Sloya,
I understand that you think you have a workable system despite defying conventional wisdom. So rather than simply throwing darts, I tried take the information you provided and determine what can be deduced from that data. In certain instances, I introduced other typical/standard information related to charging LiFePo4 cells.
You have done a good job of researching your system and the tradeoffs, but there are some of your conclusions that need a little more detailed analysis. The primary one of course, the evidence will tilt toward a DC-DC Charger to match your battery system even though you may not need it for your particular (low) consumption profiles.
Quote:
Originally Posted by Sloya
Mine has a steady 14.0 volts
output. The thing that saved me from having to add a DC to DC charger was the fact the Blue Sea Battery Isolator charges the batteries to 80-90 percent charge, not 100 percent. Because of this fact it prevents the high charging that is known to burn up alternators using lithium batteries.
|
What burns alternators is too high of a current demand that exceeds the cooling capacity of the alternator. Cooling capacity in minimal at idle because the built-in fan speed and airflow are minimum. Lithium batteries have low internal resistance which means they more readily accept charge and are capable of demanding large currents from an alternator. Generally, this is not a problem except when a DC-to-DC convertor is installed. The DC-DC has a built-in boost battery charger that operates down to > 9volts typically. The DC-DC tries to maintain the (selected) rated current e.g. (40Amps @ 14V) but to do this with 10 V at the input terminals (voltage drops between DC-DC and alternator, or overtaxed alternator outputting less than 14V) it would have to boost the voltage making the alternator current draw much higher (e.g. 40*(14v/10v)*(100%/.90%)) = 40*1.54=62 amps! This is what can overheat the alternators. Some type of control must be used. A simple control is only activating the DC-toDC when at highway speeds. Alternator thermal control is another)
Quote:
Originally Posted by Sloya
Here is the trade off using the Blue Sea, you only get a max of 90% charge while driving. If you are one of those who has to have 100% charged batteries, you can spend the extra money for that last 10% of charge. Having solar takes care of charging the batteries to 100% during the day, and if you have shore power you are all set.
|
I tried to track down what your logic was for this statement and found this.
Quote:
Originally Posted by Sloya
Let's start, you are absolutely correct about the Blue Sea ACR not knowing anything about Lithium. However it does know to switch off at around 13.7v. I think if you do the math it would equal that 80-90 percent charge status you see in the SMB manuals for house battery charging. I have come across a couple of manufactures that make something similar but has an adjustable voltage setting allowing you to increase or decrease the switching point. I find the Blue Sea doing what it does best and no need for the 100% charging during driving. When I arrive at a site 80-90 percent is plenty to get me through the night. The next day the solar will pickup or I will be driving again. From everything I have read lately is that by not charging to 100% you increase the battery life of lithium batteries. This is a big plus considering the cost of lithium batteries.
|
I would be very surprised if the Blue Sea ACR stops charging when the Lithium is at SOC=90% even if it does switch off at 13.75V. I don't think you have considered the significant voltage drops you could be getting between the Alternator and you LiFEPO4 battery and another unknown is where in that ACR is in between (it affects how much of the alternator-battery voltage drop it sees)?
If your alternator is only outputting 14V at the alternator terminals, then you only have about 0.5 Volts before your Lithium terminal voltage is only 13.5V. I ran some numbers for your 315 amp-hr battery array. If you had 2,5,8 AWG wire you would push 31.5A,15.8A,8A respectively ( through the wires between the alternator and battery array ) without dropping below 13.5V.
It is a little difficult to estimate how much current the alternator is pushing to your 315 Amp-hr LiFEPO4 bank; the easiest thing is to see how much it outputs with a current clamp at the input of the battery bank.
https://www.amazon.com/UNI-T-Digital...xEALw_wcB&th=1
As Porschedpm had suggested you can install a battery Monitor and get a good idea of capacity as well as voltage and amps into the battery bank.
It is difficult to get the State of Charge of a battery without understanding how charging and discharging is affecting (i.e. through internal resistance) your battery terminal voltage measurements. If you are monitoring battery voltage from the alternator all bets are off.
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
Your Solar Charge Controller, a 120V to 12V DC battery charger and a DC-Dc convertor all have one thing in common. They all have a lithium battery charging interface. They only differ in where the power is coming from (solar, vs shore power vs alternator).
In the Renogy 40Amp DC-DC manual they have absorption voltage levels programmable for a Type 1 (13,12.8 and12.6v ) and Type 2 (14.6, 14.4, 14.2. and 14v). The LiFEPO4 is the Type 2 category. To properly charge LiFEPo4 you generally need more than the 14.0V you say your alternator is supplying (even if that is at the battery terminals)?
Quote:
Originally Posted by Sloya
Right now we are in the winter season and the solar is keeping up with charging duties while the SMB is parked. On a good day in full sun the solar charges approximately 50 Ahrs and on a short day about 21 Ahrs.
|
At full sun your 200W system, is only delivering 10amps? It seems the Zamp charger is PWM. I regularly get close to 30 amps out of a 435 watt used panel with a MPPT charge controller. That is probably about 50% better conversion efficiency.
These are a good deal by top-name company that should noticeably increase you solar production.
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
Quote:
Originally Posted by Sloya
In Summary, I was able to make the switch to Lithium without any additional major expenses except for the batteries themselves. Having equipment that was compatible eliminated any hardware changes that would have pushed the price higher. During solar charging the battery voltage goes as high as 14.4v but averages 13.3v and goes as low as 12.9v during high use. When using the coffee maker with 85 amps being used the voltage goes to 12.4 as the lowest and as soon as it stops it shoots right back to 13.0v. I find the controller electronics works better with the built-ins appliances in use. I know this report makes it all sound simple but believe me when I say I moved very
cautiously, reading everything I could find on the subject before making the battery purchase. Once this was done it was game on!
I hope you find this informative thought provoking, it works for me.
|
Your Solar charger despite being PWM knows to charge at 14.4v well above what is available from your alternator. If it drops to 13.3v it is because of pretty heavy loads exceeding you solar charge currents. With an MPPT mentioned above these voltages should rise closer to the 14.4 level.
At 13.0V, SOC~20-30% and apparently enough to handle an 85 amp draw but it is the very low side. The LiFEPO4 SOC chart starts to drop precipitously at 12.8V and by the time you are at 12V SOC~10% . It is not good to be running at these low levels.
Generally, I think that you have improved your situation with Lithium probably more usable Amp-hr capacity (than your older AGM batteries, and faster charging LiFePO4 for the properly configured solar charger.
That said, depending on your system voltages, the MPPT is superior to the PWM MPPT solar charge controller. Finally, the alternator charging is unverified as such (no charging current measurements) but based on other circumstantial evidence it is likely not very effective without DC-DC charger.
Finally, your 21-50 Amp-hr daily solar replenishment can be used to approximate your daily consumption requirements corresponding to 6.7% and 16% respectively as %SOC for a 315 amp-hr battery bank.
Nowhere have you said directly where this minimal daily pattern is riding (top, middle or bottom of the SOC?) except when you said that your battery gets occasionally down to 13.0 (about the bottom).
The bottom line is you have much more battery (315 amp-hr) than charging capacity (Solar, Alternator) or for your usage pattern (21-50 Amp-hr).
Regards,
PS: if you are wondering I am an EE in the process of designing my own solar/battery system. Just this week have been testing two sets of 300 Amp-hr AGM batteries to couple with 200 Amp-Hr DIY LiFePO4 to handle 12V Rooftop Air Conditioner loads.
AWOL
(No name yet)
CSC TT250 + homebuilt trailer
Linear Mode
