Charging Li batteries

[Al F]

 

I don't understand why a BMS needs to be involved with both a charger that knows when to stop, and a battery that has built-in protection. The SmartBattery site doesn't list such a product. Is it because you think 14.4 is too high? Or because you want it to disconnect?

 

I understand the need for a monitor to know what the SOC is.

I want a BMS with a monitor so I know what my very expensive batteries are doing.

 

Kind of like idiot lights on a car years ago. The idiot lights work fine on a car I drove to an from work. On the other hand with a truck or motorhome engine pulling a load I want to know what is going on. I don't want just know that as I am pulling up a long climb that the engine or transmission is over temp and it shuts down. I want to know before it reaches the max or min so I can take steps be sure I don't reach those points.

 

By the same token I use my LFP batteries extensively, just like the truck or MH. So I want to know what they are doing, not just that it stops when it reaches the max limit.

[hemsteadc]

Something I'm not quite grasping about charging using solar:

 

The recommendations I'm getting for shore power charging is to have a separate 12v charger for each battery. Yet, the guy at SmartBattery, and the other websites I've been to talk about using solar just as with LA batteries. Now, I can't imagine each of these Li 12v batteries having its own separate solar controller. In in my case, I'd be charging @ 48vdc, which the guy at SmartBattery says is just fine.

 

This isn't making sense to me.

[hemsteadc]

I'll try bumping this to see if anyone can answer.

[Ronbo]

I have 1000 watts of solar charging 600 amps of li batteries. If I need to charge from shore power (haven't required it Since installed) I will use my inverter/charger as I have it programmed for my li bank. How are you going to wire your batteries? Are you going to have a BMS for the li bank?

 

One solar controller charges full bank. At 100% by 10 every morning.

[Al F]

Something I'm not quite grasping about charging using solar:

 

The recommendations I'm getting for shore power charging is to have a separate 12v charger for each battery. Yet, the guy at SmartBattery, and the other websites I've been to talk about using solar just as with LA batteries. Now, I can't imagine each of these Li 12v batteries having its own separate solar controller. In in my case, I'd be charging @ 48vdc, which the guy at SmartBattery says is just fine.

 

This isn't making sense to me.

Which are you asking about, Shore Power, or Solar Controllers? You have both in your posting and it isn't clear to me which you are asking about.

 

With solar, you do need to have your solar panels wired together to supply more than 48 volts to a solar controller which will supply the nominal 48 volts.

 

Do you have a solar controller which will supply 48 volts? If not you need 12V solar controllers for each 12V battery.

 

Now with the BMS to monitor the Li battery bank, my BMS is set up to monitor for 12V nominal Li voltages. I would have to study the wiring on my Li bank and BMS to see exactly how I would keep the BMS at 12V while the battery bank would be wired in series for 48V. I don't think it would be a problem.

[Ronbo]

My BMS monitors at the cell level. It doesn't matter how many volts it is wired for.

[hemsteadc]

Which are you asking about, Shore Power, or Solar Controllers?

I'm asking about why solar is "perfect" for Li batteries (in my case 4 12v in series charging at 57v) whereas the sellers of these batteries do not recommend charging at 48v on shore power. They recommend using a separate 12v charger for each battery.

[Jim Gell]

Let me add to the discussion:

 

When I had a cell monitor go bad, I bought all new ones as well as this HousePower BMS circuit board. It comes in a 48V nominal bank voltage option. It monitors cell level conditions and bank level. Unfortunately, my system is set up so that the BMS triggers a single solenoid to disconnect the battery for over or under charge conditions. This could be problematic, as Timon said, in that if it's overcharged, I can't easily drain off power, and likewise if it trips off for low voltage, I can't easily charge the battery. I have not had a single issue with it since the first cell monitor went bad last Winter, but now that I know it can happen, I bought a small cell level charger/discharger. Maybe, I should get a better BMS?

 

I have my battery bank in my 5th wheel bedroom where temperatures extremes are moderated.

 

Jim

[Al F]

My BMS monitors at the cell level. It doesn't matter how many volts it is wired for.

True, my BMS monitors at the cell level same as yours. However the BMS computer operates off of 12V, so I would need to be sure I only tapped into 12V and made sure I didn't try to power the computer with 48V. Shouldn't be a problem, just tap into one of the 12V packages.

[Al F]

I'm asking about why solar is "perfect" for Li batteries (in my case 4 12v in series charging at 57v) whereas the sellers of these batteries do not recommend charging at 48v on shore power. They recommend using a separate 12v charger for each battery.

I guess the sellers won't tell you why they only recommend shore power charging with 12V and not a single 48V charger?

 

Maybe it has to do with charging the center batteries in the 4 battery string. With the 48V charger you will attach the minus lead to the battery on one end of the string, and the plus lead to the other end of the string. The charging current to the center two batteries goes through the end batteries before getting to the center batteries.

 

I have read (I don't remember the source of the documentation) about the all the batteries in a string not getting the same amount of charge if the charging current is only applied to the end two batteries. I believe it has to do with the internal resistance of the individual batteries and the resistance of the connecting cables and connectors.

 

However you have the same problem if you charge at 48V from solar.

[Ronbo]

Jim, the specs say you can use two relays, one for high and one for low voltage. That would allow you to use power if overcharged but stop charging or stop flow if undercharged but keep charger connected.

 

Al, I believe the unequal charging is when they are connected parallel. There are ways to connect the batteries and charger so the charge is very close to equal.

[hemsteadc]

I believe the unequal charging is when they are connected parallel. .

I hope that proves to be true

[Al F]

Here is a link to the website I saw the info about unequal charge/discharge and battery wiring. Note: I'm not here to support or refute the info, just use it as you see fit.

 

I used method #3 to wire my 4 lithium batteries in parallel because this method made good sense to me and wasn't hard to accomplish.

 

Wiring four 12V batteries in series for 48V would be totally different since you would only have one load cable each going to the end plus and minus battery terminal. I don't know if there is any issue about charging the center two batteries where all the charging current has to go through the two outside batteries before getting to the center batteries.

 

In thinking further, with the 4 batteries in series, the current has to flow through 3 batteries to get to the last battery. I would think that the internal resistance of the batteries would have some affect.

 

I'm pretty much just thinking out loud about the 48V battery string. I have only dealt with 6V battery pairs in series for 12V so I have no idea if there are any issues with charging/discharging four 12V batteries in series.

 

I'll shut up now.

[VallAndMo]

Hi Al Florida,

 

Great link, thanks for sharing. I actually remembered Kirchhoff electrical network analysis which I had last seen in high school (!), and the guy is right, the actual calculations are awful.

 

But once we think about the resistances (both in the cable and in the interconnects, and also each battery's internal resistance), method #3 seems intuitively right, method #4 not so much... So, when the time comes for my install, if I have the necessary space for the extra terminals I will follow your lead and do #3 too.

 

Cheers, and thanks again,

--

Vall.

[VallAndMo]

Hello everyone,

 

Just saw this announcement for a live video chat on the subject of lithium batteries and installations, featuring both Nina&Paul (Wheeling It) and Cheri&Chris (Technomadia), and thought that perhaps it would interest people here:

 

https://livestream.com/accounts/10991713/lithium

 

Cheers,

--

Vall & Mo.

[hemsteadc]

 

Do you have a solar controller which will supply 48 volts? If not you need 12V solar controllers for each 12V battery.

Yes I do. I have the Outback 60, so yes, it does 48v. I've still not gotten a definitive answer from Smartbattery on the 48v series charging.

 

EDIT: I read on Amazon (who handles Smartbattery) that the company gets an F from the BBB due to numerous complaints of poor delivery and bad service. I looked it up and yes, it's true. I guess I'll be dealing with Nexgen.

 

EDIT2: Now the Nexgen site is unreachable.

 

Just a wild idea.. is it possible to use my Outback to charge at 12v by running 2 wires to each of 4 batteries, all ganged together on the controller's output lugs? There would be 4 wires each from the + and - terminals.