Comparing system prices with various battery types

[blars]

On my blog, I just posted a comparison of system prices for LiFePO4 vs AGM vs FLA for a hypothetical fulltime boondocker van dweller.  The results surprised me.  If I had wanted to bias it for LiFePO4 I would have sized the system to add 10 minutes of microwave use a day as well.  http://techno-viking.com/posts/battery-price/


I also updated my LiFePO4 resources page:  http://techno-viking.com/posts/lifepo4-resources/

 

[DannyB1954]

I looked up the LiFePO4 battery spec and it says Charge voltage cut-off: 3.6V. So for 4 batteries in series that would be 14.4 The AC charger puts out 15 volts.

My question is, Will the batteries stop charging on their own? I hear over charging kills these batteries.

The charge voltage coming from a vehicle alternator is 13.8 volts. If a separator relay is used between the vehicle and house battery, would a current limiter need to be inline to keep the vehicle alternator from supplying too much charging amperage? The spec sheet says the maximum charging current is 1C whatever that is. http://www.evsource.com/datasheets/BatteryData/CA Series Catalog - Available (1).pdf

 

[29chico]

I looked up the LiFePO4 battery spec and it says Charge voltage cut-off: 3.6V. So for 4 batteries in series that would be 14.4 The AC charger puts out 15 volts.

My question is, Will the batteries stop charging on their own? I hear over charging kills these batteries.

The charge voltage coming from a vehicle alternator is 13.8 volts. If a separator relay is used between the vehicle and house battery, would a current limiter need to be inline to keep the vehicle alternator from supplying too much charging amperage? The spec sheet says the maximum charging current is 1C whatever that is. http://www.evsource.com/datasheets/BatteryData/CA Series Catalog - Available (1).pdf

IIRC Blars likes to chage his Lifepo4 house battery bank no higher than 14v.  I am even more conservative than that and perfer to end the charge at 13.8-13.9v.  I have a low voltage disconnect (LVD) that will disconnect my Lifepo4 battery setup after one minute at 12.7v.  By not charging to as high a voltage and not discharging as low, as is commonly recomended, the battery bank will stay in much better balance and live a much longer and happier life.

You must at the minimum use a spring wound timer to disconnect the charge current.  A fully adjustable LVD

 

[DannyB1954]

I was going by what he recommended on his blog page. http://techno-viking.com/posts/battery-price/ Meanwell RSP-500-15 The output of that is 15 volts.

My main concern with a LiFePO4 battery is the maximum charging amperage. I would at times be running a generator and do not want to run it for half a day if an hour or two will do. With 2 lead acids I can run a 60 amp charger.

If I let the vehicle alternator charge the house battery, it is possible for a lot of current to go to the LiFePO4 battery as well.

 

[tbair]

I was going by what he recommended on his blog page. http://techno-viking.com/posts/battery-price/  Meanwell RSP-500-15 The output of that is 15 volts.

My main concern with a LiFePO4 battery is the maximum charging amperage. I would at times be running a generator and do not want to run it for half a day if an hour or two will do. With 2 lead acids I can run a 60 amp charger.

If I let the vehicle alternator charge the house battery, it is possible for a lot of current to go to the LiFePO4 battery as well.

I think you would not if charging at 1C and 100ah of capacity can't you charge at up to 100A? Not sure asking.

 

[SternWake]

I was going by what he recommended on his blog page. http://techno-viking.com/posts/battery-price/  Meanwell RSP-500-15 The output of that is 15 volts.

My main concern with a LiFePO4 battery is the maximum charging amperage. I would at times be running a generator and do not want to run it for half a day if an hour or two will do. With 2 lead acids I can run a 60 amp charger.

If I let the vehicle alternator charge the house battery, it is possible for a lot of current to go to the LiFePO4 battery as well.

The voltage range on a meanwell rsp-500-15 is 13.12 to 19.23 volts. User selectable.

Lifepo4 can accept huge recharge currents safely, as long as the voltage is limited.

Alternators are controlled by the vehicles voltage regulator, the voltage regulator controls the field current and makes the alternator output enough current to reach and maintain the voltage the regulator seeks

Saying they put out 13.8 volts is like saying the  entire earth is 64 degrees, always, no exceptions.

If you think a starting battery can accept a significantly higher charge current than a Marine battery of the same size, and recharge significantly faster, you are significantly misinformed.

 

[blars]

Like I said, choosing charging parameters for LiFePO4 deserves another article, which I may write. Fortunately for most users, this is set at install (based on expert advice) and should not need to be changed. 14.6v would be the maximum at 1C, or 100 amps for the 100Ah cells. (Some EV chargers do this or more. Temperature monitoring and pressure plates become requirements.) 14.0v is a bit aggressive for the 33 amps of the Meanwell, and possibly too aggressive for the 15 amps maximum of the solar. You can reach full charge at 13.8v, but it will take longer. The Meanwell can be adjusted from something like 13.5v to 15.5v with a screwdriver and voltmeter, as must be done at install for this system. Some kind of 120v timer would be an excellent idea.

 

[blars]

I have a low voltage disconnect (LVD) that will disconnect my Lifepo4 battery setup after one minute at 12.7v.

What LVD do you have and/or recommend?

 

[DannyB1954]

Saying they put out 13.8 volts is like saying the  entire earth is 64 degrees, always, no exceptions.

If you think a starting battery can accept a significantly higher charge current than a Marine battery of the same size, and recharge significantly faster, you are significantly misinformed.

OK the acceptable range of a vehicle is 13.8 to 14.6. Most of the one's I ever checked were closer to 13.8 than 14.6. There may be a voltage drop from the alternator to the house battery as well. Nothing is perfect. My concern was if I have the vehicle alternator charge a Lifepo4 battery can it feed too much amperage.  

I was taught that the thinner the plates in a FLA battery the faster it can discharge or charge, (more surface area in contact with the acid). You say it takes 3 hours to charge a deep cycle battery, I don't think it takes that long for a starter battery. The 30ah 12v LiFepo4 batteries I have looked at say a max charge rate of 10 amps. That won't work for me. I will have no solar. Whatever battery I am using I want to charge it via generator / charger at 40 to 60 amps. I still don't know what a maximum charge rate of 1C is. Never heard of it. If the max charge rate for a 100 amp hour LiFePo4 is is 100 amps, just say so.

 

[29chico]

What LVD do you have and/or recommend?

The LVD that I have is the below linked Powerwerks item:

https://powerwerx.com/automatic-dc-timer-power-switch

Only 25A continuous, but I suppose that I could run more of them with each one feeding it's own small fuse block. 

The shutoff when the voltage drops below 12.7v for two min. (longer time to disconnect possible) seems about right for the lifepo4 12v packs.

I have spoken with the Pwerks folks about how these are being used with Li packs.  I asked them to consider a higher amp output and adjustable LD voltage version.

 

[Oberneldon]

While I was designing my Prius house battery over to LiFePo4 I had correspondence with Raymond at Batteryspace.com about charge rates and this is the response I got.

6. The web page has a charge rate of 12.5A. Can you explain/relate this to the spec of Standard: 0.2C20A Max 0.5C20A? That is the terms in how manufacturer have the value figure out, 0.2C from a 25Ah battery is 5A and 0.5C from 25Ah is 12.5A.

I eventually decided to buy my 30 Amp hour LiFePo4 battery from Bioenno and opted for battery management (battery balancing) and protection circuit (over voltage/current, auto shutoff at low voltage, etc). I did add solar charging but only 60 watts due to available space in the Prius.

Brent

 

[DannyB1954]

So the "c" is a percentage of the amp hours. Then .5c would be half of what the amp hours are, as in 50%. A 100 amp hour battery rated at .5C could be charged at 50 amps. Then the 100 amp hour LiFePo4 rated at 1c can take 100 amps of charge. Seems high to me. As in maybe too good to be true. You could take 80 amp hours out of the battery and then charge it back up in less than an hour. That would be worth the premium price to me.

 

[Oberneldon]

Danny, I would recommend that you contact the company that you may be looking at and ask these same questions. I chose a company to buy from comparing products and answers to my questions so I got exactly what I wanted.

In my purchase the specs stated charging at 4 amps. In my conversations I learned that they had just updated the protection circuit inside to allow 10 amps. They warrantee their products to some extent too.

Upon receiving my battery I immediately charged it (shipped less than full charge). I then fully depleted it over days running my compressor fridge to verify internal LVD. Then fully charged it at 10 amps and as expected 30 ah battery charged in less than 3 hours.

Getting an internal BMS means you should not charge under load as when charging is done the battery goes through a 20 cell balancing cycle. I have worked around this for my purposes.

I also charge with dedicated LiFePo4 charger and charge at the 14.8 v as this is what the battery specs call for.

Brent

 

[ccbreder]

Thank you for that research. I do think it unfair to compare the price of a incomplete battery, (LiFePo), to any compleat battery, (lead acid chemisty). The LiFePo needs much more than the bare cells. Although I am surprised at the low prices on LiFePo compared to my past searches.

 

[blars]

So the "c" is a percentage of the amp hours. Then .5c would be half of what the amp hours are, as in 50%. A 100 amp hour battery rated at .5C could be charged at 50 amps. Then the 100 amp hour LiFePo4 rated at 1c can take 100 amps of charge. Seems high to me. As in maybe too good to be true. You could take 80 amp hours out of the battery and then charge it back up in less than an hour. That would be worth the premium price to me.

Yes. Many LiFePO4 are rated at 3C charge, and some allow 10C loads for short times. Due to internal heating, you'll need to cool your battery if it is abused like this, and don't expect the rated life.

Auto alternators are rated at short term rates at full RPM. A "400 amp" alternator may overheat with a 50 amp load for an hour. (and burn up if it does not have over temp protection.) To quickly charge a LiFePO4 from an alternator requires a dedicated alternator rated for continuous load with voltage regulator with remote sense programed for it, and large cables. Low charge rate tends to be the problem when using an existing alternator shared with a starting battery.

 

[blars]

Thank you for that research. I do think it unfair to compare the price of a incomplete battery, (LiFePo), to any compleat battery, (lead acid chemisty). The LiFePo needs much more than the bare cells. Although I am surprised at the low prices on LiFePo compared to my past searches.

Are you saying the "bare cells" I have been using for the past three years won't work? Why not? Lead-Acid are not more complete.

LiFePO4 prices have been pretty steady for the past few years. Lead-Acid seems to have gone up some.

 

[blars]

Only 25A continuous, but I suppose that I could run more of them with each one feeding it's own small fuse block. 

OK for the hypothetical user than won't exceed the 8A of the AGM, but useless for running a microwave off an inverter. 100mA is 2.4 Ah/day to power this small one.

 

[ccbreder]

You don't have to connect the cells together? Bracket the cells so they don't swell? LiFePo needs a battery management circuit to prevent over discharge or over charge, unless one is an expert and willing to do that manually.

 

[Oberneldon]

blars, I your comparison do you have any Li battery protection in your circuit or do you manually monitor during usage to prevent problems? Also do you balance your cells from time to time?

Brent

 

[29chico]

OK for the hypothetical user than won't exceed the 8A of the AGM, but useless for running a microwave off an inverter.  100mA is 2.4 Ah/day to power this small one.

I don't understand what you mean by "won't exceed the 8A of the AGM"

Standby on the linked Powerwerks LVD is 4mA.