Guidance on System Voltage and Current Flows Truck Camper with LifePo4, Solar, Alternator, Convertor.

[rezonatefreq]

Request opinions or general guidance or pointing to article/posts for interactions of the charging source voltages, load, and batteries.

Have read many articles on the forum and elsewhere. Each seems to deal with a few of the charging sources and batteries but not as system all together with predicted current flows dependent on voltage. I realize there are many opinions on optimal charging voltages for LifePO4. That is not my main question. How do the multiple charge sources supply load, interact and charge/discharge the battery when more than one, or all are on or charging or off. My understanding is the BMS is used as battery protection relay and does not really control battery charging until limits are exceeded then it disconnects.

In my setup all charge/voltage sources are connected to the battery buss, after the BMS of course.

I do not yet have a DC to DC charger on the 6awg pair from the truck. The truck alternator voltage is not adjustable. The proposed Renolgy DC to DC is not continually adjustable. The 120vac converter voltage only has a LI or LA setting and is not continually adjustable. I still need to tweak solar charge and BMS settings but the system, as installed and programed, appears to be working ok. Charging from the truck alternator could trip the fuse or breaker when LifePO4 battery is low state of charge but it may inherently current limited by the 6awg wire impedance. Besides the BMS and solar controller meters I have Drok V/A (https://www.amazon.com/gp/product/B08JB5NQ4B/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1) meters on the cables to the battery and from the 120vac convertor.

I presume my truck could pull power from my camper when the ignition is on and the voltage of the camper battery buss is higher than the truck. This could be prevented with the proposed DC to DC convertor, isolation diode (high voltage drop) or Ideal Diode (http://www.re-voltage.eu/electronicsID80.html)

When we setup DC voltage parameters for battery backups for telecom earth stations and for the control power for prime stand alone diesel power plants we always stagger the charger source voltages in order of preferred use priority with batteries being the lowest or last use. The charge sources power all loads and charge the batteries, if needed, until the charge sources go offline or fail. We even use the engine crank batteries to keep control systems online as a last resort since without the control system voltage we can not black start the prime plant.

I have a newly installed system in my truck camper
- 8ea EVE LF280K LifePO4, 508Ah 12v, 2ea 4S in parallel, each paralleled set with its own a Jiabaida 200A 4S BMS. 6ea 12w heaters.
- Tracer AN 3210 w/340w solar, 4 panels, 2-100w,2-70w all in series.
- Progressive Dynamics PD4045, 45 amp 120vac to 12v convertor w/LI setting
- Pair of 6awg via Anderson connector from truck, only on when truck key is on, 40 amp fuse and 30 amp breaker. Presume I need a DC to DC, thinking of the Renogy 12V 40A.
- 4000w 12v Giandel Black inverter
- GoPower TS-30 120v/30a transfer switch

I have other post in the forum with photos of the system.

This is why people use the Victron MultiPlus (https://www.amazon.com/Victron-12-2...e&sprefix=victron+multi,automotive,171&sr=1-4) But what fun would that be.

 

[sunshine_eggo]

This might answer most of your questions:

Charging from multiple sources

One can have as many independent charging sources running concurrently as they like provided they are programmed properly for the voltage of one's battery bank. Examples (some or all at once, even multiples of a single type, different brands, etc.): Solar PV via MPPT Solar PV via PWM AC-DC...

diysolarforum.com

 

[rezonatefreq]

This might answer most of your questions:

Charging from multiple sources

One can have as many independent charging sources running concurrently as they like provided they are programmed properly for the voltage of one's battery bank. Examples (some or all at once, even multiples of a single type, different brands, etc.): Solar PV via MPPT Solar PV via PWM AC-DC...

diysolarforum.com

Thanks. This reinforces what I thought. I am looking for more technical detail on voltages deltas, experiences and voltage source priorities.

One good tip I did not think of was a easy and quick way to switch on/off a voltage source, like the truck alternator if needed.

I may consider adding lighted switches to my control panel. From my power generation experience we always have redundant non-software driven meters, indicator lights and switching. Software is very configurable and feature rich, but with untrained technical operators, the need for high uptime, and the increased risk of failure with high technology it always a good idea to have readily accessible manual switching and indicators.

 

[HRTKD]

Within the Victron landscape, you can limit charging to parameters over a set of devices.

 

[sunshine_eggo]

Thanks. This reinforces what I thought. I am looking for more technical detail on voltages deltas, experiences and voltage source priorities.

Voltage deltas always work the same way: Current flows from high to low. Chargers have diodes to prevent back flow from higher voltage sources, so lower voltage chargers just sit there doing nothing until system voltage drops below their output voltage.

Highest voltage has priority. Always.

Within the Victron landscape, you can limit charging to parameters over a set of GX connected and compatible devices.

Slight revision.

 

[rezonatefreq]

After letting this unpack for a spell I believe I need to measure and record the charge and absorption voltages absorption of the multiple power sources I can not adjust. For now that is the power convertor and the truck alternator. I can then make a more knowledgeable decision on which voltage source to use and how long to allow it to stay connected and if I need a DC to DC for the truck alternator.

The 45a 120 to12v power convertor seems to be the highest voltage source. From the convertor manual:
The optional OUTPUT MODE SWITCH sets the converter output to either a constant 14.6VDC with the Charge Wizard® disabled (switch in ‘LI’ position) or a nominal 13.6VDC with full Charge Wizard® function (switch in ‘LA’ position). ‘LI’ mode is intended for use with lithium batteries with a BMS requiring a constant converter output. ‘LA’ mode is intended for use with lead/acid batteries where the Charge Wizard® will optimize battery charging. I will measure this to confirm.

The convertors constant 14.6v (14.6/4=3.65) being the top limit of my EVE cells. EVE recommends 10% to 90% for "Recommended scope of SOC." 90% of 3.65v is 3.285v or 13.14v. 13.14v seems kinda low and a constant 14.6 is to high for an extended time.

I think the truck alternator voltage will vary depending on the truck battery charge state. I will try and measure voltage at the camper with the truck running and with the crank battery in various states.

This post is a good source from this forum:
https://diysolarforum.com/threads/b...mum-battery-stress-5-000-10-000-cycles.34813/

 

[sunshine_eggo]

The 45a 120 to12v power convertor seems to be the highest voltage source. From the convertor manual:
The optional OUTPUT MODE SWITCH sets the converter output to either a constant 14.6VDC with the Charge Wizard® disabled (switch in ‘LI’ position) or a nominal 13.6VDC with full Charge Wizard® function (switch in ‘LA’ position). ‘LI’ mode is intended for use with lithium batteries with a BMS requiring a constant converter output. ‘LA’ mode is intended for use with lead/acid batteries where the Charge Wizard® will optimize battery charging. I will measure this to confirm.

The convertors constant 14.6v (14.6/4=3.65) being the top limit of my EVE cells.

The reality is that the converter will "see" 14.6V LONG before the batteries actually get there. Most converter to battery connections have significant voltage drop. This is a major complaint why standard converters make poor chargers when running on generator. They take much longer to charge because the 14.6V is only held for a short period. The battery likely never sees more than 13.8-14.0V due to the voltage drop.

EVE recommends 10% to 90% for "Recommended scope of SOC." 90% of 3.65v is 3.285v or 13.14v. 13.14v seems kinda low and a constant 14.6 is to high for an extended time.

That is completely incorrect. SoC and voltage aren't even remotely linear. By your logic, you can run cells down to 0V before you use them up. Not the case. Never discharge below 2.5V/cell.

13.14V is somewhere between 40 and 70% SoC, but that's only a resting voltage, i.e., no charging or discharging has occurred for about 30 minutes. Otherwise, voltage to SoC is completely unreliable when charging or discharging.

You can't target 90% based on voltage. Period.