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Old 07-22-2017, 11:21 PM   #1
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Second Generation 4kW House Battery

I posted last year a Lithium Ion battery conversion from a Chevy Volt battery. The battery size was 2kW. This year I have developed a 4kW size for a marine application. In marine use there is more demand for higher voltage to support distributed electrical motor loads. To do this I setup the battery for 16VDC.
And the boat loads love the extra voltage (refrigerator compressor, anchor winch, and water pump).

The support for this battery will come from the new version of Victron smart charger, and a shift in the engine alternator charge voltage.

Images:
1) Battery utilizing the Chevy Volt cables for the sensing,

2) Battery wiring simplified way to strap the six batteries together,

3) Battery with BMS
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Old 07-22-2017, 11:48 PM   #2
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Interesting. Tell us more!

How much does this setup weigh? With all the volts that have been running around, I wonder how good the used sources for these from dismantelers.
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Old 07-23-2017, 06:31 PM   #3
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Well the advantage of this method is with a little labor, say 6-8 hours you can build yourself a powerful Li-ion battery for an affordable price.

I purchased a 16 kW battery delivered for $1,100 including sales tax. The lower than average price was due to some mechanical damage which was not part of the battery so it had no effect on what I needed.

It is possible to find a repair shop that will give them away, most larger auto salvage yards sell them for $1,500 where they remove the battery and if you are within their delivery truck run will bring the battery to your place.

The 16kW battery is mostly connections of 2kW packs, which weigh about 35 pounds. This one is twice that and the same footprint as an 8D.

The approach I am using is to re-strap the battery (the one pictured has 24 cells) I change the 24 cells in series to six four cell groups in parallel. This is not the only method. One could use the 24 cell battery pack as is or the 12 cell battery pack as is. You would then have very little work to do but would need to add a DC to DC converter or DC to AC, which are common methods used in solar collector so there is plenty of equipment out there to pick from.
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Old 07-23-2017, 08:23 PM   #4
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What are the specs for a single pack? And what are you doing for a bms?
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Old 07-24-2017, 05:41 PM   #5
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The 2kW battery is 12 cells at 48VDC. Re-strapped in the 3S configuration they yield 11-12.5 VDC range.

The BMS is from China (BesTech Power) and represented by Electric Car Parts Company, in Utah. I use a 100 Amp BMS, which is twice my trailer's needs, my highest load is the tongue jack which has a 30 amp fuse. I tell them the cell voltage so that they get the BMS programmed correctly. Eventually I will be able to purchase a BMS and set the programming myself, much like what can be done with Victron equipment.

If you go with the inverter idea the 48 VDC battery would fit perfectly with a Victron Phoenix Inverter which have around 95% efficiency. The Chevy volt battery has a 10% guard band on power so it is really 10% larger than specified.

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Old 07-26-2017, 09:27 AM   #6
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To continue with the Victron system solution I would. Setup 48VDC battery bank, purchase a Victron 48VDC charger/inverter and run most of my loads if not all off the inverter.

Shore power and/or Solar could charge the batteries and continue to operate as the power source too.

Advantages: many more equipment/appliances to choose from. The power would support AC with no problem, sizing could be changed overtime, low cost of batteries (typical price $1,500 for 16kw).

Disadvantages: Space needed, upgrade cost of charger/inverter, ....
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Old 07-26-2017, 09:39 AM   #7
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Hi

I suspect you mean 4 KWH rather than 4 KW. 40V at 100A for 0.0001 seconds is still 4 KW.

Bob
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Old 07-27-2017, 11:37 AM   #8
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All true thanks, yep we are talking energy.

I guess you didn't have anything else to contribute to the concept?
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Old 07-27-2017, 01:07 PM   #9
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Hi

I'd retain the series connection of the cells. That's a left turn right at the start where you made a right turn. It gets off into an entirely different set of things. Both approaches have their issues. It's not in any way clear that either one is "perfect".

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Old 07-27-2017, 02:53 PM   #10
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Yes I like the 48 VDC idea. The re-strapping is tricky and can cause problems if done poorly. You are correct, there is no perfect answer. The 48 VDC battery is below the 50 VDC safety threshold which would reduce the effort to use that amplitude of voltage. The higher voltage uses a smaller size copper wire. It might even be possible to use the Chevy Volt BMS but I bet you would really need a bunch of internal design information to set that up.

Here is an example of issues that would need to be address: how would 12VDC be provided? (would using the factory power supply make sense?)

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Old 07-27-2017, 03:35 PM   #11
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Originally Posted by sgschwend View Post
Yes I like the 48 VDC idea. The re-strapping is tricky and can cause problems if done poorly. You are correct, there is no perfect answer. The 48 VDC battery is below the 50 VDC safety threshold which would reduce the effort to use that amplitude of voltage. The higher voltage uses a smaller size copper wire. It might even be possible to use the Chevy Volt BMS but I bet you would really need a bunch of internal design information to set that up.

Here is an example of issues that would need to be address: how would 12VDC be provided? (would using the factory power supply make sense?)

Steve
Hi

48V makes things pretty easy. It's the good old telecom standard voltage. There is a *ton* of surplus out there designed for a 48V battery system. Fuses, switches, connectors, relays, are all out there. Most of them were designed for very long usage life. You can even find 48V LED lighting.

Coming up with packaged switching supplies to turn 48V into anything you would ever need is dirt cheap and very efficient. You can do 12V point of use regulation if you wish. Same is true of 5V for things like USB. Enable / disable inputs and low drain when disabled are not uncommon features.

Charging at 48V is also do-able, but not quite as telecom centric. There is enough solar going in at 48V to make things like controllers fairly easy to find. They aren't plentiful, but you can find them.

To me the BMS / equalization / monitoring issues are what really make the series connection the way to go. The cells were matched originally (I assume ...) so keep them running that way. Detecting and isolating a single cell issue is *much* easier with a straight series connection. You never *want* to have a cell fault. You very much want to promptly detect and respond to it if it happens.

All that said, do you *trust* the electronics? Your trailer breakaway switch needs a +12V source. Do you go with the 48V and a switcher or put in a (small) 12V battery for that and a few other minor items (propane detector ...) ? No perfect solutions ....

Bob
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Old 07-28-2017, 11:03 PM   #12
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Good stuff:
Another point is that most of the 12volt wiring would be used in the 48 volt system. Using 48 volts would reduce the line loss.

I took the battery down to the boat today, two boaters saw the battery and wanted to know all about it. One fella wanted to use them for a home backup power system instead of a backup generator. The other agreed that the higher voltage would fix his anchor winch soft performance, he was considering switching to a hydraulic winch.

I have added a way to adjust the engine alternator charge voltage. I can manually vary the value to allow the charging of either a lead acid battery or the 16 volt Li battery.
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Old 07-29-2017, 09:09 AM   #13
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Hi

Lithium batteries are a bit picky about how you charge them. Lead acid batteries are fairly tolerant of this and that by comparison. Since you need "electronics" to do the lithium charge stuff, running a DC/DC converter to get whatever voltage you need isn't a major increase in complexity. It also isolates you a bit better from interesting issues on a vehicle electric system.

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Old 07-30-2017, 10:24 AM   #14
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Good point, I hadn't thought of Lion being picky but it is a good way to impress on others the additional requirements to use Lion batteries.

I like the safety features in having those electronics. It is impressive whey you short the system output the system shuts down without any great massive arc.

The second largest cause to automobile fires is electrical short circuits. I setup the BMS (battery management system) to pass up to 100 amp continuously before the BMS will switch off, that might still be a problem for the case that it isn't a dead short but the RV load has protection for this.
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Old 07-30-2017, 01:07 PM   #15
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Hi

One of the most basic things you need is a "dead cell" detector going into the charger. With a low voltage stack, taking one cell to zero puts the others into "nuke" range if the charger keeps running. With parallel connections of cells keeping things sub melt down gets a bit involved, even without the charger.

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Old 08-01-2017, 09:52 PM   #16
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Dead cell detector, is mostly cover by the BMS controlling battery balancing.

I the 48VDC version the BMS monitors each cell with no other cells in parallel. In the 12 volt version most of those are 4 batteries in series tied together, or in the 24 cell battery that would be 6 cells at each voltage.

The 2 kWH first generation battery was 12 cells, a 3S configuration for four cell in parallel.

I haven't experienced a dead cell yet, I think the much lower current draw used by house batteries minimizes this possibility.
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Old 08-02-2017, 09:28 AM   #17
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Hi

An open cell is a pain, but not a hazard. A shorted cell is a hazard. With parallel cells you have no real idea which cell is getting what. Most BMS systems level up once a full charge is done. Yes that is a bit weird.

Bob
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