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DCDC and solar MPPT charger questions


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#1 skifishbum

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Posted 27 June 2022 - 03:23 AM

Hey all,

I am having an issue with my new victron DCDC unit charging my campers lithium battery via the alternator. When I disable the “auto check engine” feature I can see 300 to 400 watts flow through to the battery. However when I have the “auto check” enabled it always gives me the attached message. Do I need to adjust the settings to get this to work? I have a newer truck that has a smart alternator.

I have also seen a few threads regarding solar wiring size. Just wanted to confirm 12 gauge is safe to run with around 220 watts of solar panels. Seems there is some debate which size is best. I’d definitely prefer to keep the stock 12 gauge if it’s not a safety hazard. Rewiring through the headliner does not look fun!

Thanks in advance, first time messing with electrical.

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Edited by skifishbum, 27 June 2022 - 03:26 AM.

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#2 Vic Harder

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Posted 27 June 2022 - 03:43 AM

Hey all,

I am having an issue with my new victron DCDC unit charging my campers lithium battery via the alternator. When I disable the “auto check engine” feature I can see 300 to 400 watts flow through to the battery. However when I have the “auto check” enabled it always gives me the attached message. Do I need to adjust the settings to get this to work? I have a newer truck that has a smart alternator.

I have also seen a few threads regarding solar wiring size. Just wanted to confirm 12 gauge is safe to run with around 220 watts of solar panels. Seems there is some debate which size is best. I’d definitely prefer to keep the stock 12 gauge if it’s not a safety hazard. Rewiring through the headliner does not look fun!

Thanks in advance, first time messing with electrical.

Welcome to this forum skifishbum!  I'll try to address your questions.  Lots of smart folks here, so I hope they chime in too.  First off, Yes, you do need to adjust the settings.  Here is why:

 

If you have the stock wiring between truck and camper, there will be a lot of voltage drop when passing 400watts.  As a rough guess, 400/13v = 30amps of current are going across those wires.  The factory breaker is 30A, so you are right on the edge of that.  30A over 14g (usual RV sized wiring) over 25' (distance from alternator to camper batteries) = about 7 volts. Yes, 7 volts.  Meaning that even if you did not have a smart alternator and are putting out 15v, by the time it gets to the DCDC, it only sees 8v.  And the DCDC concludes that the truck is not running.

 

Bigger wires from truck to camper are needed, OR, you wire in the switch to manually turn on the DCDC or you do as you have been and disable engine running detection.  

 

On the solar wire size question, I have 330W on the roof, in a single panel, and am using 12g wire.  220W should be fine. What solar charger are you using?  If it is a MPPT, it will usually salvage the power delivery by compensating for the voltage drop.  What are you using to generate 220W?  One panel?  Two in parallel or in series?


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Building out an electrical system - So, you want to setup a good electrical system in your camper? - Electrical, Charging, Solar, Batteries and Generators - Wander the West


#3 skifishbum

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Posted 27 June 2022 - 04:03 AM

Welcome to this forum skifishbum!  I'll try to address your questions.  Lots of smart folks here, so I hope they chime in too.  First off, Yes, you do need to adjust the settings.  Here is why:
 
If you have the stock wiring between truck and camper, there will be a lot of voltage drop when passing 400watts.  As a rough guess, 400/13v = 30amps of current are going across those wires.  The factory breaker is 30A, so you are right on the edge of that.  30A over 14g (usual RV sized wiring) over 25' (distance from alternator to camper batteries) = about 7 volts. Yes, 7 volts.  Meaning that even if you did not have a smart alternator and are putting out 15v, by the time it gets to the DCDC, it only sees 8v.  And the DCDC concludes that the truck is not running.
 
Bigger wires from truck to camper are needed, OR, you wire in the switch to manually turn on the DCDC or you do as you have been and disable engine running detection.  
 
On the solar wire size question, I have 330W on the roof, in a single panel, and am using 12g wire.  220W should be fine. What solar charger are you using?  If it is a MPPT, it will usually salvage the power delivery by compensating for the voltage drop.  What are you using to generate 220W?  One panel?  Two in parallel or in series?


Thanks for the help! I have a victron mppt 130. I will most likely have one panel.
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