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panel sharing?

Airgap

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Mar 11, 2022
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Can I connect two MPPT devices to the same set of solar panels? I want to set up a battery maintainer circuit for my truck engine battery. I have 6, 0ne hundred watt panels on my camper shell.
The panels run through a Victron Mppt and keep my camper lithium batteries charged.
When the truck is sitting parked for weeks at a time, I would like the same panels to maintain the battery. The charge controller for the lead acid truck battery would be disconnected from the both the panels and the truck battery when the engine is running.
Will the two differently rated MPPT devices interfere with, or harm each other , if they are both drawing power from the same panels at the same time?
 
I would like to understand the why it won't work. I can run various loads simultaneously off a battery or the the grid. What is it about using panels as a source that makes powering dissimilar MPPT device impossible?
I appreciate your answer and would like a better understanding.
 
No that won’t work. But you could separate 1 from the others and use it. Then swap back when you go on the road.
Probably be easier just to get a dc-dc charger. If he's incorporating alternator charging, renogy makes an all-in-1 dc-dc isolating charger with MPPT inputs that will allow alternator charging, keep the batteries isolated when the engine is off, and will maintain the chassis battery as well. Renogy isn't the only brand that makes these.
 
I would like to understand the why it won't work. I can run various loads simultaneously off a battery or the the grid. What is it about using panels as a source that makes powering dissimilar MPPT device impossible?
I appreciate your answer and would like a better understanding.
I can't pretend to explain it thoroughly, but it has to do with the way the technology works. The maximum power point tracking algorithm of one device will interfere with the other. Someone else will be able to better explain this than me.
 
Probably be easier just to get a dc-dc charger. If he's incorporating alternator charging, renogy makes an all-in-1 dc-dc isolating charger with MPPT inputs that will allow alternator charging, keep the batteries isolated when the engine is off, and will maintain the chassis battery as well. Renogy isn't the only brand that makes these.
I have been moving my victron camper set-up from vehicle to vehicle over the years. I like to keep the camper charging separate from the vehicle alternator.
Separating one panel makes sense but re-wiring the combiner box, adding switches and connectors is likely more complicated than adding a dedicated panel.
I was hoping the separate charging systems could share the power source.
 
Will the two differently rated MPPT devices interfere with, or harm each other , if they are both drawing power from the same panels at the same time?
Apart from a possible loss due to inefficiency it should work for what you plan to do with it. Neither CC will ''see'' the other - only changes to voltage as load changes and this wouldn't be any different to what occurs with clouds and shadows. Once one battery is full then the other gets sole use anyway.
 
Apart from a possible loss due to inefficiency it should work for what you plan to do with it. Neither CC will ''see'' the other - only changes to voltage as load changes and this wouldn't be any different to what occurs with clouds and shadows. Once one battery is full then the other gets sole use anyway.
Yes , this what I imagined however several people including a solar equipment salesman have told me it won't work. So I have become concerned that I might smoke some expensive component out of ignorance. I am still collecting information.
Assuming this idea will work, or even if I add a panel, my next question is which MPPT device has found favor with people who charge lead acid batteries?
 
Neither CC will ''see'' the other - only changes to voltage as load changes and this wouldn't be any different to what occurs with clouds and shadows.
Just to clarify: so the mppt sample ’signal’ doesn’t confuse each other?
That was my understanding of what happened with ‘one’ panel being sampled by two separate mppts. The fluttering millisecond loading to calculate mppt by one unit would “confuse” the other.
 
That was my understanding of what happened with ‘one’ panel being sampled by two separate mppts. The fluttering millisecond loading to calculate mppt by one unit would “confuse” the other.
The op is only maintaining the batteries and not looking for full efficiency. If the mpp isn't found should not be a problem.
Even if they do work a 2nd controller may not be the best option for the trickle charge required.
 
I was hoping the separate charging systems could share the power source.
They can. Don't add an MPPT on the panels, add a DC-DC between your house system and your chassis system. How is this any different than running wires from the solar panels? Quick disconnect plugs can be used either way. Regardless what you do, you will have to run cable to your chassis battery.

Edit:

And since you're considering some kind of charge controller and running cables to the battery, may as well consider this thread:
https://diysolarforum.com/threads/renogy-dc-dc-charger-w-mppt.1406/
 
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Assuming this idea will work, or even if I add a panel, my next question is which MPPT device has found favor with people who charge lead acid batteries?
Maybe a better idea is one of these....go for the 5amp and 12.6v


....derpsy doodler posted while I was writing.....
 
Maybe a better idea is one of these....go for the 5amp and 12.6v


....derpsy doodler posted while I was writing.....
Reading the interesting and helpful reponses gives me some good ideas and reminds me how shallow my knowledge is.
One thread led to a very capable device by Renology. At $300 it is likely over kill, considering I have a charger in line for my lithium set-up.
I do like the many features.
There is also a link for some much less endowed chargers
27.88US $ |DC DC Battery Charger 12v 24v to 12v 12.6v 13.v 14.5v Lead Constant Current 5A 8A 12A 15A 20A 22A 25A CC Battery Charger|Inverters & Converters| - AliExpress
These seem to have fewer or no protections for the battery being charged (constant currant).
This is where my ignorance really starts to pinch. In both cases the devices are described as working with power sources of lessor wattage than my array. The Renology device is linked to use with 400 watts. My panels are rated at 600watts.
In my experience Watts are a function of power used as opposed to voltage which is more like pressure to be wary of. Practically speaking , I can put a 10, 40, or 60 watt lamp into a socket and none will be harmed even though my outlet is rated 1500 watts. However when I suggest attaching a solar device like an MPPT to my panels 95% of the people I talk with tell me the 600 watt panels will destroy the 400 watt rated device.
I am thinking it is "headroom" and my advisors (generally parts salesmen) consider the extra watts as device killers. Hence I am on this forum hoping for a better understanding.
Finally, having just recently moved to the Northeast where my camper and I have for the first time experienced below freezing temps, I disconnected my Lithium batteries for the season. I hope to build a self sustaining heated battery box once we are settled.
For now, The panels on my camper are serving no purpose. The starting battery in the truck is not enjoying being parked for days in the cold weather. Twice I have gone out to run the motor for a twenty minutes session and found the battery flat.
No doubt there is a parasitic leak complicating things. This starting battery also deserves a heating system in the future. But for now I want to charge it with solar energy, hopefully using the panels I have.
PS I realize this is a very long "reply"...possibly bad etiquette..... a long with Solar, I am just learning about forums
 
I am just learning about forums
Learning is what they are all about....and thinking!

The storage Vs are FLA 12.6v and LiFePO4 13.25 (80%?) so anything to maintain these Vs is what you need. Over charging can be as bad as undercharging.
 
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