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PeterS

Connecting load and battery on a solatr controller

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PeterS

Hi,

 

Apologies if this is a really basic question, and if here are answers elsewhere please direct me to them.

 

I am having trouble understanding the correct/best way to connect a load and battery to a solar controller.  The setup i am working on is a very simple one for a van conversion.  It consists of a 200w solar panel, a 40a mppt controller and 2x130ah batteries in parallel. The controller is a standard 3-stage model (contant current, constant voltage, float).  The load will consist of LED lights (5A), water pump (10A), Fridge (15A), toilet (5A), 12v sockets (30A), 800w inverter (80A).  The values in brackets are the fuse rating installed on each load, not the constant current draw, which will likely be 5-10A max at any one time.  Currently all load is connected to the battery terminals.  I am aware that the inverter must be directly connected to the battery.

 

I was wondering if it is necessary, or just better, to connect the other loads to the controller load terminals rather than the battery?

 

Without load, in the constant current mode it would be assumed that all output from the controller is drawn by the battery. With load, it would not matter if the load were connected to the battery or controller as all possible power would be available on the battery connection. Is this correct?

 

In constant voltage and float mode only a small current may be required, so can the controller supply the excess current to the load terminals? If the load is placed on the battery then will the charge current be diverted to the load, with current drawn from the battery as necessary, until the battery voltage drops enough to cause the controller to enter constant current mode?

 

What if the load requirements are greater than the controller can supply, when the load is on the controller load terminals? Will the charge direction be reversed so the battery supplies the controller's load terminals?

 

Many thanks for taking the time to read.

 

Regards,

 

 

Peter

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binky

as far as I'm aware you don't direct connect any load to the battery

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PeterS

Hi binky,

 

Thanks for the reply.  What do you mean?

 

Of course, I have isolating switches and fuses between battery and all loads, pv into the controller, batt out from controller etc, if that's what you mean.

 

Regards,

 

 

Peter

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Geoff1946

On a similar job done by my son and myself we installed a pair of busbars, (actually re-purposed earth terminal blocks), to bring together two leisure batteries, the van charge supply, and the solar controller output, and of course the fuses for the various loads.  It seems to work fine like that.

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binky
1 hour ago, PeterS said:

Hi binky,

 

Thanks for the reply.  What do you mean?

 

Of course, I have isolating switches and fuses between battery and all loads, pv into the controller, batt out from controller etc, if that's what you mean.

 

Regards,

 

 

Peter

Pretty much! 

 

What Solar control do you have?

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PeterS

@binky I have this one https://www.ebay.co.uk/itm/eSmart-3-Series-MPPT-Solar-Charge-Controller-40A-DC-12V-24-36-48V-UK-SHIP/163109008143

which seems to be a similar model and functionality to the Tracer AN ones.

 

@Geoff1946 That is how i have rigged things up, all negatives are wired to a common bus bar, the battery positives run via switches to a charging bus bar and a load bus bar.  The split charge relay, direct to vehicle battery cable (for charging the vehicle battery from solar), solar controller and battery charger are also connected to the charge bus bar.

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PeterS

I was just confused as to whether the load should be on the solar (or in my case switchable between solar and load bus bar).

 

This doesn't answer how the controller manages current supply to the load and battery.  When it's outputting to the battery at reduced current (float) will the excess solar power be available on the load?  If the load requirements exceed what the controller can provide from solar does this draw from the battery via the controller?  Or does the load simply stop working?

 

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Geoff1946

Based on the one and only system I have experience of, I believe the solar controller works on the voltage it sees at its output terminals.

If it's around 14.4 volts, i.e. fully charged battery with no load, then it will go to trickle charge/float mode. If the voltage is lower, either because the battery is not fully charged or because current is being drawn by an external load, then the controller will increase its output.

The solar controller doesn't, "know", where its output is going.

It's exactly the same as your car alternator. Switch on the headlights with the engine off and the lights draw from the battery. Now start the engine and the lights will go brighter as the alternator increases the voltage; some of the current is supplying the lights, the rest is recharging the battery. The alternator doesn't know where its output is going.  Does that help?

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binky

Like the Union jacks, that looks like a Goodwe unit - Chinese, could be wrong. Victron would be my controller of choice for this sort of project.

 

OK so a becent battery controller is only looking at the battery and potential energy supply from your panel, it doesn't give a hoot about the loading. I've not looked at such things for a while, but you could connect a grid charger to the same battery, so when you plug into the mains it also charges the battery. 

 

BBL batteries are a good source of info and parts.

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PeterS

@Geoff1946 Thanks Geoff, I understand what you're saying, but it doesn't really clarify my understanding of how the controller operates.  From what you're saying the controllers may as well not have load output at all.

@binky And thanks binky, you seem to be saying the same, again that the load is virtually irrelevant.  If the controller turns out to be ineffective i'll switch to a reputable brand.

 

It doesn't quite add up, as the controller potentially has the ability to output different voltages and currents to load and battery.  I'll just leave things as they are for now i guess.

 

As an aside, i've been charging 2 Leoch 130AH adventurer batteries with the solar.  They arrived at 13.1V and have charged to the 13.8v.  When i turn off the solar the vltage drops to 13.3V after a while.  Is that normal?

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Geoff1946

Ah, so I'm guessing your controller has separate battery and load terminals(?). Mine doesn't. As I described, with my son's system everything is connected together at a common busbar.  I wouldn't be surprised if the terminals of yours are just connected together inside it. If not, then only the controller maker can tell you how it works.

 

That 13.8 volts is a tad low for a fully charged lead acid. (Again a guess that's what your "adventurer" batteries are; anything else then consult the battery maker's data). 

A full lead acid charge is above 14 but not exceeding 14.4. Above that would cause overcharging,  and possibly damage and loss of electrolyte, so at least you are on the safe side with 13.8.  You may also find that left longer it would creep up on a reduced charge rate.

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binky

as I said I'm not familiar with that unit, but the different voltages will relate to different battery configurations, most car / leaisure batteries are 12-14V, but if you wire 2 batteries in series it doubles the voltage, if you wire in parrallel the voltage stays the same . It's quite popular to use higher voltages such as 48V for the batteries, as this reduces the ampage, so you can use smaller cables, and is more efficient when running through an inverter. that steps voltages up to say 240V.

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PeterS

Thanks again guys.  The batteries are AGM (the data sheet here https://www.alpha-batteries.co.uk/media/catalog/product/l/a/lagm-130.pdf).  It says the initial charge for cycling can be set to run at 14.4-15v then standby charging at 13.5-13.8v.  The graph at the bottom is a bit confusing, but i think it says a standard charge voltage of 14.1, with boost of 14.4, and a max of 14.7v.  The charger has the following profiles for the constant current (bulk) charge (lead = 14.6v, sealed = 14.4v, gel=14.2v) then drops to 13.8 for constant voltage/float for all 3, so think maybe any would be okay, though let know if you think a profile is best.  The charger also applies an extra 0.2v over the bulk charge voltage for 60min per month.

 

I chose two separate batteries over the larger one as the discharge profile was slightly better for these batteries when half the current was required.  A 24v or 48v system would be ore efficient i guess but all the appliances (toilet, fridge, lights) are 12v (didn't know other voltage systems were possible really).  i'll maybe do a refit in the future, when it's time to change the batteries, and check the compatability of the appliances in the meantime.

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binky

stick with 12v then!  If the unit has load connections then it may provide a stabilised 12V output to connect loads to? 

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PeterS

Thanks binky, will give it a blast.

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