Solar set-up Advice

[JF117]

Hi,

Planning on using my Bongo prettymuch all summer this year and will be spending a bit of time off-grid so wanted to explore some solar options.

I have done some research online with different youtube videos and so far I understand that I’ll need a panel and a solar charge controller. Was thinking about a Victron SmartSolar MPPT but open to more suitable suggestions too.

Anyway, where my understanding lacks is what is missing beyond this? Is it these two items and some wire straight to the LB?

To the best of my knowledge my current set up is SB / LB where the LB is able to get a trickle charge off the SB via a Switch Charge Relay when the engine is running. Directly connected to the LB, I have a waeco perfect power 1000w inverter and an eberspacher diesel heater, both operated by their respective on/off switches.

Additionally to this I have EHU and a breakerbox where, as far as Im aware, when I connect the EHU the set up/ board flips to the EHU and draws power from there instead.

Question is, if I get a panel and the solar charge controller, do I just run wire straight to my LB’s positive and negative respectively and that is it? Could I be sending too many volts to the LB if both my engine is running and solar panel operating?

Should it therefore be going to the SB instead for example since the SB has a relay between it and the LB? This way the SB is getting flow from either the alternator and or solar and when good volts are flowing through the SB, it will in turn flow to the LB? Or could I end up cooking the SB too?

Understandably these might be a silly questions but please enlighten me as to what could or should come between the solar panel controller and my LB.

Thanks for your help!

[g8dhe]

Yes you can wire direct to the LB, that's what the controller handles, it can also have other power sources charging the battery as well, in my case the EHU Charger and a Split Charge Relay all three sources are in parallel and which ever one has adequate power will provide the power.

I hope you don't plan on using the Inverter much, they are usually very inefficient and can drain a LB in no time at all!

[JF117]

Yes you can wire direct to the LB, that's what the controller handles, it can also have other power sources charging the battery as well, in my case the EHU Charger and a Split Charge Relay all three sources are in parallel and which ever one has adequate power will provide the power.

I hope you don't plan on using the Inverter much, they are usually very inefficient and can drain a LB in no time at all!

Thanks for that insight.

Think we have referred to this in another post where I was exploring my system.

Since the fridge is connected to a three pin outlet having the inverter on or the EHU connected are the only two ways in which the fridge can be on.

We usually have it running when the engine is running and turn it on and off (fridge stays cool enough) when completely static and no EHU. Im hoping the assumption is that when the engine is running its providing enough charge to the LB to offset the drain via the inverter and to be fair it seems to have worked, unless Im massively mistaken and you are about to tell me different lol..

Then, after that, if we’re sitting static for long periods I will turn the engine on and tick it over every so often.

It is the way the system came and Im not sure on what other way to do it.

However, back to topic, do you have anything between your solar power controller and your leisure battery?

I understand that the SPC/MPPT will regulate the charge to the LB and the SCR allows its circuit to flow when the engine is running therefore transferring charge from the SB to the LB. However, when it its all happening simultaneously and since there is nothing between the MPPT and SCR (they're not connected or talking to eachother), wont that run the risk of over charging the LB?

I tried to ask Chat GPT the same.. lol and it kept getting confused and changing advice, it dld however mention a dual charge controller where essentially, the MPPT would be connected to the dual charge controller and in turn that would be connected to the SB and LB whilst retaining the SCR between the SB and LB.

Does this make any sense though?

The replies weren't really all too consistent though and I think its because it was under the assumption my LB was taking charge directly from the alternator and not via the SCR.

For clarity, if following your advice / set up, is the understanding that if the engine is running and the solar is running that it will each send charge together o the LB charging it faster then when the LB is sufficient charge each unit; both the MPPT and SCR will close their circuits off to avoid over charging?

Is there such thing as sending too much current to the LB though?

Thanks

[g8dhe]

Yup if the fridge isn't a 12v compressor then not a lot of options!

The SCR will normally only operate when driving and the alternator is charging the SB, the voltage then rises over the trigger voltage and operates to allow the charging of the LB in parallel with the SB. When neither battery voltage is above the trigger voltage (around 13.6 volts) the relay releases and the batteries operate independently.

The controllers/regulators won't allow the voltage across the batteries to exceed the maximum for charging, they simply reduce the amount of current they contribute to the overall charging so neither battery at any time will be overcharged.

[JF117]

The controllers/regulators won't allow the voltage across the batteries to exceed the maximum for charging, they simply reduce the amount of current they contribute to the overall charging so neither battery at any time will be overcharged.

How can the MPPT know how much current or voltage thats coming independently from the SB via the SCR if only connected to the LB directly?

Is it a case that it will know because the LB will have reached a certain voltage and the MPPT will switch off / regulate itself in which case, at least for a period of time, it could be receiving quite a bit of current (from both the engine and solar panel) until it reaches that point and that is how it regulates it?


Sorry if it sounds like Im repeating myself, essentially just want to make sure that if I connect a solar panel to my LB via MPPT that I wont fry it under the current set up (SB and SCR).

[g8dhe]

The voltage along any conductor is essentially the same at any point.
So when different power sources are connected in parallel, to in this case the battery system, all the sources see the same voltage.
Each source is setup to regulate the voltage at a given level, the current it then supplies depends on the resistance that the load (the batteries in this case) offers in conjunction with any internal voltage (battery terminal voltage) offset.
So basically each source will attempt to supply current into the system until it exceeds its regulated voltage, at which point it stops supplying power.
In the situation when there is a Split Charge Relay and it is operated then both batteries receive charging from whatever source is supplying current up to its regulated voltage.

As you say in the next paragraph, the whole system functions by monitoring the voltage along the common charging and load connection wire, so it doesn't matter what other sources are doing they all work by checking the voltage and contributing current to meet the demand until the voltage reaches the set-point for each source. Now this is where "clever" or "intelligent" chargers are really no more than Marketing words - they don't actually know where there current has gone and assume its into the "battery" whilst in reality there may be more than one battery and also other loads, lights, phone chargers, radios etc. all using the power hence never pay more for the Marketing words, just choose chargers that are regulated ones!

If you want more info happy to supply but not sure that this is the right medium, it really needs diagrams and a little maths to explain all the possibilities but be assured that your batteries won't come to harm when any or all of the possible power sources - Alternator, EHU Charger, Solar controller, even when there is a SCR in the system - are operating nor when any of the sources is switched off either.