Electric Barge Battery Bank

a_little_knoladge

Hi all, would just like your thoughts on if this duel voltage DC battery bank will work, in theory I believe it should! If you can see any problems I may encounter please try and clearly outline them and it would be appreciated if opinion was kept out of any feedback, much appreciated. Below is a link to the battery bank diagram:

https://imgur.com/a/JvEvBUL 

The battery bank is designed for an electric barge, to supply both house loads and for propulsion power. Each 24v battery is a used tesla 5.3Kw battery pack with is own BMS (non OEM). The 48vdc side will power all the house loads through an 8Kw inverter/charger. Charging will be done on the 48v side by either of the following:  7Kw solar array, mains hook through the inverter/charger (200 amp charger) or as backup a 5Kw DC generator.  

The 250vdc side is there only to power the twin electric motors 55Kw-110Kw each, large power range due to potential weight saving on more powerful motors full power output will be controlled by each motor controller and calculated along with house at full load to ensue its within the batteries C rating. 

apologies in advance if I missed any crucial information, look forward to you thoughts. 

cheers 

Photowhit

a_little_knoladge said:

Hi all, would just like your thoughts on if this ...

a_little_knoladge said:

...and it would be appreciated if opinion was kept out of any feedback, ...

Haha...

Marc Kurth

What is your daily Kwh design load for the propulsion system and house inverter?

a_little_knoladge

What is your daily Kwh design load for the propulsion system and house inverter?

Hi Marc Kurth, I have calculated an average of between 6-9Kwh daily for house loads depending on the time of year. 80Kwh daily propulsion power usage is based on the max silent cruising range I would like to have. This gives me 8 hours of silent cruising and the average 6-9Kwh in house loads without the bank dropping below 15% depth of discharge. This is not taking into account any solar generation. 

Sorry Photowhit Solar Expert let me clarify, I would like fact based input on the viability of the set up not opinions on if i should do it like this or not. 

cheers

Marc Kurth

a_little_knoladge said:

What is your daily Kwh design load for the propulsion system and house inverter?

Hi Marc Kurth, I have calculated an average of between 6-9Kwh daily for house loads depending on the time of year. 80Kwh daily propulsion power usage is based on the max silent cruising range I would like to have. This gives me 8 hours of silent cruising and the average 6-9Kwh in house loads without the bank dropping below 15% depth of discharge. This is not taking into account any solar generation. 

Sorry Photowhit Solar Expert let me clarify, I would like fact based input on the viability of the set up not opinions on if i should do it like this or not. 

cheers

It would seem to me that you have 10 batteries at 5.3 Kwh each = 53.3 Kwh of total storage. What is that I am missing?

Sorry, I know that you asked for no opinions, but..........

BB.

I am also a bit confused about your 250/48 VDC bus wiring... Are you trying to get both from the "battery bank" at the same time using all of the batteries to power both 250/48 VDC at the same time? (does not look like there are separate isolated charging ports for the Tesla packs on your drawing???)

Generally, you cannot do that. You can series/parallel for 48 volts, or series/parallel for 250 volts at one time. And if you have a 250 Volt string, and want to "tap" 48 volts from the first two battery packs, you can do that... But this creates issues too... You are pulling current from 2x of the battery packs, and discharging those two. And you are using the same packs for 250 VDC, and that is reducing the AH/kWH capacity of the whole bank (i.e,. your bottom 2x 24 volt packs will at some point be near zero stored energy, while the rest of the high voltage packs still have more stored energy. A BMS would disconnect the two low 24 VDC packs--And shut down your entire 250 VDC bank.

If I am understanding this.

And as Marc asks, you seem to be looking for ~90 kWH per day from a bank that is 20 x 5.3 kWH = 106 kWH bank? Does not leave a lot of room for error (onboard gensets I guess, and a 7kW solar array?).

I am guessing you are looking at 20x 24 VDC battery packs, and not something different (from the drawing).

There are other issues too... Like charging at 240 VDC and 200 Amps (or was that intended to be 24 VDC at 200 amps)?

More or less, you are looking at electric car/truck power levels and technology. I am not familiar with what is out there--But there is some pretty amazing power components out there...

Is this intended for personal use, or need to be USCG approved as some sort of commercial vessel (might be difficult with custom Li Ion and power electronics)?

I would also look at how stable the barge is vs the 7 kWatt array... That is a lot of "sail area" if you have gusty weather/afternoon thunderstorms (somewhere in Florida?).

I would back up a moment and look at your energy needs, vs trying to marry the Tesla + Load requirements up front. There are a lot of details that need to be worked out first (from what I can see)....

-Bill

petertearai

https://www.nzherald.co.nz/nz/news/article.cfm?c_id=1&objectid=12044472
Kind of a barge . But not solar .

Marc Kurth

Bill, good catch - I have trouble counting! It is indeed 20 batteries for 106 kwh. The 48v bus is connected to all of the batteries.

mcgivor

Very interesting concept scavenging 48V from an otherwise 250W bank, the one issue that would need to be addressed is the protection, or lack there of in the 250V portion. As each 48V pair has a BMS to protect from overcharge, over discharge etcetera, what would prevent the 250V load from over dischargeing the entire bank where the collective BMS's have no control.

That could perhaps be done with some sort of voltage monitoring, but that would have to include each 48V cell/battery in the 250V arrangement as the capacity of each will differ to some degree, or in other words a BMS which see a cell (cell block/battery ) voltage of 48V in a  1P 5S  × 2 configuration, the downfall of that though would be no individual cell block, or individual cells, have protection within the individual modules. 

Obviously this is something that would need to be custom made, the difficulty is that each Tesla module is made up of hundreds of individual cells forming cell blocks, each cell with an individual fuse, this allows a single cell, or cells to disconnect which  may be detectable at the 48V level via the BMS but extremely difficult at the 250V aggregate.

Just some thoughts, not opinions, which may, or may not help, I do appreciate  the way you're thinking and reaching out for input, that can be constructive in your quest, unfortunately opinions are also helpful, ypu just need to filter out the negativity at your discretion.

a_little_knoladge

Thanks guys, Marc Kurth, petertearai, BB. appreciate the input please read all post carefully, took me a while to get my head around it, and I thought it up!

Each green box with 24v written inside it is a 24v 5.3kw battery pack, there are indeed 20 batteries equaling 106Kw.

The 48v system consists of 10 packs, 2 batteries in each connected in series, utilises the 250vdc series connections to produce 48v in every 2 battery packs, they are then paralleled to the 48vds bus, as all batteries are connected this should avoid uneven discharge assuming all connections have the same resistance. 

The 250vdc (I say 250v as nominal voltage of this packs is 25v+) side consists 2 packs of 10 batteries in series that are then paralleled to the 250vdc bus. 

Required silent cruising range plus house loads would indeed be just under 90kwh depending on the time of year, this  would not drop the battery below 15% depth of discharge, which from all of my research into these tesla packs would be perfectly safe and do no damage to the batteries. This is assuming no solar generation during 8 hours of cruising. 

I am in the UK I write on this forum as you lot in American tend to do bigger projects. There are requirements and inspections that have to be done, nothing to stringent though, the wording is "done by a competent person" think I have that covered been a marine engineer myself.

The solar array would have no windage as they will be mounted static and flat, and is size to UK average seasonal weather patterns hence the size! 

Slightly larger than that petertearai, try google widebeam barge. 

BB.

I have watched a couple of "narrow barge" TV shows from the UK... Still a good number of canals out of the from 100-200+ years ago before trains/roads/trucks became the main mode of transport. Basically cruising on canals at ~3 mph or so. Beautiful area, rebuilt a large part of the system (canals, locks, etc.). in the last decades. Not much in the way of bulk transport in the interior canal system any more(?).

I am still trying to understand the 48 VDC pair of battery packs, and combining them all into a ~240 VDC (nominal) battery bank.

The only way you can pull 48 volts 10x from a 240 VDC battery bank is if each battery pack as two outputs. One a 24 volt (in this case) DC bus to the batteries. And a second isolated output of 24 VDC (through a galvanic isolated (bi-directional?) DC to DC converter).

There is no way to pull via simple copper wiring both 240 VDC and 48 VDC from the same bank (except from two packs at one end of the 240 VDC string).

If I understand correctly your wiring--You cannot connect your 20 packs in both series (240 VDC) and parallel (48 VDC) to a single +/- battery pack pair of +/- 24 VDC connectors. Doing that will short out the 240 VDC wiring.

The only way to pull both 240 VDC and 48 VDC from your 106 kWH battery bank is to wire up for 240 VDC series (prime power for motors) and use a DC to DC down converter for 48 VDC power... Or wire up for a 48 volt bank and use DC to DC converter(s) to up convert to 240 VDC nominal for the prime mover motors. (or run 48 VDC motors directly, etc.).

I have not research the Tesla (or other commonly available BMS battery management systems). Depending on the BMS functions (monitoring, actual control/cutoff, etc.), you will have other limitations too.

-Bill

a_little_knoladge

Hi mcgivor thanks for the input, I was planning on the BMS on the 48v side also having the ability to low voltage disconnect the 250vdc loads or sound an alarm haven't decided yet, this will protect the battery from over discharge. The BMS's I will be using monitor a string of individual cell, can't remember how many, but they are able to detect losing an individual cell, If individual cells fuses start burning then the BMS hasn't been doing its job or the cell has gone bad anyway hence the Tesla design. 

Cheers BB if you have a look at the diagram below hopefully can clarify things for you. 
https://imgur.com/96kkUGV 
Try looking at them as two completely separate systems that happen to share some "wiring" 
Could you please show me where there is a short on my diagram. 

a_little_knoladge

Hi guys I must apologies there is a mistake in the diagram I posted, I will do another corrected diagram asap. 

BB.

No problem. We are here to help be a second pair of eyes at times.

-Bill

mcgivor

@a_little_knoladge Been thinking about your system design with the 48V / 240V combination and a few things came to mind in the form of questions. Have you considered using a 240vdc to 240vac inverter for house loads, thus eliminating the need for 48V altogether? Do you currently have the propulsion motor, or is that something that is under consideration?, rationale behind the question is there are frequency drives which convert 240vdc to 3 phase  XXX volts AC which could also be used as a speed control.

a_little_knoladge

Hi guys sorry for the delay in getting the new diagram done, this one should make more sense! let me know what you think.  

https://imgur.com/a/vxS5NcZ 

mcgivor I have considered a this but the higher DC voltage to AV 240 inverters are prohibitively expensive, cheapest 8kw one I found was £9k. I haven't settled on a motor yet but I have a few that I am weighing up. It is the motor controller that dictates the need for 250vdc however, and there are also a couple I am looking into but all would accept a range of about 110-500vdc. Yeah I have had a look into using a VFD (variable frequency drive) but they are usually manufactured to take 3 phase AC and chop that, could get it to work but requires tinkering and going straight onto the DC bus (if it has one) inside the driver, also they aren't as resilient to water and general crap as the automotive controllers I am looking at. 

Photowhit

Looks to me as if you have direct wire connection between the 48 volt Bus and the 250 volt Bus. I don't think that will work out well;

BB.

Let me see if I can do a simple diagram of just the "-48v" wiring of the "left" battery bank:

Batt terminal / -48V bus (one copper cable "daisy chained" from top to bottom, or every other battery pack)
- (0v) -48v cable
+- (24v)
+- (48v) -48v cable
+- (72v)
+- (96v) -48v cable
+- (120v)
+-(144v) -48v cable
+-(168v)
+-(192v) -48v cable
+-(216v)
+(240v)

Each above "step" (- to +) is one battery... And +- is those terminals attached together (in series).

If we take the first - terminal as 0volts, we see that first battery +- connection is 24 volts, the second +- connection is 46 volts, etc... 

And, you have tied a single copper wire (called -48vdc, but which is really "zero volt" reference) to every other series cell "down the chain".

You want +240 VAC at the bottom most cell, yet, the two cells up is "both" 0volt (first cell at top) and +192v down the string--You obviously cannot have both zero and +192 volts (and 144v, 96v, and 48v) on the same single copper wire run. So, there is your "first short circuit".

You have both series connected cells, and (effectively) parallel connected cells (battery packs) at the same time.

That is the same problem on the right hand battery bank too (shorting every 2 battery packs together).

And other issue... When you made your connections for the +48 volt daisy chain cable, you made the same electrical connections as the -48 volt chain. With the exception of including the + terminal of the bottom (last) battery packs.

Notice that your drawing picked (for example) the upper left "+" terminal, and following the copper (diagonal) series cable down to the lower right "-" terminal. The connection in this drawing is simply making a -48 connection on one end of a diagonal strap, and a +48 connection on the other side of the same copper strap/cable. So, other than the -48volt bus picking up the top/first battery pack, and the +48volt bus picking up the bottom "+" of the battery packs, they are exactly the same connections (-48v bus and +48v bus share 4 of the 5 same connections).

It is a very common idea that a person can series and parallel a set of cells (batteries/battery packs) at the same time and get both XX volt in series and YY volts in parallel at the same time. With simple copper wiring, there is no way of doing that.

You either have a series connected bank (240 VAC from two parallel banks), or effectively 10x 48 volt (2x 24 volt series packs) parallel connected into the "10" packs. EITHER/OR... Not both at the same time.

Take two 1.5 volt flashlight batteries, and connect them in series (3 volts) and parallel (1.5 volts)--It shorts the series connected cells out.

Regarding the use of VFDs... These are pretty commonly used in solar water pumping applications. Take a VFD that rectifies the (typically) ~240 VAC into ~340 VAC (into a high voltage capacitor bank), then that is the input into a variable frequency 3 phase inverter to drive a native 3 phase induction motor (or a 3 phase Permanent Magnet Motor--More efficient).

So, dump the one or three phase rectifier, and connect the solar array to the high voltage capacitors, and then through the VFI to the motor.

Here is a post about using VFDs and solar... Not a lot there, but it will give you an idea of what is happening in the field (solar powered 3 phase VFD controlled water pumping).

https://forum.solar-electric.com/discussion/comment/191136#Comment_191136

I am not very famiilar with the VFD/Water pumping field... But there should be enough to get you off in a working direction (aka your XXX volt battery bank driving the DC section of a VFD controller).

There are downsides with VFDs and standard 3 phase motors... VFDs (at least the "cheap ones"?) tend to be MSW (modified square wave) output... Driving MSW into an induction (or PM) motor gives you lots of harmonics, circulating currents, and other issues which can lead to shortened motor life (look for "inverter rated" motors, etc.).

-Bill

softdown

Forgive me for changing the subject. As a barge owner I have a question for you. I may need some type of large older boat to move my stuff across the north Pacific - including cars. My only experience is with smaller power boats and sail boats. Looking for recommendations if you care to share. I believe late summer offers the best weather window.