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Discussion Starter · #103 ·
Just to get everything I can think of in one place.

Updated list of electrical needs and wants.

1. refrigerator (40 watts)
2. hot water [unknown power, possibly as much as 1800 W]
3. water pump [minimal power, typically less than 100 W]
4. LED lights [likely a few tens of watts]
5. device charging [as much as a couple hundred watts if charging a laptop plus multiple mobile devices]
6. small tv [likely less than 100 W]
7. gasoline heater (14 watts)
8. air conditioner (410 watts, occasionally)
9. inductive cooking plate (main cooking using camp stove)
10. microwave?
11. roof fan


Camper van usage:

Daily driving with occasional stops of 2-3 days. Starting ICE engine 220A alternator is perfectly acceptable to charge house battery. I have a 140A smart battery isolator to charge if it would be suitable to the house battery.

Aircon will be just to cool down van couple hours before sleeping as needed. Rooftop fan for night sleeping.

Option for small 1000W/800W generator as needed.
 

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Discussion Starter · #104 ·
Concerns on using FLA or AGM:
1. Voltage sag under load falsely hitting low voltage cutoff on inverter reducing house battery usage, even with a fully charged battery. Especially apparent if running microwave or aircon. This wouldn't happen using LFP pack as lithium doesn't experience voltage sag nearly as bad.
2. FLA is messy and I'd rather not deal with it. AGM's can be mounted sideways under van. So can LFP. FLA needs to stay upright of course, and properly vented.

400Ah AGM and LFP can both be discharged 80% without greatly reducing cycles. FLA can't discharge 80% without greatly reducing cycles.

I'm open to AGM or LFP.
 

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Besides fuel consumption, what's the difference if I run a small 1000W/800W genny running an inverter/charger or the ICE engine with electronic battery isolator charging house battery?
Note all the isolator (combiner / VSR) does is stop Starter from going flat, nothing to change the charging.

Running your propulsion engine for many hours per day is silly, very expensive and harmful to its longevity.

Every hour like driving 30-40 miles, just wear and tear.

And alt output will only reach over half rating at much higher rpm than idling.
 

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1. Voltage sag under load falsely hitting low voltage cutoff on inverter reducing house battery usage, even with a fully charged battery. Especially apparent if running microwave or aircon. This wouldn't happen using LFP pack as lithium doesn't experience voltage sag nearly as bad.
Well you can wait for guesses or calculate it yourself pretty easily. Most of the AGM batteries you are interested in specify Internal Resistance. For example a Fullriver DC400-6; a 6-volt 400 AH AGM specifies Ri = .0016 Ohms. It would take 2 in series for 12 volts thus total Ri = 2 x .0016 Ohms = .0032 Ohms.

From there is simple Ohm's Law Voltage = Amps x Resistance. So at say C/4 or 100 amps x .0032 Ohms = .32 volts sag or on a 12 volt system is 2.7% loss. Add another 2 to 3% for cable and connectors and you met a reasonable 5% or less loss.

FWIW broaden your horizons. Go look at one of the 400 AH LFP cells. Just about all of them will list Ri. For 12 volts you would need 4 in series. So multiply the Ri by 4 and tell me if it is higher or lower than the 400 AH AGM. What you are going to gain from that will surprise you because it will be exact opposite of what you are expecting. It will tell you which battery has the higher Specific Power which is expressed as Watts / Kilogram. Put another way how high a C-Rate the battery is capable of. So go see what you find, and tell me what you think.

Last part of your question regarding FLA. A 6-volt 400 AH battery Ri= will be higher than AGM by about 50% or around .002 Ohms. So they will not have quite a high as a C-Rate. Here is what trips up people. Lithium Batteries C-Rate is a THERMAL LIMIT, not a Performance Specification like all other batteries are measured by. So when you see a CALB rated at say 3C continuous and 10C Burst is a Thermal Limit. At those levels voltage sag will be extreme . Now that you looked up a 400 AH Lithium, do the math at 3C. On the AGM is 1200 amps x .0032 = 3.84 volts.
 

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Voltage sag under load falsely hitting low voltage cutoff on inverter reducing house battery usage, even with a fully charged battery. Especially apparent if running microwave or aircon. This wouldn't happen using LFP pack as lithium doesn't experience voltage sag nearly as bad.
Yes. Counteracted by going bigger AH capacity.

AGM's can be mounted sideways under van. So can LFP

Nope, apparently reduces lifetime, but depends on maker. Risky at least.
 

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400Ah AGM and LFP can both be discharged 80% without greatly reducing cycles.
Nope, all three get many times greater lifetime by cycling more shallow.

LFP costs so much and go so many thousand cycles anyway, people don't do it much, although some reserve is good.

AGM is particularly harmed by deeper cycling, IRL much more so than in the lab charts. Combined with PSOC conditions can murder them in a single season easy.
 

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sportecoupe one more design tip. Be real careful with On-Line Wire Size Calculators. They will get you in trouble real quick. Most have a serious FLAW. They only calculate the Resistance required to meet a voltage drop. What they do not do is check their answer to see if it meets any listing agency thermal limits. The Flaw is it will give you too small of aa wire on short distances of 15 to 20 feet or less. Example say you have a 300- amp fuse and want 2% at 10 loop feet, and you will get an answer of 2/0 AWG copper which is too small fine for an EV because that is peak for a few seconds, but not on Power Wiring like an Inverter where loads are continuous.

My advice to you and anyone interested is use this Table. Find your Fuse or Breaker size, find the Distance. This Table is for Marine which exceeds SAE and NEC standards which means you can sleep at night. Note 300 Amps is not listed. For 300-Aamp Fuse requires a minimum 4/0 AWG Copper at 10-feet loop distance.



Note wire size is not based on Load Current. Minimum wire requirement is sized to the Fuse or Breaker size feeding the wire. A 3000 watt 12 volt Inverter requires a 300 amp circuit. Good luck with that and 4/0.



 

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Discussion Starter · #111 ·
sportecoupe one more design tip. Be real careful with On-Line Wire Size Calculators. They will get you in trouble real quick.
Thanks for the handy chart.

Wire size calculations in aircraft get even crazier. They of course need voltage, load and length but also add number of wires in bundle, altitude and air temperature of the area they are installed in during flight. :eek:

I've never had to design for more then 15 amps @28v per component though for the systems I integrate into the aircraft.
 

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Discussion Starter · #112 ·
FWIW broaden your horizons. Go look at one of the 400 AH LFP cells. Just about all of them will list Ri. For 12 volts you would need 4 in series. So multiply the Ri by 4 and tell me if it is higher or lower than the 400 AH AGM. What you are going to gain from that will surprise you because it will be exact opposite of what you are expecting. It will tell you which battery has the higher Specific Power which is expressed as Watts / Kilogram. Put another way how high a C-Rate the battery is capable of. So go see what you find, and tell me what you think.
LFP Ri is double some AGM batteries. I didn't expect that. :eek:

Fullriver's DC400-6 AGM Ri (0.0016 x2 = 0.0032) is more then double Lifeline's GPL-L16D AGM (0.00068 x2 = 0.00136). :cool:
 

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Discussion Starter · #113 ·
Yes. Counteracted by going bigger AH capacity.

AGM's can be mounted sideways under van. So can LFP

Nope, apparently reduces lifetime, but depends on maker. Risky at least.
Bigger Ah - ok more is better, two Lifeline 6V 400Ah AGM should be fine for voltage sag.

I'm assuming you mean AGM cannot be mounted under van? I don't see a reason why not. Operating temp range is -40F (-40C) to 160F (71C). I would use a steel skid plate (or box) to protect from road debris.
 

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Discussion Starter · #114 ·
current and power demands should still be non-issues for this size of battery at 12 volts.
Yes.

The "challenge" with aircon is not the current, but the kwh per day consumption.
Aircon use on batteries will be limited. Max 2 hours a day (maybe?).

Continuous use of aircon, I would connect the small genny or go for a drive to run ICE.
 

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LFP Ri is double some AGM batteries. I didn't expect that. :eek:
I tried to tell you that in PM's but you were not having any part of AGM out performing LFP. Amp Hour per Amp Hour, AGM out performs Lithium with respect to high current. I had to have you discover it for yourself. The math does not lie.

I will be real honest with you, From what you have stated in this thread, you have not justified an Inverter greater than 1000 watts, 1500 watts is over kill.

If you buy a quality Inverter/charger/ATS of say 1000 watts is continuous power, 2000 peak. So I know 1000 makes you nervous, then go with 1500/3000 which is way more than enough. You wil be able to drop conductor sizes down to 4 or 2 AWG. Remember you are using continuous currents for power and lighting. Not burst currents used in an EV. Different rules and practices for different applications.

For RV's I use Marine Standards because they exceed NEC and SAE codes. SAE and NEC do not take voltage sag into consideration. Additionally all marine cables are rated for 105 degrees C, wet/ damp, and if you buy Marine Battery Cable you get oil and gas resistance on top of high temp insulation. Marine Battery Cable is Class "I" stranding (super-flex) tinned copper. As good as you can get.
 

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I'm selling EIG 20AH Lipo cells for $1.50/AH OBO. I have 90 of them. They have all been tested and placed in manufacturers recommended storage voltage (3.8V). I have all the details for them and can printout discharge curves and provide all pertinent information.

I also have about 200 Turnigy 8AH cells. Only about half have been tested and placed into storage.

Let me know if you are interested.
[email protected]
 

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If LiPo, how can they be made to work at 12V for a House bank?
They cannot and is of no concern for scum bag spammer. LiPo is the last thing you want for a house battery or any application requiring long life as LiPo only have roughly 100 cycles in them. LiPo's are used in RC aircraft where C-Rates run 20C or greater continuous. Extremely dangerous lithium batteries notorious for catching fire.



They do have a application in EV used as Drag Racers where you can put a very small battery in, just enough for 1 or 2 runs. Some of the new ones claim 100C-Rate for 10 seconds which is all you need for a drag race. A 20 pound battery vs a 1000 pound battery.
 

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None of the lithium chemistries have nominal voltages high enough get away with three cells in series, and even the lowest-voltage common lithium chemistry (LiFePO4) runs at voltages which are too high to be ideal with four cells in series.

I know that my motorhome's furnace is not happy with the charging voltage for my lead-acid batteries; at the peak charging voltage for any lithium battery I would want a voltage regulator between the battery and most loads. I do understand that most people using LiFePO4 in RVs likely just run all loads at battery voltage.
 
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