LiFePO4 mobile charging

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gazzer
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LiFePO4 mobile charging

Post by gazzer »

I'm currently speccing my revamped RV (Motorhome).
200aH battery pack at 12v that comes with a 20amp charger/equaliser.
I understand that direct charging from from the RV alternator is not recommended (the usual way, split charger means) for LiFePO4 batteries.
My solution is a "large" sine wave inverter with at least 3 240v, possibly 4-6000w output.
If the alternator feeds the inverter as well as the RV battery (via an isolator switch if necessary) to the LifePO4 batteries via the 20amp charger/equaliser this should protect the leisure batteries.
PS there will also be at least 300w of solar input (roof space limit).
On parking up, the RV battery can be isolated and the internal 240v activated by the same inverter, (it's only required for the fridge, phone charging and the occasional fan on a hot day, oh and the IPTV box and screen).
I'm asking I suppose, is the inverter a suitable substitute to charge the 20amp charger signal?
There IS an external 240AC input connection but the availability could be erratic. That's no problem to sort.
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raysun
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Re: LiFePO4 mobile charging

Post by raysun »

Hmmm... it sounds out of balance to me.

First - a 12V 200AH battery is 2.4kWH of capacity. If depleted to 20% SoC, about 2kWH of charge would need replacing (160AH). The 20A charger would take about 8+ hours to recharge the battery.

A 6kW inverter, assuming it would be powered by the 12V lithium battery, could exhaust battery reserves in about 15 minutes. Actually, the 500A draw would kill a 200AH battery in very short order. Assuming the battery could safely discharge at a C1 rate, the maximum inverter size would be roughly 2400W. The battery would provide about 45 minutes of power before needing to be cut off.

The 6kW inverter could be run at lower loads, of course, but the efficiency goes way down. This large an inverter is a poor choice for the battery size.

The 20A charger needs 240W to operate. If using an inverter to drive it, a small inverter (1kW or less) would be best. However, converting mechanical energy (motor/alternator) to 12V DC (vehicle battery), to AC (inverter), then back to 12V DC (battery charger) is a chain full of losses. Doing so for 8 hours is impractical.

The "house" loads mentioned will be in the 1.5 - 2.6kWH range for daily consumption. The battery is going to be drained to its maximum on many occasions.

The 300W of PV will carry some of that load, but is so variable depending on location and weather, its hard to predict how much.

Bottom line, a better plan with more realistic equipment sizing is needed.

Starting with the 2.4kWH battery. Find its maximum rated continuous charging specs, and size the charger for that.

Determine the battery's maximum continuous discharge specs, and size the inverter at, or preferably, well below that.

Get a good handle on the actual "house" loads consumption and factor usage into battery discharge/charge plans.

Spec out the PV array, and combine it with a good quality programmable MPPT charge controller. I'd seriously consider building some sort of modular ground-mount PV array that could be deployed in the sun and used to contribute more to battery charger / daytime "house" loads service. I'd think a roof mounted array would have limited utility unless one is parked in the desert with no trees around. Otherwise, most of the caravanners I see tend to park in shade to keep their tin boxes cool on sunny days, just about the opposite of good placement for PV harvest.

Good luck!
gazzer
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Location: Malaga, Andalucia, SPAIN

Re: LiFePO4 mobile charging

Post by gazzer »

Thanks for coming back raysun.
My info in the post was a bit sketchy really.
The RV is for days away as opposed to living in.
That means there will be plenty of engine running therefore power from the alternator.
The 6000w quoted was "peak load", so constant use of 3000w. I don't ever envisage using that amount (nothing onboard that would use it), it's just there just incase.
The fridge is 3 way (12v/240v/gas) so when parked up gas will be the preferred option.
Most charging of electricals will also be done on the move. Phones and laptops will last overnight.
LED TV will only draw 50w and the IPTV box 10w. I don't think we will be glued to that for hours on end.
Space and weight balance are the issue on the RV and I am limited to a 200aH lithium pack, which, supplied by the manufacturer, is a 20amp charger.
I get what you say about shade and 300w roof mounted solar panels. Mainly they will aid charging en route but of course thru an MPPT charger.
Water heating and ambient heating is by gas and diesel respectively
We live in a 4.5 hour average sun region in southern Spain.
Cheers.
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raysun
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Re: LiFePO4 mobile charging

Post by raysun »

gazzer wrote: Tue Feb 09, 2021 12:45 am Thanks for coming back raysun.
My info in the post was a bit sketchy really.
The RV is for days away as opposed to living in.
That means there will be plenty of engine running therefore power from the alternator.
The 6000w quoted was "peak load", so constant use of 3000w. I don't ever envisage using that amount (nothing onboard that would use it), it's just there just incase.
The fridge is 3 way (12v/240v/gas) so when parked up gas will be the preferred option.
Most charging of electricals will also be done on the move. Phones and laptops will last overnight.
LED TV will only draw 50w and the IPTV box 10w. I don't think we will be glued to that for hours on end.
Space and weight balance are the issue on the RV and I am limited to a 200aH lithium pack, which, supplied by the manufacturer, is a 20amp charger.
I get what you say about shade and 300w roof mounted solar panels. Mainly they will aid charging en route but of course thru an MPPT charger.
Water heating and ambient heating is by gas and diesel respectively
We live in a 4.5 hour average sun region in southern Spain.
Cheers.
For comparison, we run two houses with two refrigerators, two freezers, lights, electronics, etc. with a 3kW inverter.

Its doubtful 3kW of peak power would be used, or could be sustained, by a typical RV alternator and a 200AH battery.

3kW / 12V = 250A. The battery would need to provide 250 amps of instantaneous current, and the alternator would need to support that output while the engine is running. Is that feasible?

Personally, I'd take a hard and realistic look at the practical maximums of the battery / alternator, and design the system around that.

Having an overly large inverter running at low power guarantees it will be inverting at low efficiency, likely well under 50%. A 100W load will draw more than 200W off the battery. Sizing the inverter such that the average load is nearer its maximum output will bring efficiency up into the 80-90% range, depending on the quality of design. Were I to look for maximum efficiency from my battery / inverter system, I'd look into the small Victron inverters that can stacked in parallel for greater output. The Victron Multiplus series may be a good candidate.
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Re: LiFePO4 mobile charging

Post by sbrownian »

I am amazed at the Radians' ability to basically shut almost down with extremely low AC loads. An inverter capable of 12,000 watts instantaneous only drawing 40 watts at standby?

An Excellent design job.
raysun
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Re: LiFePO4 mobile charging

Post by raysun »

sbrownian wrote: Tue Feb 09, 2021 11:10 am I am amazed at the Radians' ability to basically shut almost down with extremely low AC loads. An inverter capable of 12,000 watts instantaneous only drawing 40 watts at standby?

An Excellent design job.
Yes, the standby modes of many inverters is impressive. An FXR series in Sleep mode draws 4 watts.

However, that's not the case when AC is called for. A quick check of the typical output / efficiency curves shows very poor efficiency at low output power levels. Its a phenomenon we all live with, and largely ignore. That 12kW Radian putting out 100W AC is drawing far more than 100W DC from the battery.
sbrownian
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MUCH more efficient!!
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Re: LiFePO4 mobile charging

Post by sbrownian »

FWIW department:

Right now, the Radian is showing 1 amp per leg, so +200 watt-ish.. (Granularity is 1 amp.)
Solar is producing 290, plus drawing about 1 amp from the battery at 51.1v
So, roughly 340w DC for 200w AC out, as expected.
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Re: LiFePO4 mobile charging

Post by JRHill »

raysun wrote: Tue Feb 09, 2021 10:40 amFor comparison, we run two houses with two refrigerators, two freezers, lights, electronics, etc. with a 3kW inverter.
We have a similar dispersion of loads. I had pondered playing with a sleep mode but I just didn't see a sleep mode as useful. Like having various low draw devices shut down and have to be reset like the microwave, the satellite internet and TV, etc. And then there are the freezers and fridge firing up and bringing the inverter out of sleep mode constantly and without pattern. As I pondered, it sounded like a whole lot of manual stuff and probably a negative advantage.
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Re: LiFePO4 mobile charging

Post by raysun »

Yes, I don't use sleep. Its not worth it, and wouldn't actually sleep on my system, so why bother? The idle mode of the 2nd inverter in the parallel stack essentially sleeps that one anyway.

For a cabin that's used only periodically, or an RV, it might be worth investigating, especially if there are systems, like a water circulator to keep pipes from freezing, that should be run on occasion.
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Re: LiFePO4 mobile charging

Post by KeithBriggs »

I agree. Interestingly all the programming they have done with stacked radians. When a new load fires up, another 4k inverter clicks on and if not needed clicks back off a few seconds later. When you are using say 6000w, 3 of the 4 inverters in my case are handling 2k each I guess so they can be ready for additional loads if they come along. From an efficiency standpoint, I would think that it would be better if just 2 of the 4 4k inverters were on doing 3k each. Things I suspect I'll never understand. You get a lot for your money with the inverter. Not so with their combiner boxex (for another thread).

1000w microwave, 1500w hair dryer. Everything else is pretty minimal. I skimmed it but didn't see if you wanted to run A/C. That makes a difference! 3k inverter seems more than adequate.

These radians must have some beefy capacitors inside waiting to burst forth energy.
gazzer
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Location: Malaga, Andalucia, SPAIN

Re: LiFePO4 mobile charging

Post by gazzer »

S'funny, there is a guy who videos on U Tube for mobile use on a RV who has 200aH of lithium batteries, 2 compressor fridges and a shed load of other stuff, he uses 90aH per day and can recharge withing a few hours (inc solar) via Victron MMPT and DC/DC units and has no issues for up to 3 days without sun/engine. I don't have anywhere near that consumption.
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raysun
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Re: LiFePO4 mobile charging

Post by raysun »

gazzer wrote: Fri Feb 12, 2021 12:38 pm S'funny, there is a guy who videos on U Tube for mobile use on a RV who has 200aH of lithium batteries, 2 compressor fridges and a shed load of other stuff, he uses 90aH per day and can recharge withing a few hours (inc solar) via Victron MMPT and DC/DC units and has no issues for up to 3 days without sun/engine. I don't have anywhere near that consumption.
90AH @ 12V is roughly 1kWH consumption. The total battery @ 200AH × 12V is 2.4kWH. Lithium can be fully discharged if one doesn't mind a short cycle life. Most prudent users restrict DoD to 80%, or in this case 2.4kWH x 0.8 = 1.93kWH.

Those must be some mighty efficient refrigerators. What brand/model are they? I have a bunch of neighbors who would love to run even on refrigerator for 3 days on 2kWH.
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Re: LiFePO4 mobile charging

Post by sbrownian »

U-Tube guy running 48v or higher?
It would be more meaningful to know how many kWh was being used...
gazzer
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Re: LiFePO4 mobile charging

Post by gazzer »

Unfortunately he does not specify his consumable equipment. Th Vid is for the battery and wiring arrangements.
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raysun
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Re: LiFePO4 mobile charging

Post by raysun »

gazzer wrote: Sun Feb 14, 2021 10:38 pm Unfortunately he does not specify his consumable equipment. Th Vid is for the battery and wiring arrangements.
I'd be interested in hearing his claims. Is there a link?
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Re: LiFePO4 mobile charging

Post by JRHill »

I have seen where some suppliers of automotive batteries are advertising LI for a direct FLA/AGM replacement. Also PHI states that they are a direct lead acid replacement. But to me its not that simple. For our home based systems there are very specific charging requirements for the swap over to LI. I haven't seen a lot of this but I am curious that a vehicle's stock voltage regulator is not a good match for LI - driving down the road and the LI battery is being held at 100%?!? Likewise I've seen that LI is getting more popular with RVers/mobile like in this article but they seem to be used with purpose fitted controllers and inverters.

I'm still curious about this with LI used as a starting battery.
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Re: LiFePO4 mobile charging

Post by raysun »

I'm still curious about this with LI used as a starting battery.
I see several manufacturers offering Lithium batteries meant for starting service. Their claim of "drop-in" lead acid replacement would need to include some manner of charging circuit compatible with the standard charging/voltage regulation systems found on internal combustion engines. That wouldn't be too hard to manage if a simple charging profile (e.g.: Constant Current until full) is employed. Float could be handled the same way, dialing back the float voltage accepted by the cells while allowing "standard" lead acid float voltages to cross the battery bus.

Since these systems are proprietary, I doubt if we'll see any of the manufacturers showing what's under the covers. The "proof of the pudding" will be the warranty.

I'm also curious how the Lithium starter units would handle the cold. No problem in Hawaii, but winter on the Columbia would make the batteries unchargeable unless there was some form of cell heater or other provision.

Once a solid electrolyte is perfected, I'd think Lithium would take over the starter world. Until then, IMO, its sort of "pays yer money and takes yer chance".
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Re: LiFePO4 mobile charging

Post by JRHill »

raysun wrote: Mon Feb 15, 2021 10:37 amI'm also curious how the Lithium starter units would handle the cold.
Raysun, excellent point. With my transition to PHIs they are inside - they couldn't survive outside. Likewise in the pickup but I have no reason to do so - this is mainly curiosity. Granted RVers are a different application but one would have to remove the batteries in storage below a given temperature which I think is standard regardless of battery type.
raysun
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Re: LiFePO4 mobile charging

Post by raysun »

JRHill wrote: Mon Feb 15, 2021 11:43 am
raysun wrote: Mon Feb 15, 2021 10:37 amI'm also curious how the Lithium starter units would handle the cold.
Granted RVers are a different application but one would have to remove the batteries in storage below a given temperature which I think is standard regardless of battery type.
True, the application is different, but a fully charged lead acid battery is perfectly fine in low temperatures, as the electrolyte specific gravity retards freezing. A lithium starter battery in place overnight in sub-freezing temperatures cannot be charged according to most literature.
gazzer
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Location: Malaga, Andalucia, SPAIN

Re: LiFePO4 mobile charging

Post by gazzer »

The charging aspect from the vehicle I acknowledge (as mentioned) which is why you have to use the provided charger to the Li batts even tho it is only a 20amp unit but heavier supplies are available. Relying on engine alternator direct charging is not recommended, probably due to the constantly varying charge/engine speed.
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raysun
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Suniva 330 watt panels (12 - 6 strings of 2 in series)
Hyundai 355 watt panels (6 - 3 strings of 2 in series)
Honda EU7000is gas fuel generator

Re: LiFePO4 mobile charging

Post by raysun »

gazzer wrote: Wed Feb 17, 2021 10:36 am The charging aspect from the vehicle I acknowledge (as mentioned) which is why you have to use the provided charger to the Li batts even tho it is only a 20amp unit but heavier supplies are available. Relying on engine alternator direct charging is not recommended, probably due to the constantly varying charge/engine speed.
A 20A DC charging circuit is 12V x 20A = 240W, or 1/3 Horsepower. Running the RV engine to use 1/3 HP for charging is pretty wasteful. Of course, the engine will be powering whatever the battery / inverter are not while the battery is charging, but at 100AH, that's at most 12V x 100AH = 1.2kWH, or 2 HP with conversion losses.

It might be more economical and ecologically expeditious to use a small portable gas inverter generator to charge and to back up house loads.
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