[Sunking]

Wire size calculations in aircraft get even crazier.

Stricter yes like NEC, and for good reason. Easy to hop out of an RV or EV on fire. Not so easy on a plane or boat.

What many on-line calculators fail to take into consideration is SHORT distances. They assume lengths of 15 feet or longer will be used. Many do not put a Fail - Safe check built-in to see if the wire can safely handle the current or not.

For example enter in 2-feet, 50 amps, and 3% loss and many sites will come back with 12 or 10 AWG. If you have experience in electrical power know immediately that is dangerous. Sure a 2-feet run of 12 AWG will have the resistance low enough so that the wire only losses .36 volts with 50 amps flowing. Trouble is it becomes a Space Heater and burns the insulation off the wire. You would know instinctively and from experience the minimum safe wire size for 50 amps using 105 degree Insulation is 6 AWG.


Now some on-line sites are aware of this and have put in the Sanity Check. Some learned the hard way when they got sued and had to replace someones home because they are incompetent pretending to be experts. I know this for fact because it happened on a Forum I moderate. Yes this forum can be sued giving inaccurate or false information.

So remember this. Wire size is based on the OCPD (Over Current Protection Device like a fuse or breaker) feeding the wire. If you have a 20-amp circuit, the minimum wire size must be 14 AWG or larger. Does not matter if the circuit only caries 1 amp. A OCPD only has one purpose and one purpose only, and that is to protect the wire connected to the LOAD side. It has no other purpose. They are not there or capable of preventing electrical shock or protect the utilization equipment. Only the wire and nothing else. That 3000 watt Inverter at 12 volts requires a 300 amp fuse and a minimum 250 MCM (aka 4/0) copper cable. Voltage drop of a short 10 feet is of no concern operating at 12 volts. On the same lines anything over say 15 feet because a huge concern using toy voltages like 12 and 24 volts. You could find yourself needing multiple parallel pairs of 750 MCM. Use a higher voltage and all that goes away or a lot further out before it becomes a problem.

Low Voltage + High Power = Fire Hazard. Anything over 500 watts is high power for 12 volts.

 

[sportcoupe]

Looking at heating for hot water and even the van air, I may need to abandon the want for an all electric camper and add propane to the requirements list. Much easier to find efficient solutions for propane hot water and propane air heaters, some even offer a combo unit that does both. That will make the electrical easier to design.

 

[Sunking]

Looking at heating for hot water and even the van air, I may need to abandon the want for an all electric camper and add propane to the requirements list.

I was wondering how long it would take you to realize that. I would not have an RV without propane to do the cooking, heating, refrigeration, and generator. That is why many come with Propane Tanks. Batteries are for lights and entertainment.

 

[sportcoupe]

I was wondering how long it would take you to realize that. I would not have an RV without propane to do the cooking, heating, refrigeration, and generator. That is why many come with Propane Tanks. Batteries are for lights and entertainment.

Yes but we wouldn't have innovation if people just followed what everyone else did. I'm no Nikola though.

 

[john61ct]

Looking at heating for hot water and even the van air, I may need to abandon the want for an all electric camper and add propane to the requirements list. Much easier to find efficient solutions for propane hot water and propane air heaters, some even offer a combo unit that does both. That will make the electrical easier to design.

Absofookinlutely. Just silly to fry eggs bake a cake or boil water with DC electricity.

Unless you're sizing the bank for aircon or propulsion anyway

 

[john61ct]

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.

I never charge 4S LFP higher than 14V, usually 13.8V.

Under load stays around 13.1-2 cutoff at 12V.

Avoid the shoulders, gain longevity, no need to balance.

Never came across a load wasn't just fine with that, much less V sag than lead for winches, huge inverters etc.

 

[brian_]

I never charge 4S LFP higher than 14V, usually 13.8V.

Under load stays around 13.1-2 cutoff at 12V.

Avoid the shoulders, gain longevity, no need to balance.

Never came across a load wasn't just fine with that...

Yes, that would be within the range typically used for lead-acid, and so not a problem for an RV. That does make LFP the only sensible lithium chemistry, unless voltage regulation is used for sensitive loads.

Does that voltage range give the nominal capacity, or some fraction of it?

 

[brian_]

Looking at heating for hot water and even the van air, I may need to abandon the want for an all electric camper and add propane to the requirements list. Much easier to find efficient solutions for propane hot water and propane air heaters, some even offer a combo unit that does both.

The other fuel solution is diesel, since both water and space heaters are readily available. It seems fairly common to go with only diesel and solar in expedition campers (perhaps due to fuel availability worldwide). That only makes sense if the van has a diesel engine (which this one presumably doesn't).

 

[sportcoupe]

The other fuel solution is diesel, since both water and space heaters are readily available. It seems fairly common to go with only diesel and solar in expedition campers (perhaps due to fuel availability worldwide). That only makes sense if the van has a diesel engine (which this one presumably doesn't).

I'm looking at Promaster due to cargo volume and other pros. You can't get diesel in it anymore. The Transit and of course Sprinter both offer diesels. It is something to consider for sure.

 

[john61ct]

Does that voltage range give the nominal capacity, or some fraction of it?

With big prismatics like CALB or Winston, and a good vendor (not trying to save money) actual capacity at vendor voltages (14.6V down to ?10.5?) has been higher than rated.

No significant AH capacity is gained at the top shoulder between 13.8-9 vs 14.6V, maybe 2-3%

And in daily use going below 12V gets dangerous, especially at low current lows. Maybe 10% sacrificed for longevity there.

But the cycles vs avg DoD curve rules, just like lead, so building in a Reserve say 30-40% in your sizing may double or triple lifetime.

Long as you don't murder them of course, a high risk over say ten years.

 

[Sunking]

I never charge 4S LFP higher than 14V, usually 13.8V.

Under load stays around 13.1-2 cutoff at 12V.

Avoid the shoulders, gain longevity, no need to balance.

I agree with this. For 12 and 24 volt LFP systems a BMS is just a waste of time and money, and will kill your pack. I do not even use one for 32S 96 volt pack in my golf cart. All successful Solar Systems I have designed do not use any BMS.


Just Bottom Balanced the cells, charge to 13.8 volts, and LVD at 12 volts. This really works great on solar systems because you just Float Charge the batteries and never disconnect panels. With a POS BMS, you have to terminate charge and disconnect the Solar Panels which is STUPID because if the batteries are charged by noon, you disconnect the panels and go on batteries while the Sun is still up and usable. All it does is kill the batteries faster. Let them Float and all you use is power from the panels and save your batteries for night and rainy spells.

Never came across a load wasn't just fine with that, much less V sag than lead for winches, huge inverters etc.

This part I do not fully agree with. LFP are drop in replacements for Pb, and no changes are required. However Chi-Com LFP batteries do not have the high C-Rates of a good lead acid, and there is no contest against AGM will run circles around any Chi-Com LFP. A Chi-Com LFP internal resistance is 2 to 3 times higher than than a Pb battery of same AH capacity. You can take say a 55 AH Optima Red Top and put it up against a 100 AH CALB, and the Optima will outperform the LFP with respect to voltage sag by a large margin. To get really low Ri would require you to buy a quality LFP cell from reputable manufactures like A123 Systems or LG Chem, but you will pay up some 400% to get them if they were available.

 

[brian_]

I'm looking at Promaster due to cargo volume and other pros. You can't get diesel in it anymore. The Transit and of course Sprinter both offer diesels. It is something to consider for sure.

Most companies building Class B and C motorhomes using the ProMaster went with the gas engine from the beginning, presumably for cost savings. All manufacturers have had challenges getting diesel engines approved and sold in the last few years, but I didn't realize that FCA had given up on diesel for the ProMaster. In the rest of the world this van (the Fiat Ducato) is diesel-only.

 

[Sunking]

Most companies building Class B and C motorhomes using the ProMaster went with the gas engine from the beginning, presumably for cost savings. All manufacturers have had challenges getting diesel engines approved

That you can blame on the Employment Prevention Agency. Last thing they want in the USA is efficient diesel engines. Go to about any other country in the world, and passenger car fleets are mostly diesel engines. They get much better gas mileage. If it were not bad enough the enough the EPA make sit almost impossible to pass ever increasing emission standards no manufacture can can keep up with, Those that do pass are forced to pass those cost on to consumers. For those manufactures that do offer diesel engine options in the USA, EPA has an answer for it by making refining requirements so high making diesel significantly higher price than gasoline so no one will buy the cars because the fuel is too expensive. The Employment Prevention Agency needs to go and be replaced. EPA is Nixon's last one finger salute to America, he gave us the EPA before he resigned and laughing at us now. He made it look like a Democrat program.

 

[sportcoupe]

Most companies building Class B and C motorhomes using the ProMaster went with the gas engine from the beginning, presumably for cost savings. All manufacturers have had challenges getting diesel engines approved and sold in the last few years, but I didn't realize that FCA had given up on diesel for the ProMaster. In the rest of the world this van (the Fiat Ducato) is diesel-only.

The US version of the promaster diesel had an automatic manual transmission. It was not successful (non-popular) and was problematic. That and the EPA went after FCA diesels in 2016 after it screwed Volkswagen over big time.

Transit has a diesel. I am thinking about it but the ecoboost V6 is a beast in the Transit. It would be hard to pass it up.

Sprinter is bring a gasoline version to the mix in 2019.

I will drive all three before making final decision.

 

[sportcoupe]

That you can blame on the Employment Prevention Agency. Last thing they want in the USA is efficient diesel engines. Go to about any other country in the world, and passenger car fleets are mostly diesel engines. They get much better gas mileage. If it were not bad enough the enough the EPA make sit almost impossible to pass ever increasing emission standards no manufacture can can keep up with, Those that do pass are forced to pass those cost on to consumers. For those manufactures that do offer diesel engine options in the USA, EPA has an answer for it by making refining requirements so high making diesel significantly higher price than gasoline so no one will buy the cars because the fuel is too expensive. The Employment Prevention Agency needs to go and be replaced. EPA is Nixon's last one finger salute to America, he gave us the EPA before he resigned and laughing at us now. He made it look like a Democrat program.

Partially because diesel fuel is much cheaper then petrol (gasoline) in most other countries. Also EPA restrictions installed for US market diesels makes them very complicated engines and expensive to fix. Example is DEF or diesel exhaust fluid and the regen system. Run out of DEF and you cannot just add more and drive, it needs reset by the dealer to even start the engine again in some cases.

 

[sportcoupe]

I've been researching and cannot find reasons to prohibit installing AGM (or even FLA) house batteries under the van as long as they are protected from impact hazards and away from excessive heat.

 

[Sunking]

Partially because diesel fuel is much cheaper then petrol (gasoline) in most other countries.

Correct and the EPA made damn sure Diesel in the USA would be higher by making refineries refine diesel more than other countries. All done to discourage deisel fuel use by design. That means the EPA does not care about efficiency and want to punish the citizens.

Also EPA restrictions installed for US market diesels makes them very complicated engines and expensive to fix. Example is DEF or diesel exhaust fluid and the regen system. Run out of DEF and you cannot just add more and drive, it needs reset by the dealer to even start the engine again in some cases.

Again intentional by design to keep diesels out of the country and punish those that can get in. Want a diesel engine. By a Dodge Ram Truck. No DEF required.

 

[john61ct]

I've been researching and cannot find reasons to prohibit installing AGM (or even FLA) house batteries under the van as long as they are protected from impact hazards and away from excessive heat.

Sure what do you think the problem would be?

Strong skid plate under!

 

[john61ct]

I agree with this. For 12 and 24 volt LFP systems a BMS is just a waste of time and money, and will kill your pack.

Well I see "BMS" not as a thing, but clusters of protective functionality.

The active cell balancing is not needed, and therefore its complexity violates KISS, Occam's Razor.

To be discussed further another time.

> Bottom Balanced the cells
By avoiding the shoulders doesn't really matter. In House use I don't go below 2.99Vpc, redundant protection there, and that is farther from the low shoulder than 3.45Vpc is from the top one, so I top balance

I don't like to Float, so if convenient once LFP is full I continue the charge source for carrying loads, just isolate the LFP and let the lead buffer and support loads if needed.

If that is too complex for the context, I drop float to 13.2, enough to keep SoC in place but nit stressful. If not actively cycling I keep SoC low, and 13.2 Float is also good for that.

> LFP are drop in replacements for Pb, and no changes are required.

On the load side maybe but not true for charging, if longevity is desired I ensure sources are user custom adjustable.

>However Chi-Com LFP batteries do not have the high C-Rates of a good lead acid, and there is no contest against AGM will run circles around any Chi-Com LFP.

No idea what that means.

Large prismatics from Winston/Thundersky/Voltronix, CALB, GBS, A123 & Sinopoly have no issues with multiple C-rate if needed.

I do not buy cheap LFP, here $700 USD is cheap per 100AH 4S, can be $900+ with shipping.

House rarely requires over .5C in my experience. In that neighborhood, and certainly higher rates, as SoC drops, voltage drops less with LFP than with lead at the same AH size.

Optima are no longer relevant to deep cycling use since Enersys sold them to JCI. Glorified Starter bat, good for winches etc as you say, but very poor cycle longevity.

Here AGM is very poor value, only install when the space requires sideways or access to add water is inconvenient.

 

[Sunking]

> Bottom Balanced the cells
By avoiding the shoulders doesn't really matter. In House use I don't go below 2.99Vpc, redundant protection there, and that is farther from the low shoulder than 3.45Vpc is from the top one, so I top balance

You have to pick one or the other, Top or Bottom. With Bottom Balance you Balance at 2.4 to 2.5 volts.



When Bottom Balance you set two known reference points.


Capacity = 0 AH @ 2.5 vpc. Makes it impossible to over discharge any cell. They all arrive at 2.5 volts at the same time with 0 energy in the cells so they cannot drive adjacent cells to reverse polarity and destroy themselves.



With Top Balance you only know each cell is at 100% SOC, capacity is unknown. As you discharge the weakest cell can easily fall below 2.0 volts while the others are at 3 volts or higher, and wil destroy the discharged cells. In other words you set yourself up to destroy the batteries by making it possible.



The real danger is 2.0 vpc. 2.5 is manufactures covering their butts. On a 4S system you would set LVD anywhere from 11 to 12 volts, well above 8 volts on a fully discharged 4S pack. To charge is simple. Set it to 13.8 volts and let them float until the cows come home. SOC will be in the 90's just before you reach the shoulder.



LFP are the most high voltage tolerant of all lithium batteries. They can be charged to 4.2 volts without much damage or risk of fire. But like any lithium battery will not tolerate over discharged, so stay clear of the bottom shoulder. You can flirt with the top shoulder if you do not mind sacrificing some cycle life to get that last 1 to 4% SOC, bu tthat means you are stuck inside a lead acid battery box using a lead acid BIBLE verse 1:


1. Thou Shall Charge To 100% or thy will be cast to hell in a crypt of hardened Lead Sulfate Crystals.