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MPPT + DC-DC = (cheap) B2B

Solar DC-DC B2B Hack Battery Charger

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#11 rando

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Posted 04 October 2019 - 08:23 PM

I honestly can't say why you are only getting 2-5A into the battery - which MPPT charger do you have and are you sure the settings are correct?  

 

You do not need to ground the output of the DC-DC converter to the frame - it should just go into the solar panel terminals on the charge controller.   Do you also have a solar panel hooked up to the input to the input?


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#12 wiredinoc

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Posted 04 October 2019 - 10:09 PM

OK that's how I'm hooked up. What did you mean by a common ground then?

 

I do have a solar panel but its the suitcase type. I only unpack it when parked and disconnected from the vehicle.

 

I haven't made any changes to the MPPT, solar works fine. I'm wondering if the 48v is too high. I just ordered that 24v 20 amp model you posted to give it a shot.

 

Victron 100/20 mppt


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#13 rando

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Posted 23 February 2020 - 08:38 PM

Quick update on this project.   Used this for a week out in the desert in some overcast conditions and it worked beautifully.   I set the charge controller for 20A charge current, and after a night of furnace use and charging laptops I managed to pull nearly 60Ah out of the battery.  Driving for ~3 hours the next day I was back to 95% full, then the solar did the rest.   I saw no issues pushing 20A through the charge controller (and 12A through the DC-DC converter) for hours at a time, and when I stopped the solar charging also worked just as it should. 

 

Anyway, this is officially a proven success.


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#14 superduty

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Posted 19 July 2020 - 08:11 PM

@rando does the starter battery receive a charge from the solar when the vehicle is not running?


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#15 rando

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Posted 19 July 2020 - 08:47 PM

If the switch is in the 'down' or bi-directional charge position, then the starter battery is also charged.   When I am not using the truck/camper I leave the switch in this position to make sure the truck battery is always fully charged.   This, to me is one of the biggest drawbacks of a normal DC-DC charger.  

 

Also, since installing this, I noticed my SPDT switch would get a little warm when running 20A thought it, even though it is supposed to be rated for 30A.   I replaced the toggle switch a battery selector switch:

https://www.ebay.com...vUAAOSwawZbUodo


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#16 superduty

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Posted 19 July 2020 - 09:09 PM

@rando

 

What size wire are you running from:

 

A.  Starter battery to Blue Sea 7611

 

B.  Starter battery to DC DC converter

 

C.  Blue Sea to House battery

 

 

With the Victron you were able to set up particular charge parameters to best suit your house battery.  Is there any potential  problem with that same charge parameter charging your starter battery?  Or is that parameter gone since the power passes through the house battery?

 

 

Are any diodes or fuses used anywhere in your system?

 

 

I think I am going to duplicate your system for the most part and want to make sure I understand it all.  Thank you for sharing this.


Edited by superduty, 20 July 2020 - 05:39 AM.

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#17 Vic Harder

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Posted 20 July 2020 - 05:22 AM

I'll jump in here if you don't mind...

 

You can set the parameters in the Victron app for the Orion DCDC converter.  

 

Not sure what you are asking here " Is there any potential with that same charge parameter charging your starter battery?  Or is that parameter gone since the power passes through the house battery?" since the DC-DC charger is one way from starter system to house system.

 

IF, you are asking if the Victron MPPT settings (which are customizable) will affect how the Solar MPPT system charges the starter battery via the bypass relay rando uses ... yes, they will.  It will apply those parameters to all the batteries it "sees" connected to it.  Since the truck battery will be some distance away over wires, it will see a less than perfect view of your starting/truck battery.

 

Regarding wire sizes:

 

A) In my system I run 2AWG welding cable

B) Same as above

C) Same as above

D) DC-DC charger to house batteries - 8G wire... largest I could get to fit the converter

E) The 2g cables from the truck to the camper are joined via anderson power pole connectors in the truck bed.  Those run to a 100A Blue Sea 285 series breaker.  From the breaker to the DC-DC converter is 8G.


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#18 superduty

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Posted 20 July 2020 - 05:47 AM

I'll jump in here if you don't mind...

 

You can set the parameters in the Victron app for the Orion DCDC converter.  

 

Not sure what you are asking here " Is there any potential with that same charge parameter charging your starter battery?  Or is that parameter gone since the power passes through the house battery?" since the DC-DC charger is one way from starter system to house system.

 

IF, you are asking if the Victron MPPT settings (which are customizable) will affect how the Solar MPPT system charges the starter battery via the bypass relay rando uses ... yes, they will.  It will apply those parameters to all the batteries it "sees" connected to it.  Since the truck battery will be some distance away over wires, it will see a less than perfect view of your starting/truck battery.

 

Regarding wire sizes:

 

A) In my system I run 2AWG welding cable

B) Same as above

C) Same as above

D) DC-DC charger to house batteries - 8G wire... largest I could get to fit the converter

E) The 2g cables from the truck to the camper are joined via anderson power pole connectors in the truck bed.  Those run to a 100A Blue Sea 285 series breaker.  From the breaker to the DC-DC converter is 8G.

 

 

 

 

 

 

 

 

My question didn't make much sense as I had a typo in it.  "potential" should have been "problem".   

 

i was wondering if there is a problem charging the starter battery (non lifepo) with the lifepo parameters (house battery).

 

Does the Blue Sea 7611 even allow the MPPT  to "see" the starter battery when the solar is charging the starter battery through the house battery?  If the MPPT is able to see the starter battery does that mess up the MPPTs measurements of the lifepo and then essentially mess up the charging parameters?

 

I hope this is making sense.   The way I understand it is on the great attributes of the Victron is the ability to use the preset or program your own parameters for batteries and thereby charge LIFEPOs in the best possible way.

 

 


Edited by superduty, 20 July 2020 - 05:49 AM.

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#19 rando

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Posted 20 July 2020 - 03:33 PM

I think Vic covered most of what you asked. 

 

One thing to note is that voltage drop is not important with a DC-DC charger, so there is no need to run heavy cables from the alternator to the camper.   The cables only need to be rated to carry the current - for ~20A we are talking about here 12AWG is fine.  Same is true between the DC-DC converter and MPPT.   The only place you want short/fat cables is between the MPPT and the battery.

 

There are breakers at both ends of the wire between the alternator and ACR.   There are no diodes in the system. 

 

Program the MPPT for your LiFePO4, the starting battery will also see these voltages when in bi-directional mode as it is effectively in parallel with the house battery.   But you are really only float charging the starting battery, it is not that picky.    The LiFePO4 won't be negatively impacted by the truck battery in parallel.  


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#20 superduty

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Posted 20 July 2020 - 03:55 PM






There are breakers at both ends of the wire between the alternator and ACR. There are no diodes in the system.

.



What size breakers do you recommend for these two spots?
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