DIY Composite Flatbed Camper Build

[Terra Ops]

Here is what I have for REDARC. Thoughts??
Still waiting to hear from Stark as to whether the BMS will limit the extra voltage.

 

[DiploStrat]

Look Here

In the end, the safe use of LiFePO4 depends on the battery management system. (BMS)

The tasks include:

-- Cell balancing. Huge issue for those who want to mix and match their own cells.
-- High volt shutoff. That is, too much voltage from the charger.
-- Low volt shutoff. That is, too much load, too long.
-- Low temperature protection. That is, no charge when the battery is below freezing.

If this is REALLY built into the BMS, then you are close to plug 'n pray. If not, or if of dubious quality, then you will have to add.

If you look at 2.7.2, REDARC's proposed typical LiFePO4 installation, you will note that they add a brute force low voltage shutoff relay. You can certainly do the same thing on the charge side, for high voltage.
https://cdn.accentuate.io/12384232715/41536345035/BCDC Dual Input Instruction Manual.pdf

To the proposed question, the REDARC profile is a bit higher in voltage than I would have expected, but it proposes to protect the battery by cutting the amperage. This will work, if it works.

I would speculate that REDARC, like everybody else, is mere modifying the settings on their three stage charger to fit the needs of a LiFePO4 battery, which really only needs a two stage charger - on and off. But if they drop the absorb and float amperages low enough, they can achieve the same effect. Trick is to get your battery manufacturer to sign off, in blood, that they find this profile acceptable.

The advantage with Stark is that you are dealing with the gentleman who holds some of the BMS patents used by others in the industry.

 

[rruff]

-- Cell balancing. Huge issue for those who want to mix and match their own cells.

From what I've been able to gather, if you balance your cells initially, And you avoid overcharging and over discharging, they will stay balanced a very long time. Balancing can be performed manually if needed... like once a year. An imbalance usually means that a cell has become weaker than the others, and regardless of what you do, the weak cell is going to control your capacity. The BMS simply dumps more current into the stronger cells until they are also full, but you won't be able to use that energy.

 

[Terra Ops]

In the end, the safe use of LiFePO4 depends on the battery management system. (BMS)

The tasks include:

-- Cell balancing. Huge issue for those who want to mix and match their own cells.
-- High volt shutoff. That is, too much voltage from the charger.
-- Low volt shutoff. That is, too much load, too long.
-- Low temperature protection. That is, no charge when the battery is below freezing.

If this is REALLY built into the BMS, then you are close to plug 'n pray. If not, or if of dubious quality, then you will have to add.

If you look at 2.7.2, REDARC's proposed typical LiFePO4 installation, you will note that they add a brute force low voltage shutoff relay. You can certainly do the same thing on the charge side, for high voltage.
https://cdn.accentuate.io/12384232715/41536345035/BCDC Dual Input Instruction Manual.pdf

To the proposed question, the REDARC profile is a bit higher in voltage than I would have expected, but it proposes to protect the battery by cutting the amperage. This will work, if it works.

I would speculate that REDARC, like everybody else, is mere modifying the settings on their three stage charger to fit the needs of a LiFePO4 battery, which really only needs a two stage charger - on and off. But if they drop the absorb and float amperages low enough, they can achieve the same effect. Trick is to get your battery manufacturer to sign off, in blood, that they find this profile acceptable.

The advantage with Stark is that you are dealing with the gentleman who holds some of the BMS patents used by others in the industry.

Here is 2.7.2



The installation manual does not seem to instruct as to what type of low voltage disconnect to use or as to what voltage to disconnect at. Is this not part of the BMS??

 

[CoyoteThistle]

I'll second DiploStrat - hard to know exactly what the Redarc is really doing based on the language in the manual. What they do say in the Li charging section on the first page you posted shows that they don't really understand the basics of LiFePo4 charging though. You don't need to keep the battery at 14.5v to keep the battery at full capacity. The voltage can get that high to get to full capacity, but then the battery voltage will drop to around 13.4v and it is still at (or very close to) 100% capacity. If the charger is trying to keep it at 14.5v, it is damaging the battery (unless as pointed out, the Stark's BMS is able to stop the charging). Redarc says they do it this way to counteract self discharge - lithium batteries self discharge rate is almost zero so this is nonsense.

Sterling Power has DC-DC chargers that you can set up properly for Lithium. Victron probably does too. These two companies "get" lithium charging in vehicles.

Either way, I would add the cheap insurance of a quality low voltage cutoff no matter what Stark tells you they have built in. Mine is a Victron BP100 and was about $60. Over charging will decrease your battery capacity over the long run, but if you accidentally over discharge them, they might be a complete loss. Very easy to wire in. Should be set no lower than 11.0v. I have mine at 12.0v just to be safe.

 

[Terra Ops]

Thanks for all the great input! Hope I didn't just blow some $$$$.
Sounds like it will come down to the BMS in Stark's Lithium.......Stay tuned

 

[DiploStrat]

The low voltage disconnect voltage, as well as the high voltage, will depend on the battery.

You would use something like this: https://www.aliexpress.com/item/Voltage-detection-module-car-battery-under-voltage-protector-measuring-charging-and-discharging-monitoring-shell-5-12/32829526754.html?spm=2114.10010108.1000013.5.3302bd76Q6lrY3&traffic_analysisId=recommend_2088_3_90158_iswistore&scm=1007.13339.90158.0&pvid=f9924e20-859a-46bf-8090-3b6d93d5c8ad&tpp=1

Put it in the control side of a relay of the appropriate size.

You could also use this, but it is much more expensive: http://www.magnum-dimensions.com/smart-battery-combiner

REDARC is a well established company with a very good track record. Using two of their chargers, I can confirm that they work as advertised with Lead Acid. Lithium is a whole new world but I suspect that what they are doing will work. Within limits, voltage and amperage are reciprocals - so keeping the voltage high while killing the amps has the same effect as dropping the voltage. Just depends if they have done it properly. Also depends on what is sold in the Australian market.

Worth noting that feeding a lithium battery 14.Xv is not a problem as long as you stop, or cut the amps, when the battery, not the charger, hits just over 14v. These are the voltages for most commercial available "plug and play" "12v" LiFePO4 batteries.

FWIW, REDARC products have a good reputation for reliability, unlike Sterling, which has just the opposite. Doesn't mean that I would rule out Sterling, but I would make sure that I had good return guarantees.

 

[rruff]

View attachment 430435

I guess you are cutting a hole in the back of your truck for this? Looks like it would need to be since it is low.

I was thinking of making an open that would match up with the truck's window. The window would be replaced with a piece of plastic with a hole matching the camper opening. But I may change my mind about that...

 

[Terra Ops]

I guess you are cutting a hole in the back of your truck for this? Looks like it would need to be since it is low.

I was thinking of making an open that would match up with the truck's window. The window would be replaced with a piece of plastic with a hole matching the camper opening. But I may change my mind about that...

Already have the cut out. Had it custom made with my pop up. Shouldn't be too difficult to do, you may be able to fit an existing frame/door from something like a tear drop camper.

 

[Terra Ops]

Info on the Stark battery; listed on their website
Looks like max charge of 14.6 is fine? Discharge too?

https://starkpower.com/product/12-volt-125ah-battery


Voltage 12V
Capacity 125Ah, 1600Wh
Chemistry LiFePo
Weight 34.2 lbs (15.5 kg)
Dimmensions 319 x 165 x 234 mm
12.55" x 6.5" x 9.2"
Life Cycles 3,000 @ 80% DOD
BMS Yes (Internal)
Max Charge Voltage 14.6±0.1V
Discharge Cut-Off Voltage ~10.0V
Max Charge Current 80A
Max Discharge Current 100A
Peak Current (3s) 350A
Operating Temperature -20~60℃ -4℉~140℉
BCI Group Size 31
Terminals 5/16 UNC Thread

 

[rruff]

I'd feel more comfortable with 14.4v and 12.0v, but I assume they know what they are doing. Looks like the BMS also has a low temperature cut off.

Have you asked them about alternator charging? I hear most modern alternators stop in the high 13s, and this isn't near enough voltage for a full charge.

 

[Terra Ops]

This is what Stark's Chief Technical Officer "CTO"? had to say;

StarkPower's battery management system (BMS) is inside each battery case and uses high power MOSFETs to turn OFF or ON the power from the terminals instead of using solenoids to allow for a compact, faster turn-off with higher reliability. Using StarkPower's patent awarded MOSFET configuration also allows for enhance controls to turn OFF or ON the battery terminals. An example using this features is detecting a charge voltage when the battery terminals are OFF to turn the power terminals ON .

You can use the Redarc DC/DC charger controller to charge up to 14.6V, in the pdf file charges to 14.5V which is fine as well. If a single voltage goes to 3.8V/cell then the BMS will turn off the terminal pathway as a secondary protection. The float voltage on the Redarc is very good. I don't see any issues with using the DCDC charger with StarkPower's LiFePo4 batteries

Very impressed to get a response from the CTO and get confirmation that my set up will work

 

[Terra Ops]

"I hear most modern alternators stop in the high 13s, and this isn't near enough voltage for a full charge"

It is my understanding that the REDARC unit not only protects the vehicles electronics but also compensates by boosting.

 

[CoyoteThistle]

This is what Stark's Chief Technical Officer "CTO"? had to say;

StarkPower's battery management system (BMS) is inside each battery case and uses high power MOSFETs to turn OFF or ON the power from the terminals instead of using solenoids to allow for a compact, faster turn-off with higher reliability. Using StarkPower's patent awarded MOSFET configuration also allows for enhance controls to turn OFF or ON the battery terminals. An example using this features is detecting a charge voltage when the battery terminals are OFF to turn the power terminals ON .

You can use the Redarc DC/DC charger controller to charge up to 14.6V, in the pdf file charges to 14.5V which is fine as well. If a single voltage goes to 3.8V/cell then the BMS will turn off the terminal pathway as a secondary protection. The float voltage on the Redarc is very good. I don't see any issues with using the DCDC charger with StarkPower's LiFePo4 batteries

Very impressed to get a response from the CTO and get confirmation that my set up will work

The response from Stark is entirely consistent with their position that they are selling a "drop in" lithium battery and since the DC-DC converter is doing more or less what an alternator does (only better), it makes sense that they see it as compatible.

What is missing from this response is a statement saying that their BMS disconnects the battery from charging at somewhere between 14.0 and 14.6 volts and re-connects charging at ~13.3 volts (below the resting voltage of a fully charged battery). Unless you are stopping charging once the battery is full, you are slowly damaging it. "Float" charging should never be done with lithium (disturbing to see the CTO endorse it). Keeping it at 14.5v whenever you are charging is damaging the battery. Their 15.2v cutoff (3.8v per cell) is appropriate for protecting the battery from immediate damage (if for instance a voltage regulator somewhere in your system fails).

All that being said, you've got good batteries there. I would just spend the extra couple hundred bucks adding in a proper control to turn the charging on and off unless you can get Stark to say their BMS is doing that at the approximate voltages referenced above.

Sorry, feel kinda like your thread is getting hi-jacked here on a tangent - I'll go back to silently enjoying this cool build

 

[stomperxj]

I hear most modern alternators stop in the high 13s, and this isn't near enough voltage for a full charge.

Not really true. My standard GM Delco alternator consistently puts out 14.5+. Most newer vehicles have some sort of battery control module so they have lower output when the extra isn't needed. I know the GM BCM will cut the alternator down to 13.0 +- when cruising.