I’m planning to build an offgrid system using the Inverter RS Smart Solar, and I’m in the process of deciding between 15s or 16s lithium battery. But I find confusing info regarding the max charge voltages:
In the latest users manual it says max float 60v, max 62v equalization, over-voltage disconnect: 65,5 V.
If I create a demo product in the victron app, I can set up 69.56v for bulk / float / equalization, which is wildly different from the manual…
With either 15S or 16S, you’ll be OK, considering their voltage settings.
Maximum 52.5V (15S) and 56V (16S), taking into consideration a float voltage of 3.5V per cell.
But, in general, don’t ever use any setting that will rise the voltage over 62V !!!
The electrolitic capacitors on the battery input of the RS range of products are rated for 63V !
That 65.5V from the docs, in my opinion, has no place to be there.
Also, as a side comment and educated choice, when the voltage is closing so much to the limit of one component, the designer should choose the next level, in order to honor the reliability. In this case, the capacitors should be 80V rated.
But I suppose that only the lead-acid batteries, with their equalization voltages, are coming closer to 63V and they are not so largely used anymore, so the 63V rating capacitors were chosen from an economic stand point.
The voltage limit is only a problem if you have some lead acid batteries.
The RS is designed for lithium. Unless you have created an unconventional lithium battery bank it wont be an issue.
Won’t be equalising lithium either. So also a non issue.
Pretty please, care to elaborate a little?
One would say, seeing the words “absorption”, “float” and the default voltages of 57.6V (2.4/cell) and 55.2V (2.3/cell) that was designed for lead-acid…
The market is moving there. The RS is off grid. Lead acids do not cycle well.
Most lead acids equalize close to the 16s lithiums anyway so it is usually fine.
Going higher in voltage then technically means it can’t be installed in homes as there is a voltage limit to be in low voltage application category.
There are a few lead acids that need higher like the Rolls. (List obviously not comprehensive) But even AGM uses lower and not usually equalised. In all honesty unless it is niche will not need higher than that. As you said - not out of application range.
For Lithium-Ion cells the recc. upper limit is 4.0V, so for 16s you need 64v for a full charge. At 60v with 16s it would charge only to 3.75v, which means wasted battery capacity.
For the 60v the ideal Li-ion configuration would be the 15s (15x4.0 = 60). So this is what I will build.
Absolutely agree…
Thanks, this is what I will do. It means there is a bug in the app, I also tested with other demo products and it allows with all of them to set 69.56v, so this is something for the software team to look into. As an end user I expect to see realistic parameters in the demo products.
In the users manual it is stated you can use lead acid, actually the default battery configuration in the app for all Victron products is for lead acid.
There is very little usable capacity in the upper voltage range of a lithium cell, if you configure a system to run that high, it is not going to last.
There is a reason manufacturers keep them around the 3.5V range.
Yeah. Cycling lead acid… I guess there some are die hards there that still have to be catered for.
Are you using lipos as in 18650s or something on those lines? Only reason why i could think you would go to 4.0v.
See that those voltages you’ve poster are for Li-Ion batteries.
We are talking about LiFePO4 technology, much more recommended and used.
For sure you’ve though of LiFePO4 batteries, because the others you won’t find them in 15S or 16S configuration.
Or am I wrong ?.. You did mention 15S or 16S…
Why do you think this? Most electric vehicles actually use Liion cells. For my case, I build a 20kW pack using Kia Niro modules, which are 200A 4s Liion…
They are perfect for building a 16s pack (or 15s if I leave the last cell unused)
In our motorhome I built in 4 tesla Liion modules (7s, 110A), they are already 7 years old and still have about 75% of the nominal capacity.
Charging them up to 4.0v and discharged to 3.3v, using them 8-10 months a year, since 4 years…
Because the inverter is a 48V inverter.
4V type cells are used in a 13S or 14S configuration, not 15-16…
16 * 3.7 = 59.2 for idle and 16 * 4.2 = 67.2 for 100% SOC is way out of those inverters range.
Li Ion is an abused term, it can cover a somewhat wide range of chemistries with different requirements. A battery is a collection of cells, usually with some form of management, the manufacturers recommendations is what should be used for charging.
Getting it wrong can have dire consequences.
@Wanek if you need higher voltage for charging from solar look more into the 250 range of MPPT. You can use the RS still there is an inverter only option of the unit if you are keen on their high efficiency (as in it has no built in mppt).
If you are building your own pack look at the datasheet for the specific cells you have. That Battery university article is too general.
…48 v inverter, which under 52v is unable to provide the nominal output according to the datasheet. So, yes, it is possible to use with 13s, but you will never get to 52v, so it will never provide the nominal output of 5300w.
Even with a 14s pack, will be above the 52v limit only for a very short SOC.
So, the only option to use most of the time on the “correct” voltage (>52v), is using 15s or higher… Otherwise you pay for a 5300w inverter and you will use a 4800w
In my logic, if I use a 15s pack, with 60v it will be charged exactly on the correct 4.0v/cell, and most of the time the battery will sit above the 52v limit. With discharged battery will have around 49v, which is great.
Using higher voltages I consider generally more practical, because of less losses on the wires and the inverters can also work a bit more efficiently, meaning less heat, fan noise, etc. I didn’t know about the 63V input capacitor limits, it is a pity they made this decision.
Exactly. I choose this specific 7s battery from Tesla, which is pretty rare, they made it for Merc C class, if i remember correctly.
Our camper is a Merc Vario, it has 24v alternator (nominally), which gives around 28.4v. This way, I could connect the solar batteries and the starter batteries together, because the alternator can never overcharge the Tesla modules (it charges up to 4.05v / cell, which is perfect).
Of course, I used a 300w resistor between the starter batteries and tesla, to limit the current to 50A, not to fry the alternator It works perfectly since 4 years. This way the solar panels of thr rv also charge the starter battery and the alternator the tesla batteries. I used a victron smart relay between the 2.
