diy solar

diy solar

Sharing solar panels for multiple uses

RichDobbs

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Jun 16, 2021
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When car camping I want to share my solar panels between running my refrigerator (12v, 50 watts) and charging my e-bike battery (for use in my yet to be assembled e-bike kit, and as rainy day backup for the refrigerator). For collecting firewood, I'd like to use a 120v electric chainsaw, as well as charge various cordless batteries. I've got a large 12v inverter that should be able to run anything that a typical 15amp circuit can handle, and to handle surge loads I'm planning on using a modest 12V deep cycle SLA battery.

I want a system that just works, rather than requires me to either monitor it and plug and unplug things, or else reconfigure things using a GUI. I've got experience in using Arduino and Raspberry Pi's for automation.

My initial thought was to just throw a bunch of MPPT's connected in parallel, with each MPPT handling a particular battery chemistry. And then implement a charging policy either by figuring out the Victron API's or just using relays to direct the PV array at its highest priority use.

However, I've heard both that this will cause problems with the various MPPT's fighting each other (from a Victron moderator) and that it works fine (from successful users).

Given my reasonable goals, what is an effective approach to this sort of problem?

Best regards,

Rich Dobbs
 
Welcome to the forum.

You can't connect the same set of panels to multiple charge controllers.

You seem to be making this more complicated than is necessary. Since you haven't given additional information on "a particular battery chemistry," I'm going to ignore it.

12V panels connected to MPPT connected to 12V battery. 12V inverter connected to 12V battery.
Fridge runs off 12V battery.
All other devices run off "big" inverter sized for the chainsaw OR
Chainsaw run off "big" inverter and chargers run off smaller inverter sized for chargers.
"Big" inverter powered off when not needed to avoid idle power consumption.

Done.
 
Snoobler is right, you are making it too complicated. And having a system you don't need to monitor or tend generally requires having much more system than you actually need.
 
For camping fire wood a dc sawzall works good. A couple of charged batteries will cut a lot of wood. If you have to charge a small inverter will work.
 
For more information:

I don't want to always bring the big inverter and the heavy battery around with me while car camping.

I could size a smaller inverter to power the e-bike charger. But it would still be larger than the MPPT controller plus a relay, and would be slower in charging the e-bike battery unless I upgrade the e-bike charger and the inverter.

It seems to me that this system preferentially charges the e-bike battery rather than the refrigerator battery.
 
For camping fire wood a dc sawzall works good. A couple of charged batteries will cut a lot of wood. If you have to charge a small inverter will work.
That's a good idea. I already have an 18V Porter Cable Recip Saw. It's charger takes about 120 watts.
 
Snoobler is right, you are making it too complicated. And having a system you don't need to monitor or tend generally requires having much more system than you actually need.
What you think of as being too complicated, I think of being an interesting technical hobby, and part of the learning process, providing transferable skills that I can use on the job. That said, if I could just plug together parts and just get things to work, that would be great.
 
What you think of as being too complicated, I think of being an interesting technical hobby, and part of the learning process, providing transferable skills that I can use on the job. That said, if I could just plug together parts and just get things to work, that would be great.

I get that. There are things that I like doing the hard way. Like when out boondocking I use a radio to send email instead of just wafting until I have cell service. And I have been fooling around with component level electronics for over 40 years. I guess for me a power system is something I just want to work when I am in the middle of nowhere.

But point taken and enjoy!
 
Welcome to the forum.

You can't connect the same set of panels to multiple charge controllers.

You seem to be making this more complicated than is necessary. Since you haven't given additional information on "a particular battery chemistry," I'm going to ignore it.

12V panels connected to MPPT connected to 12V battery. 12V inverter connected to 12V battery.
Fridge runs off 12V battery.
All other devices run off "big" inverter sized for the chainsaw OR
Chainsaw run off "big" inverter and chargers run off smaller inverter sized for chargers.
"Big" inverter powered off when not needed to avoid idle power consumption.

Done.
Here are the batteries that I'm including in my planning:

Qty 1* - 48V 556Wh LiIon e-bike battery (want to get a backup soon)
Qty 2 - 12V 120Wh LiFPo batteries for jack compartment of SUV (may buy more depending on heat loss from fridge)
Qty 1* - 12V 506Wh SLA batteries for running power tools (will buy additional when I get a tool trailer)
Qty 3 - 18V NiMH Porter Cable cordless tool batteries.

Currently, none of these charging loads is sufficient to use all of the power available.

Under most circumstances I want the following priorities:

1. Keep the fridge running and the LiFPo charged up first.
2. Charge the cordless tool batteries
2. Charge the e-bike battery if there is power available and it needs to be charged.
3. Charge the SLA battery if it is present and needs charging.

The system you are proposing would take power from the LiIon batteries to charge the e-bike battery if the panels are shaded or its at the end of the day. But, I've got a Powertail that could shut off the e-bike battery charger's 120 VAC programmatically. Its not clear to me how to deal with charging two banks of 12V batteries (LiFPo and SLA).
 
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What about using my Victron MPPT 100/30 to charge the e-bike battery, and then hooking up my Victron MPPT 75/10's PV input to the load on the 100/30? The MPPT 75/10 is going to see an almost constant voltage, regardless of its current draw. So off the top of my head it doesn't seem like there would be any instabilities with this configuration, albeit it is an off-the-label configuration.
 
Might work. MPPT 75/10 would only be powered when the 48V battery is powering the 100/30. Victron MPPT must have batteries connected to function. Disconnect the 48V battery, the 75/10 goes offline.
 
Might work. MPPT 75/10 would only be powered when the 48V battery is powering the 100/30. Victron MPPT must have batteries connected to function. Disconnect the 48V battery, the 75/10 goes offline.
Oops - my nominal 48v MPPT is a Victron 100/20, not a 100/30.

Actually, the manual says that it continues to function with either PV or a battery. I've got first hand experience with this, because this is how I reprogrammed the 100/20 from 12V to 52V. (I redid my physical layout before I changed the Victron settings, so the 100/20 could no longer connect to the 12v LiFPo batteries. But I plugged in the PV and then connected from my Android phone, and changed its charging profile without a battery connected.) But in my last experiment, the 100/20 couldn't see the battery. I didn't realize the Bafang battery had an On/Off button! I guess I need to retry that experiment this afternoon!

In the short term, I'll need to swap a couple of XT90 connectors, and make up a jumper that goes from the 100/30 load terminals to XT90.

In the longer term, I'll need a multipole switch with XT90 connectors that direct the PV to one or the other MPPT's, and that simultaneously takes the 75/10 PV from the switch or the 100/30's load.

But this only needs to happen when I start or end an e-bike ride. Which isn't going to happen until I actually assemble the e-bike kit!

I should probably do these experiments now, in the heat of the day. Working on mounting the panels on my SUV's roof in 96F is not at all pleasant
 
Please link or copy/paste that information. I am 99.99% certain it is not correct, or you have misinterpreted it, and it will not function as you desire.
 
Please link or copy/paste that information. I am 99.99% certain it is not correct, or you have misinterpreted it, and it will not function as you desire.
The 100/20 starts up as indicated by being able to connect to it with my Android phone, but it seems that it won't pass current from the PV to the load without a battery connected. However, there is something screwy happening on the 75/10. So I'm not sure if this is the case.

So far I'm not getting the 75/10 to power the refrigerator from the PV. The PV is showing 36V when connected to the panels and 58v when connected to the 100/20. In both test cases there was no current coming from the PV. The power for the refrigerator is coming from the battery, which show up as being absorption mode. I've had this configuration working previously, so I'm really confused. Why discharge the battery instead of using the PV???
 
Please link or copy/paste that information. I am 99.99% certain it is not correct, or you have misinterpreted it, and it will not function as you desire.
6.1. Start up The solar charger will power up as soon as it has been connected to a battery and/or to a solar panel. As soon as the solar charger has been powered up, it can communicate via the VE.Direct port and Bluetooth. The the solar charger's data can be read out and setting configurations can be made using the VictronConnect or the optional display. The solar charger will commence battery charging as soon as the PV voltage is 5V higher than the battery voltage. For charging to continue, the PV voltage must remain at least 1V higher than the battery voltage.
 
6.1. Start up The solar charger will power up as soon as it has been connected to a battery and/or to a solar panel. As soon as the solar charger has been powered up, it can communicate via the VE.Direct port and Bluetooth. The the solar charger's data can be read out and setting configurations can be made using the VictronConnect or the optional display. The solar charger will commence battery charging as soon as the PV voltage is 5V higher than the battery voltage. For charging to continue, the PV voltage must remain at least 1V higher than the battery voltage.
Note that it doesn't say anything about the load, and whether that works without the battery connected.
 
All that says it that it will start up from either source and can be configured. It does not state or imply that it will function on solar only.

I did find reference on the Victron community forum that they can function on solar only, but the load has to be very consistent such as a simple resistive load (light bulbs). I highly doubt the 75/10 hunting for optimal power would qualify as a simple resistive load.
 
you could build a small super cap bank, use single MPPT to charge it, then use dc dc converters to regulate the bank to 12.0V for appliances

if you want a separate battery, the supercap bank can power a dcdc battery charger.

just throwing ideas out there
 
All that says it that it will start up from either source and can be configured. It does not state or imply that it will function on solar only.

I did find reference on the Victron community forum that they can function on solar only, but the load has to be very consistent such as a simple resistive load (light bulbs). I highly doubt the 75/10 hunting for optimal power would qualify as a simple resistive load.
Probably using the 75/10 to charge batteries would be fairly consistent. But the refrigerator compressor kicking on and off could cause problems.

In any case, that's not a scenario that I'm anticipating. Now that I understand that the 100/20 doesn't have an intrinsic buck boost converter, so it won't work with my panels to charge the 52v battery. I've ordered a 300W inverter for the car setup, and will use the 2 amp charger for the e-bike battery.
 
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