Charging a 300 ah battery with a 280 ah charger

[Wyuna]

I’ve got a Votronic triple Charger that can charge up to 280ah for Lithium (4 different charging profiles)

Ive just sold my AGM's and looking at Lithium, as prices have reduced a bit here.

But there isn't much range between 200 ah and 300ah battery over here, so I was thinking, of the 300 ah, setting the charger at 280ah and setting the DOD to 20% so that would give me 240 usable amps.

The Votronic battery monitor keeps a eye on how many amps have been used and works of that for SOC

Technically, I’m not charging over 280 ah


Any major issues with my plan…

 

[john61ct]

No such thing as a charger rated in AH.

That would be Amps, and 60-120A is appropriate for that size bank, depending on chemistry.

What model batts?

 

[john61ct]

Oh I see some vendors give guidelines on sizing.

That can be mostly ignored, go by Amps current output.

Minimums vs maximum by batt type

FLA .15-.20C , lower is just slower
AGM .20-.50C, lower hurts longevity
LFP low is fine is LOTS slower, up to .8C but can get hot

 

[john61ct]

State your desired AH capacity, charger amps, and link to proposed LFP battery.

 

[Wyuna]

The german triple charger i have puts out 30 amps DC-DC, 20 amps via 230 volt AC charging and up to 250 watts of solar (i've got 180 watts on the roof)

The lithium charging profile id look at is 14.2 volt then steps down to 13.6volt.

At this stage, id just be grabbing a pre made set of GBS 300amp Cells with a Relay BMS too make up a 12 volt system.

https://www.ev-power.com.au/product/ev-powerpak/

in hindsight i should have gone the next model charger, but at the time this suited me fine and its what i have.

from what i understand, is that lithium doesn't like to be full 100% of the time, unlike AGM.

 

[rayra]

Lithium batts don't like deep discharges either. And they don't last as long, regardless of how you use them. Doesn't seem to make much sense to get rid of your AGMs to go with Lithium in a camping vehicle?

 

[john61ct]

Ignore that last, bulldust.

The german triple charger i have puts out 30 amps DC-DC, 20 amps via 230 volt AC charging and up to 250 watts of solar (i've got 180 watts on the roof)

The lithium charging profile id look at is 14.2 volt then steps down to 13.6volt.

At this stage, id just be grabbing a pre made set of GBS 300amp Cells with a Relay BMS too make up a 12 volt system.

https://www.ev-power.com.au/product/ev-powerpak/

in hindsight i should have gone the next model charger, but at the time this suited me fine and its what i have.

from what i understand, is that lithium doesn't like to be full 100% of the time, unlike AGM.

For longevity, create a lower definition of Full, I use 13.8V and stop, no Absorb no Float.

But some chargers are not fully adjustable.

Only charge to Full when active loads will start pulling down.

Keep at low SoC when not cycling.

With 300AH you could easily go to 150A or higher.

Using a slow rate will just take more time.

 

[Wyuna]

Thanks John,

I can't imagine, why anyone wouldn't consider Lithium over AGM if they already have a charging system that will do the job.

I'll save over 30 kg in weight, increase my usable ah, and the draw rate is better for the new 1200 watt inverter i'm about to install.

the only con, is that they are 3 times the price of a decent set of AGM here.

Anyhow, back to the charging settings, while its not fully adjustable, there is a 13.9V setting and i can set it to stop charging once its full.

I could look at a circuit breaker to stop the charge, while not using the camper as a camper and keep it a low SOC

 

[john61ct]

Stateside the cost diiferential is 7x, and that's ordering bare cells direct from China without BMS.

And true deep cycling FLA, more robust than AGM is $1/AH@12V so hard to justify.

And fully adjustable high-amp charger is expensive, DIY BMS a technical challenge.

We have no vendors like Mannum.

 

[luthj]

A bit off topic, and no personal experience, but I have seen a few pre-built lithium packs that could easily drive an external disconnect. This one also has temp and voltage monitoring (plus high rate balancing if needed).
http://www.manzanitamicro.com/produ...page=flypage.tpl&product_id=52&category_id=19

With lithium packs ending absorb by return amps is ideal (around 6-10% or C?) Otherwise a very short absorb timer, somewhere around 10 minutes works. There is no real advantage to sitting at a higher voltage once the 90-95% full mark it hit (for a RV application at least).

 

[john61ct]

I have seen a few pre-built lithium packs that could easily drive an external disconnect.

sorry, please clarify what you mean?

I'm inferring "has an internal BMS that can be set to isolate the bank from a charge source when full, or from loads when depleted"

Is that close?

 

[luthj]

Yes

sorry, please clarify what you mean?

I'm inferring "has an internal BMS that can be set to isolate the bank from a charge source when full, or from loads when depleted"

Is that close?

Yes, in this case the relay(s) is separate and external from the pack/bms.

 

[Wyuna]

Well i ended up finding and ordering a drop in 240 ah Lithium battery, i'll still have an increase of usable Ah, over the 280 ah set i had at 20-30% DOD

Also, its a 49Kg weight reduction, so that a great bonus for my van

This also comes with a 3 year warranty, so it was better than the 12 months that were offered by the others i looked at.


Specifications B-LFP 12V240Ah
Voltage 12.8V
Nominal Capacity (25°C , 0.2C) 240Ah
Weight (Approximate) 29.0Kg
Cell Prismatic
Dimension L*W*H 520*269*203mm
Specific Energy 80Wh/kg
Standard Discharge 25°C Max. cont. current 240A
Max.10sec.pulse 240A

Standard Charge Charge Voltage 14.6V
Float 13.8V
Style CC/CV
Recommended Charge Current 120A
Using Temperature Discharge -30 to 60℃; 0.1C Charge -20 to 60℃
Storage Temperature -30~60℃

I'll look at the further spec sheets once it arrives, and i'll use the 13.9 volt setting and set up the charger disconnect feature.

Time will tell if its any good.

 

[Joe917]

Cost?

 

[Wyuna]

$2099 AUD, so $1550 USD at todays rates

A decent set of AGM here is between $800-$1000 for 280 ah AGM