internet is wrong, including this post.
'87 Westy & '89 Westy both 2.1 4spd
Past projects can be found at--
www.thefixitworkshop.com |
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fxr
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Joined: December 07, 2014
Posts: 2325
Location: Bay area CA
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| Posted: Sat Jul 11, 2020 3:55 pm Post subject: Re: Dumb electrical questions |
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| DanHoug wrote: |
| solar panels can have a high OCV, Open Circuit Voltage that can be lethal so they want the Renogy unit itself grounded in case there is a short of the panel contacts to the Renogy frame, and they want a good electrical ground to the battery it is charging and sensing the voltage on. wire everything as they say. |
Those '12V' panels each have an open circuit voltage of ~21V MAX, and in that diagram they are in parallel. No way is that lethal. Plus the short-circuit current on those panels is self-regulating to only a few amps. No worries there.
I do agree that if using multiple panels in series with an MPPT controller (no point with a PWM one) you can get up to lethal DC voltages. That is a different scenario, and not one that a Van user would sensibly consider.
So that is not the reason why they mention 'ground'. It's just that the negative connection can be either directly to battery negative OR to chassis (i.e. 'ground') - it doesn't matter which, as the battery negative will be connected to the chassis anyway. Just depends which is most convenient in each individual's circumstance. It is sensible to make each device have it's own separate connection to the common point, i.e. don't join up the negatives one after another onto one common wire. Only to chassis, or the neg terminal of the battery.
Personally I find it best to connect each device separately to chassis with each battery having a circuit breaker in that path, so disconnecting each battery can easily be done when maintaining (or just fiddling with!  ) the system.
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Jim Crowther
1984 1.9l EJ22 Westy Wolfsburg Edition
Vespa GTS 300 |
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blyhigh
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Joined: April 13, 2006
Posts: 121
Location: The Beaver State of Mind
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| Posted: Sat Jul 11, 2020 7:54 pm Post subject: Re: Dumb electrical questions |
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| Thanks for the input. To clarify, I'm connecting both the charger/controller and the aux battery to the chassis with individual wires. Was questioning if the second wire shown in the diagram had to go to the battery neg or, using a separate wire, could I ground to chassis. And can I double up on the chassis ground for the two neg wires coming off the charger/controller? |
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fxr
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Joined: December 07, 2014
Posts: 2325
Location: Bay area CA
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| Posted: Sat Jul 11, 2020 8:10 pm Post subject: Re: Dumb electrical questions |
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| blyhigh wrote: |
| Thanks for the input. To clarify, I'm connecting both the charger/controller and the aux battery to the chassis with individual wires. Was questioning if the second wire shown in the diagram had to go to the battery neg or, using a separate wire, could I ground to chassis. And can I double up on the chassis ground for the two neg wires coming off the charger/controller? |
You can double-up, triple-up, whatever you like, as long as at least one of them is a good conductor. 
_________________
Jim Crowther
1984 1.9l EJ22 Westy Wolfsburg Edition
Vespa GTS 300 |
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blyhigh
Samba Member
Joined: April 13, 2006
Posts: 121
Location: The Beaver State of Mind
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| Posted: Sat Jul 11, 2020 8:12 pm Post subject: Re: Dumb electrical questions |
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| All marine grade and tinned copper, wires and terminals. |
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