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Why is the load connected directly to the battery terminals?

Jotunn

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Jun 22, 2020
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Looking at the basic small scale solar designs on Will’s Mobile Solar Power website, how does the low voltage disconnect (LVD) that is built into solar charge controllers work to protect the batteries from being discharged too low if the electrical load is not connected to the “LOAD” terminals?
The electrical load (and batteries) appears to be connected directly to the “BATTERY” terminals, therefore potentially (???) bypassing the LVD circuit built into solar charge controllers.
 
Lithium battery? The BMS would step in and disconnect the load if so.
 
No, I’m just using standard static deep cycle batteries but Will’s designs do seem to feature his favourite Lithium batteries. The Lithium batteries have their own low voltage protection built into them then?
 
Just checking Will’s designs here - https://www.mobile-solarpower.com/, they don’t specify that a Lithium battery must be used, only recommended for their greater depth of discharge and longer lifespan as being a more economical option in the longer term.
The parts lists show lead acid based batteries as options.
 
Yes, lithium batteries have their own built in protection. Can you post a link to the design you are talking about?
 
There isn't specific protection built into those systems. The inverter would likely have low voltage shutdown built in. The separate 12V loads would not be disconnected unless the user takes action when using a lead acid battery.

The charge controller does have a load output terminal, if the 12v load is within the ratings of that output it could be connected to that (the inverter must remain direct to battery) and that would then be able to disconnect them on low battery voltage. If the 12v load draws more amps than the controller's output is rated for, a relay could be connected to the load output terminals, and that in turn control the 12v load.
 
There isn't specific protection built into those systems. The inverter would likely have low voltage shutdown built in. The separate 12V loads would not be disconnected unless the user takes action when using a lead acid battery.

The charge controller does have a load output terminal, if the 12v load is within the ratings of that output it could be connected to that (the inverter must remain direct to battery) and that would then be able to disconnect them on low battery voltage. If the 12v load draws more amps than the controller's output is rated for, a relay could be connected to the load output terminals, and that in turn control the 12v load.
Pretty much all solar charge controllers that I’ve seen in stores and for sale on the internet have a low voltage disconnect (LVD) circuit built into them, so I’m puzzled as to why the DC electrical load is not connected in some way to the “LOAD” terminals as this is how they appear to be designed and used for the LVD to actually monitor the voltage properly and then activate to disconnect the battery in a very low voltage situation.
I could be wrong though and it might be adequate for everything to be directly connected to the “BATTERY” terminals and the LVD feature will still work but that is why I’m seeking advice.
For background though, I’ve basically replicated the wiring setup of this design - https://www.mobile-solarpower.com/the-minimalist-great-for-small-vans-and-cars.html, that is available on the Mobile Solar Power website to install a system for a small off grid cabin but using a much cheaper PWM solar charge controller (commonly seen on eBay very cheap with black plastic rectangular body and blue face with LCD readout) and using two deep cycle batteries but the solar system at the cabin was over-utilised by some people who stayed in the cabin for a long stay and the LVD feature never activated to protect the batteries and the battery voltage dropped to below 10 Volts.
So, I’m not sure at this point whether the system is such that the LVD has been effectively bypassed due to the way it is wired up and that is a bit of a design flaw or whether the super cheap PVM controller is faulty but that’s why I’m seeking advice here. If the system is wired correctly and such that the LVD is not bypassed then it could be that the cheap controller is faulty and the inbuilt LVD is not working.
 
The SCC's LVD feature will only work for things connected to it, or via a relay connected to it. It would be possible to rejig things to get the SCC's LVD feature to disconnect the small DC loads for the plan you justed linked, but it would mean quite a few changes to that particular layout as the SCC's output is being passed through the fuseblock to get to the battery.

LVD has been bypassed.
 
The SCC's LVD feature will only work for things connected to it, or via a relay connected to it. It would be possible to rejig things to get the SCC's LVD feature to disconnect the small DC loads for the plan you justed linked, but it would mean quite a few changes to that particular layout as the SCC's output is being passed through the fuseblock to get to the battery.

LVD has been bypassed.
OK, thanks for the response.
I’ve contacted a number of SCC retailers and of the few responses that I’ve had so far they are saying the same, that by not using the LOAD terminals to provide DC power output then the LVD is bypassed.
I guess it just makes sense really that the power would be cut to the LOAD terminals to stop the batteries being drained too low but still have the battery connected to the solar power input to top up the batteries again.
I thought that maybe the LVD circuit was connected at the BATTERY terminals to cut power from the batteries because this is the way it’s set up in the designs at the Mobile Solar Power website and because it did not make sense to me to exclude the LVD being able to activate in any system design but it does appear that the design is flawed in that way.
If a LVD circuit cut the power at the BATTERY terminals themselves then that would mean that the battery is also cutoff from solar power input and there would be no way to top up the battery to then get the LVD to reconnect since the battery voltage would not go up again and the LVD reconnect would not work.
 
I have a few relays laying around, I'll make a relay LVD from the SCC load output and test it.
 

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Using my system as an example, A 12V relay powered by the SCC load output would shut off at 11.1V .

Now the rub. The SCC output has to be on at all times, the relay will have a constant current draw, and the biggest issue is where to put it.

For my design I could put it between the fuse box and shunt on the negative side. This would cut off all loads but still let the SCC charge the battery.

Now you would have to have a relay big enough to hold your entire load and terminals that are able to attach the size wire you are using.
 

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If you set it up like the link you posted you could make an easy SSR LVD powered from your SCC output. It would be an easy modification to your setup and not cost much at all.
 
If you set it up like the link you posted you could make an easy SSR LVD powered from your SCC output. It would be an easy modification to your setup and not cost much at all.
Thanks for your proposed solution but I’ve already stripped out the entire system due to a disagreement with the owners of the cabin and won’t be building any more systems of that design.
I intend to make my own system design ensuring that the DC electrical load is connected to the LOAD terminals and I have a light truck that I will install the retrieved solar system into. It’s not that hard to modify the system so that it is wired correctly and just by adding a bussbar for the battery and inverter connections and having the DC fuse block wired direct to the LOAD terminals.
 
Pretty much all solar charge controllers that I’ve seen in stores and for sale on the internet have a low voltage disconnect (LVD) circuit built into them, so I’m puzzled as to why the DC electrical load is not connected in some way to the “LOAD” terminals as this is how they appear to be designed and used for the LVD to actually monitor the voltage properly and then activate to disconnect the battery in a very low voltage situation.
I could be wrong though and it might be adequate for everything to be directly connected to the “BATTERY” terminals and the LVD feature will still work but that is why I’m seeking advice.
For background though, I’ve basically replicated the wiring setup of this design - https://www.mobile-solarpower.com/the-minimalist-great-for-small-vans-and-cars.html, that is available on the Mobile Solar Power website to install a system for a small off grid cabin but using a much cheaper PWM solar charge controller (commonly seen on eBay very cheap with black plastic rectangular body and blue face with LCD readout) and using two deep cycle batteries but the solar system at the cabin was over-utilised by some people who stayed in the cabin for a long stay and the LVD feature never activated to protect the batteries and the battery voltage dropped to below 10 Volts.
So, I’m not sure at this point whether the system is such that the LVD has been effectively bypassed due to the way it is wired up and that is a bit of a design flaw or whether the super cheap PVM controller is faulty but that’s why I’m seeking advice here. If the system is wired correctly and such that the LVD is not bypassed then it could be that the cheap controller is faulty and the inbuilt LVD is not working.
That load is usually limited to around 5 Amps and not suitable for large loads. It could be used to control a relay that could cut off inverter during a LVD event. They also sometimes shut down when there is no sun. So check specs of all SCC
 
That load is usually limited to around 5 Amps and not suitable for large loads. It could be used to control a relay that could cut off inverter during a LVD event. They also sometimes shut down when there is no sun. So check specs of all SCC
OK, thanks.
I’ve looked at specs on websites for SCC retailers and manufacturers but all I‘ve seen so far in their specs in relation to the LVD and LOAD terminals is the preset LVD cutoff and whether that LVD cutoff can be changed or not. I haven’t seen what amperage load the LOAD circuit is capable of but will look again. Maybe it’s in the manuals for the SCCs, so I’ll look more closely at the webpages and download any available manuals.
I’m only setting up for low consumption from the LOAD terminals such as LED lights and charging phones, tablets and other small devices. The inverter is what I’ve decided is to be used for higher loads connected direct to battery/s but I notice that most are a fixed and quite low LVD that can’t be changed. The default LVD settings appear to be very low and low enough to possibly damage batteries at around 10.5 Volts but I don’t have much experience, so not sure on that. I would have thought that an LVD set at 11 to 11.5 Volts would be safer for long battery life.
 
My Epevers LVD is 11.1V and I think it can be adjusted if you set the battery to user.
 
You are stuck on using the charge controller’s switched output. This fixation is keeping you from understanding the problem imho

you can adjust most charge controller’s switched output voltage to whatever you want to. Use that with a relay to disconnect your fuse panel feed when voltage goes low. If the ‘constant energy drain’ of the relay bothers you, add another 100W of panel and another 100Ah of battery storage.
 
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