LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

[T1 Terry]

Originally Posted by Adamante

What would be the advantage of switching from the 144 V series combination to the 48 V parallel for extracting 12 V house power? In either case a DC to DC converter would be needed so why bother with the switching?

A 4kw inverter and all appliances are 240vac. No more paying ridiculous prices for half efficient products because that is all that can be used because of the 12v battery limitation.
Previously big inverters were not really an option because lead acid batteries lost a lot of capacity once the C20 rating was exceeded, the only way around it was to use a huge battery pack. Those days are over with Li batteries, they don't suffer the lost capacity effect.
There will be a DC to DC converter as well, linked to the 12v start battery to keep it charged and to power the LED lights and a few 12v appliances like the GPS and stereo but the major appliances are 240vac.
A fridge freezer for instance, just over AU$2,000 for a 221ltr Waeco fridge freezer or AU$550 for a 250ltr frost free auto defrost Fisher & Paykel. Aust govt energy and efficiency tested to operate in 40 Deg C and higher temps, the Waeco struggles above 32 deg C and burns a lot of battery power because they are running at or near 100% duty cycle in those temps.
A 1hp split system aircond in the bedroom will run all night from the battery bank so sleeping and mouldy clothes will no longer be a problem in the high humidity areas.

Things may be different on a boat with electrical safety issues but I’d imagine an RCD/RVD combination unit would keep things safe.

T1 Terry

[s/v Jedi]

Please stop this talk about 144V house battery banks and matching inverter/chargers etc.... I can barely control myself now and am afraid you guys are gonna push me into spending mode again...

ciao!
Nick.

[T1 Terry]

Originally Posted by s/v Jedi

Please stop this talk about 144V house battery banks and matching inverter/chargers etc.... I can barely control myself now and am afraid you guys are gonna push me into spending mode again...

ciao!
Nick.

The 144v is for propulsion not as a house battery bank. The 3 X 48v house battery banks are switched from parallel connection to series connection to create the 144v. The number one 48v pack remains tied to the inverter and the DC to DC converter, the other two 48v packs switch.
It could work well for someone looking at pulling the diesel propulsion motors out and fitting electrics and mounting one of the diesels in a better position as a gen set.

T1 Terry

[Adamante]

Using 240 V AC appliances instead of 12 V DC is a very sensible approach. I plan to do the same, but at the 120 V AC level.

However, that still doesn't explain why you are switching your battery connection to a 48 V DC parallel configuration to run the 4 KW inverter. Why not run the inverter directly from 144 V DC?

[s/v Jedi]

Originally Posted by Adamante

Why not run the inverter directly from 144 V DC?

Exactly, why consent with that dull old 48V stuff. I was serious mentioning 144V house banks!

cheers,
Nick.

[bill good]

But them 4KW inverters for grid power are about $1/watt ie $4000.00. Also they want a lot more than 144vDC. getting into danger zone!!

Bill

[T1 Terry]

Originally Posted by bill good

But them 4KW inverters for grid power are about $1/watt ie $4000.00. Also they want a lot more than 144vDC. getting into danger zone!!

Bill

Exactly, a lot harder to recharge as well. A 48v 4kw inverter with built in soar controller and 50amps mains battery charger with the voltage levels reset to suit Li batteries was AU$980 including freight. Anything above 125vdc is heading into dangerous lethal territory, switch these voltages is trick business requiring capacitor precharging among other things and becomes a specialist type build. Overkill for house power but a necessary evil for electric propulsion if you need to make big kw's and torque.

T1 Terry

[witzgall]

I will give you all the back story sometime soon, but in the meantime, it looks like I will have the opportunity to install a 16 cell, 800ah 12v LIFEpo4 bank on our boat, taking up the space of our 4 t-105 trojans, and weighing about the same. To do this, I imagine I will need to wire them up as 4, 3.2 volt banks, each comprised of four, 200ah 3.2v cells. My two battery boxes are back to back, with space for two banks in each one. So the individual cells would be connected to each other with bus bars, and the two adjacent cells would be attached to each other with (hopefully) bars as well. But the two, resulting 6v cells would need to be attached to each other with cable, and I am unsure as to what size I would need, or if this is even safe, as the currents these two cables could carry have the potential to be huge!

The reason I wish to do it this way, instead of just making up four, 200ah 12v banks and them connecting them in parallel, is that I have a single BMS system, designed to attach to a 4 cell 12v system.

Should I look into getting another BMS, is that the better way?

Chris

[s/v Jedi]

Originally Posted by T1 Terry

Anything above 125vdc is heading into dangerous lethal territory

Actually, it is current that kills, not voltage. 48V DC is often considered the upper level before it becomes dangerous (which is why 48V is used so often) but I read about a case of electrocution at 42V DC so 48V is still not 100% safe.

If one is scared of voltages above 48V then you can't have AC anymore as the world uses 110-250V. It is a mistake to think that 220/230V is more dangerous than 110V: statistics of cases of electrocutions show that.

The issue of cost is something else... 48V DC equipment will be better priced and I agree it's a big step beyond the 12V systems most boats are handicapped with now.

ciao!
Nick.

[Paul L]

What length and type of warranty are vendors giving on LifeP04 batteries when used in a marine environment?

[bill good]

The higher the voltage the further the arc can be apart this is why the DC house power was found to have caused a lot of fires in the years past!! AC going thru zero voltage which did help put the arc (fire) out. To protect the batteries a current limiter type of fuse could be used as a link between the cells without the need of an external mounted fuse. The advantage of AC is to do with the distribution.

[Adamante]

Originally Posted by T1 Terry

A 48v 4kw inverter with built in soar controller and 50amps mains battery charger with the voltage levels reset to suit Li batteries was AU$980 including freight.

Aah, so it’s the cost of the 144 V inverter vs. a 48 V inverter. That makes sense.

I see 144 V inverters sell for about $2,500, so you are trying to save around $1.5K. Saving money is good - if you can make it work.

But is it practical? For your switching scheme to work you have to add more power cable wiring, switches, and relays with contactors capable of handling the motoring currents. This type of equipment will not be not cheap. So you would be adding cost, complexity, a need for additional maintenance and creating the possibility of additional points of failure in the system.

You will also have an unbalanced load on your battery pack. If I understand your scheme correctly, the inverter will be normally powered by the parallel combination of the three battery banks. When you switch to motoring, two of the banks will see only the motoring current draw, but the third bank will also be seeing the inverter draw (and the DC/DC converter). So the three banks will be discharging at different rates. What do you do when pack one reaches 80% DoD while packs two and three are at 50%? How do you monitor and manage that so you don’t kill one of the banks? I’m sure it can be done, but I suspect again at an additional cost and complexity.

Since the first bank will be cycled (charge, discharge) more often than the other two banks, you will have batteries at different points in their life cycle. This would of course depend on the frequency of the bank one cycling, but I would guess that if you are long- term cruising, bank one will be cycled at least once per day. Maybe not a huge factor given the life cycle estimates for LIFEPO , but still this inserts a dynamic variable into the system that needs to be managed.

How do you plan to implement the charging scheme? I assume you will have a 48 V DC charger to charge the parallel bank off the genset, solar, or shore power. How will you charge the batteries while motoring? When your batteries are in a series combination, your 48 V DC charger will only be able to charge one of the three banks. What about the other two banks? Or will you have another 144 V DC charger running off the genset to charge the whole string at one time? Again, added cost and complexity.

I have not seen this type of a complex powering scheme proposed for a boat before. It doesn’t mean it can’t be done or that it’s not a good idea. I suspect that you have thought all this through more than I have, so it would be helpful if you could address those questions.

[T1 Terry]

Originally Posted by witzgall

I will give you all the back story sometime soon, but in the meantime, it looks like I will have the opportunity to install a 16 cell, 800ah 12v LIFEpo4 bank on our boat, taking up the space of our 4 t-105 trojans, and weighing about the same. To do this, I imagine I will need to wire them up as 4, 3.2 volt banks, each comprised of four, 200ah 3.2v cells. My two battery boxes are back to back, with space for two banks in each one. So the individual cells would be connected to each other with bus bars, and the two adjacent cells would be attached to each other with (hopefully) bars as well. But the two, resulting 6v cells would need to be attached to each other with cable, and I am unsure as to what size I would need, or if this is even safe, as the currents these two cables could carry have the potential to be huge!

Originally Posted by witzgall

The reason I wish to do it this way, instead of just making up four, 200ah 12v banks and them connecting them in parallel, is that I have a single BMS system, designed to attach to a 4 cell 12v system.

Should I look into getting another BMS, is that the better way?

Chris

Hi Chris,
The size of the connecting cable is determined by the number of amps you wish to pass through it and the length of the cable. This one gets tricky because it's actually 6v you are trying to pass from one battery bank to the other, the lower the voltage, the higher the amps, the bigger the cable needs to be to minimise voltage drop. Many electricians work on a 5% voltage drop being acceptable but 5% at 6v 2% is even a bit much.
If the distance between the two 6v battery banks required a cable roughly 15ft long it would need to be 000AWG or bigger to carry 200amps and there would be losses, if the two banks were each 12v even though 2 cables would now be required using the same 200amp figure the losses would be negligible.
If you are willing to run 2 parallel 000AWG cables between the 2 6v battery banks then this is probably the better way to go because any imbalance between the cells is counteracted by another cell within each 3.2v unit. If a cell fails for any reason a voltage drop would be quickly seen in that cell group, the bad cell located and isolated and the battery pack brought back on line with just a 200ah loss of capacity but no loss of current supply capability. In other words, every thing would run as normal but more frequent recharges would be required till a replacement cell could be found and fitted.
Two 12v packs running in parallel would require 2 BMS units, the same amount of cabling but more of a chance of imbalance between the two 12v packs and less cell self balance but as a plus, the system could remain up and running while you isolated the battery bank with the crook cell, tested and removed that cell. A good BMS with HVC and LVC would be needed to protect the individual cell that would be running in that bank but it's a do-able, just cost more.
Each method has it's advantages and disadvantages, $$ and complexity is the real deciding factor.

T1 Terry

[T1 Terry]

Originally Posted by Adamante

Aah, so it’s the cost of the 144 V inverter vs. a 48 V inverter. That makes sense.

I see 144 V inverters sell for about $2,500, so you are trying to save around $1.5K. Saving money is good - if you can make it work.

But is it practical? For your switching scheme to work you have to add more power cable wiring, switches, and relays with contactors capable of handling the motoring currents. This type of equipment will not be not cheap. So you would be adding cost, complexity, a need for additional maintenance and creating the possibility of additional points of failure in the system.

You will also have an unbalanced load on your battery pack. If I understand your scheme correctly, the inverter will be normally powered by the parallel combination of the three battery banks. When you switch to motoring, two of the banks will see only the motoring current draw, but the third bank will also be seeing the inverter draw (and the DC/DC converter). So the three banks will be discharging at different rates. What do you do when pack one reaches 80% DoD while packs two and three are at 50%? How do you monitor and manage that so you don’t kill one of the banks? I’m sure it can be done, but I suspect again at an additional cost and complexity.

Since the first bank will be cycled (charge, discharge) more often than the other two banks, you will have batteries at different points in their life cycle. This would of course depend on the frequency of the bank one cycling, but I would guess that if you are long- term cruising, bank one will be cycled at least once per day. Maybe not a huge factor given the life cycle estimates for LIFEPO , but still this inserts a dynamic variable into the system that needs to be managed.

How do you plan to implement the charging scheme? I assume you will have a 48 V DC charger to charge the parallel bank off the genset, solar, or shore power. How will you charge the batteries while motoring? When your batteries are in a series combination, your 48 V DC charger will only be able to charge one of the three banks. What about the other two banks? Or will you have another 144 V DC charger running off the genset to charge the whole string at one time? Again, added cost and complexity.

I have not seen this type of a complex powering scheme proposed for a boat before. It doesn’t mean it can’t be done or that it’s not a good idea. I suspect that you have thought all this through more than I have, so it would be helpful if you could address those questions.

I'll try to start from the top and work down.
It's not only the cost of a 48v inverter V 144v inverter, there is a charger as well and ease of obtaining a replacement or fixing the fault. The 48v inverter/charger/solar regulator I'm trialling is a card based unit. A few test points will determine what card failed so spares could be carried if the inverter was a life and death issue.

I'm guessing the cabling wouldn't be an issue, to make up a 180ah 144v battery bank would require the pack to be broken up to better distribute the weight. Isolation would also be required between packs for the purpose of maintenance so it's just a different type of switching relay rather than no relay at all.
The unbalanced load on the No.1 battery pack would be partly offset by it being the only pack being charged by the 48v charging system. In my case that will be 1kw of solar but it could be an alternator in a hybrid assist set up or the whole 144v pack charged by a gen set.

In the case of an out of balance between the 3 packs a simple switch back to parallel connection will again balance them. I expect the no.1 pack will cycle more but not between the fully charged and 80%DoD but rather in the middle range. There is no data regarding the effect of this but a number of informed sources including Jay Whitacre from the Carnegie University suggest that this intermediate state cycling has no real effect on cycle life so it can virtually be ignored. The practical results are yet to be tested but with a 3,000 cycle life to 80% DoD it will take 8 yrs or more to see who's right or wrong.

My case is a lot different to a boat application as it's in a motorhome so my recharging while in series mood will be via regenerative braking. As it will be a hybrid set up it will double as a genset if required.
In a single drive set up in a boat I can see this system working quite well, the electric AC motor connected to the prop shaft with the diesel engine coupled with a dog clutch behind the electric motor. When more grunt is needed or regen required or steaming for a long period a combination of the two units could be used but in general for manoeuvring in or out of a mooring etc simple electric propulsion with switchable reverse would be the ideal set up.

Hope I didn’t miss any bits, naturally this is a hypothetical system I'm looking at for a boat application so lots of fine tuning would be needed but I think it would work well.

T1 Terry

[OceanPlanet]

Originally Posted by T1 Terry

Now there's a problem that I hadn't thought about but obvious now you mention it, the shade from sails. I guess the panels are separated in the best vantage positions around the boat so inter connected wiring in series with a single controller wouldn't be a logical move so your system is tailored to suit sailing boats in particular.
Each system has it's own set of problems, on a motorhome it's aerials, satellite dishes vent hatches, roof top airconditioning and trees in all the best camping spots :lol:
Do boats more rely on generator charging and solar as a top up? Do many use wind or water driven turbines?

920ah @ 24v, that is a serious system, is it for propulsion or just house power? I guess air conditioning would be run off a system that size because the near zero Peukert’s factor of Li cells would make that more efficient than an engine driven unit.
Thought about the controller per panel idea but the cost would be prohibitive on my type of set up, too many panels. Ultimately the final plan for my system is 3 X 48v 180ah Li battery pack that can be switched from parallel for house power to series to provide 144v nom for a hybrid drive set up with regen braking and solar for recharging.

T1 Terry

T1, Yep house banks. In this case it is WAY overkill for the boat's loads but the rules have a minimum battery weight. So their capacity is so much that for some legs they don't need to charge at all (bring less fuel, be lighter, go faster....). Very cool plan you have for hybrid drive! Will you be posting info on that on some other site? Ok to PM me off this thread...we're getting way off the track...;-)