Victron SmartShunt

[ShedPower]

What do you think about this?

https://rvnerds.com/2017/08/07/electrical-myths-part-3-mixing-batteries-different-agescapacities/

[SunEagle]

Yeah they are new batteries. Ive just ordered another one. I also have a 100ah battery kicking around. I have read that if your batteries are in paralell then you can add a battery with a different amp hour rating. Only true for paralell, not in series. if this is the case, ill also add the 100ah.

Two things you need to look into.

First parallel wired batteries can cause one or more to fail before the others.

Second. It is never a good idea to have different batteries in the same system. One of them will end up doing most of the work and fail early.

The best idea is to either use Lithium type or have the correct amount of FLA type in your system. Also with FLA you will need charging amps equal to about 1/10th the battery system Amp hour rating. More then 1/8th of the AH rating and you run the risk of cooking your batteries. Less than 1/12th of the AH rating and you run the risk of sulfating the batteries. And finally adding new batteries to older ones will hurt the newer ones.

[ShedPower]

Yeah they are new batteries. Ive just ordered another one. I also have a 100ah battery kicking around. I have read that if your batteries are in paralell then you can add a battery with a different amp hour rating. Only true for paralell, not in series. if this is the case, ill also add the 100ah.

[chrisski]

Now that you can get an idea how much your batteries can put out ampwise, you can figure how many batteries to add to it. Barring for weather, your highest output will be in mid June. For my Rv, that makes a huge difference at noon with the sun straight up in the air shining on all panels as compared to December on the shortest days of the year when the sun is much lower and some of the panels are always shaded.

There’s mixed recommendations about adding lead acid batteries later about how the new ones can get dragged down to the older set and having to replace them at once. If these batteries you have are new, now is the time to add more. It’s always best to design the lead acid system to your power needs because of having to replace batteries. Lithium is a bit easier to add to and is coming down in price for pre-made batteries.

[ShedPower]

The main reason for having the system is to enjoy doing it. I don't need it as such, but to have our freezer on solar is satisfying.

[ShedPower]

Wow! I think I need to increase the load and add a couple of batteries. I have limited the chargers to 40 amps between them for now.

[chrisski]

My guess is since you need about 62.5 ah of power a day, assuming 750wh, you will be close to the 39 amp max when your batteries are full. Watching for a cycle or two will help.

The problem would be when it’s cloudy until noon and then suddenly sunny. 1,5 kw of panels could get 90-100 amps of charging amps to a battery. I had about that many panels and because of angles to sun panel shading, the mist I saw was 74 amps, which still exceeded my 60 amp limit.

[ShedPower]

Thanks. I would like Lithium but I’ve spent a lot on this system so far so will have to wait for a lithium upgrade. I think I may now be in the same position you had. With 1.5kw solar panels my 3 batteries should charge quickly, depending on load of course. The load currently is 750w a day.

[chrisski]

I had three Victron SCCs charging a lead acid bank, and limiting max charging amps was a problem. For me, I did not deplete my batteries more than 25%, so they were charged before the sun hit high enough in the sky to exceed the max charging amps.

I thought about entering a max amps into my SCCs that when added up never exceeded the max charge rate, but each SCC charges different so that would be inefficient.

I did not realize the Cerbo would allow an entry for all three to max out at.I know my 3 SCCs only have one entry each

Id recommend 10% as mentioned unless the spec sheet says different. My FLA spec sheet was13% but a gel or AGM may be 33%.

I ended up installing a lithium bank and am much happier.

[Bala]

As far as expenses, it depends on why you have thus system when you have mains power.

it is possible to run multiple controllers How well they play together depends on tge settings available.

[ShedPower]

Thanks, 10%, thats helpful. So about 39 amps max. I have an automatic transfer switch that switches back to mains power when battery voltage reaches 12.2, or whatever it is set to.

What im wrestling with is having two charge controllers on the same system both independently pumping amps into the batteries. They are victron, so I could get get a Cerbo GX which would supervise the overall current going into the batteries, but I am spending way too much on this system at the moment!

[Bala]

Generally around 10% of battery capacity for charge amps.

For off grid systems a generator and charger are used for extended overcast weather. You have mans power so you could just get a charger and plug it in.

[ShedPower]

A battery question on this system. I have 3 x 130ah lead acid leisure batteries in parallel. I have 360w panels on my shed roof but while its overcast they are struggling to charge the batteries. Two days and still not fully charged. So tomorrow I am buying some larger panels, 3 x 410w panels. The new panels will have their own Victron charge controller because of bigger volts and amps.

My question is, how many amps could, in general, 3 lead acid batteries in parallel cope with when charging? The most I have had out of the 360w panels when its sunny is 15 amps. With the new panels, im guessing there would be (from all panels) about 30-40 amps. I don't want to fry the batteries! I have had no success trying to get any information from the ebayer I bought them from and the batteries have no brand names on them. Thanks.

[ShedPower]

That’s very reassuring! Thanks.

[jflorey2]

Thanks. I am confused though how the batteries can be 99% full and now be 12.4v. It doesn't seem possible, does it?

If you fully charge a lead-acid and then put a moderate load on it you will see about 12.4V.