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[Project] "capacity enhancer" for mobile home
#1
Hi to all, into my ongoing project of building a small powerwall battery bank something else has come in between.

I have bought a medium (european style) mobile home. Is quite fully, but more or less standard equipped. The interesting infos regarding my coming question for the community are:

- solar panels 200 W
- 2 batterys 12 V 90 Ah AGM, one for the car, one for the home
- both are loaded by line , both are loaded by driving/Motor, both are loaded by solar (as usual)


- during "housing" only the home battery is used, the car battery stays undischarged (as usual)
- Sat TV, frigo, light, small inverter at 12 V (600 W) for occasional use,
- plus heating which uses about 50 Watts for the vents if in use.

We would like to be able to get through for a few days without line.
For all favourable situations the home battery might just be sufficient, but if we need heating, if its raining (no sun) for a few days the fun might come to an end very quickly.
It is clear that any sized bigger battery might come to an end sometimes as well, but i want to have at least a bit more capacity as the above mentioned 12 V 90 Ah. (the backup is line current or the motor or a generator).


The options are:
- another 12V 90 Ah AGM battery, there is a place for it (250 $)
- another 12 V 90 AH LiFePo, might fit into the place, (1000 $)
- something else.

I do not like the AGM, these are sensible leads, can only be used 50 % capacity or degrade quick, and it is very heavy.
I do not like the LiFePo, because it either has to live with the voltage levels allowed for the AGM (when in parallel), and for the price.
(and LiIon cannot be directly used, because the Voltage leves are wrong for 3s and 4s to be paralleled to Lead)

But i have 5 kWh in Liion around here already. In 10sxp Blocks, with 36 Volts.

In searching for a concept to implement that i have to take in account the 12 V level of the car, the already complex situation of energy supply ( 3 sources for energy), the complex management of the batterys (load both, protect the car bat), and so on.

I thought through many possible configurations, using the higher Voltage for inverters, adding charger from solar and line for the 36 V, and so on.

In the end, it helped to define my problem to be solved,  i nailed it down to
- i need additional capacity
- i do not need high(er) wattage. (the inverter is sufficient and can stay at 12 volt)
- Basically the car has no "structural" problem of the environment, its just missing home batt capacity.

So i came to the strange concept of just a "capacity enhancer", which will be connected in parallel to the home battery, and nothing else.

[concept]
The enhancer supervises the home battery and does one of the following three things (as long as its own capacity lasts):
- on 12.8 Volt of the home batt it does nothing 
- below 12.7 V of the home batt the enhancer starts to supply increasing current to the home batt with a linear correlation to lower voltages. In effect t takes the load which "obviously" drops the batts voltage, limited to 10 Amps.
- over 12.9 enhancer start to surge energy from the home batt (as well limited to 10 Amps), as well with a somehow linear correlation, because the battery is "obviously" fed.
- If the enhancer is empty, the AGM has to supply the load alone, and will be discharged then - as last in the row.
- If the enhancer is full, the charger can fully load or "occasional balance" the AGM as usual.

So, in "Normal use", the AGM stays mostly full (which it likes), the capacity is taken to and from the enhancer, cycling it. That increases lifetime of the AGM.
Shorttime high loads (inverter) need help from the AGM over 10 Amps, discharging it, but it will not be much.

In summary, i need just the Enhancer batt and a bidirectinal inverter, controlled to above rules. I have no complex connection to the mobiles circuitry, the circuitry or its parameters must not even be changed. There ar some losses of energy, because it goes through the enhance inverters twice.  But, i do not have limited resources of energy, i have limited resources of STORED energy, so no problem there).

It looks like i can get 2-3 kWh plus two standard Alipress inverters with an Arduino in a PC case, and have 3-5 times the energy of an AGM for half the weight.

My questions so far are:
- any comments on the concept ?
- are there circuits or supplies, which can just be used for the inverters functionality i need, or is that an issue to be build by myself?

(Just to mention, i can build that, but in general i would not if i can buy things. )
(Just to mention, if a current sensor/Feed through can measure the current of the Home battery, the regulation/control can be made even more easily and more sophistically. A feed through current transformer is imho no change of the cars circuit).
1 kWp in Test
4 kWh battery target - plus Mobile Home battery
Ultra low cost
Electronics ? No clue. Am machinery engineer.
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#2
Is it electrically heated ?
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#3
(04-07-2019, 08:53 AM)Sean Wrote: Is it electrically heated ?

No. Heating is propane, only vents for distributing the heated air and for controlling purposes necessary.
1 kWp in Test
4 kWh battery target - plus Mobile Home battery
Ultra low cost
Electronics ? No clue. Am machinery engineer.
Reply
#4
(04-07-2019, 08:38 AM)Cherry67 Wrote: For all favourable situations the home battery might just be sufficient, but if we need heating, if its raining (no sun) for a few days the fun might come to an end very quickly.

If you are heating on gas why is the battery being impacted ?
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#5
(04-07-2019, 09:26 AM)Sean Wrote:
(04-07-2019, 08:38 AM)Cherry67 Wrote: For all favourable situations the home battery might just be sufficient, but if we need heating, if its raining (no sun) for a few days the fun might come to an end very quickly.

If you are heating on gas why is the battery being impacted ?

50 Wh per hour heating, 2 Hours TV 150 Wh, Laptop, a bit lighting. Make half of the usable 600 Wh of the AGM niche in one day.
1 kWp in Test
4 kWh battery target - plus Mobile Home battery
Ultra low cost
Electronics ? No clue. Am machinery engineer.
Reply
#6
Here is some of what You might use:

36 volts to 12 volts 20A: ZXY6020S NC DC-DC Power Supply Module Programmable 60V 20A 1200W (Banggood)

12 volts to 36 volts 10A: 1500W 30A DC-DC Boost Converter 10-60V to 12-90V Step Up Power Supply Module (EBay)

Warning, do not use at the same time, they do not like each other, the booster just quits. Lucky, just a blown fuse, not so lucky ,unit is to be binned.

However using an arduino to control 2 relays that energizes these gadgets, one at a time, will work nicely.

I have used this setup for 2 Years: 48 Volts Lead-acid and 24 Volts LiIon. Whenever one system needs a boost I can transfer 500 Watts in either direction.

ChrisD
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#7
(04-07-2019, 11:46 AM)ChrisD5710 Wrote: Here is some of what You might use:

36 volts to 12 volts 20A: ZXY6020S NC DC-DC Power Supply Module Programmable 60V 20A 1200W (Banggood)

12 volts to 36 volts 10A: 1500W 30A DC-DC Boost Converter 10-60V to 12-90V Step Up Power Supply Module (EBay)

Warning, do not use at the same time, they do not like each other, the booster just quits. Lucky, just a blown fuse, not so lucky ,unit is to be binned.

However using an arduino to control 2 relays that energizes these gadgets, one at a time, will work nicely.

I have used this setup for 2 Years: 48 Volts Lead-acid and 24 Volts LiIon. Whenever one system needs a boost I can transfer 500 Watts in either direction.

ChrisD


Usage of 2 converters separately for either direction is obvious, i have the some types of lower currents here in my stock.
Interesting, i found on the higher currents you pointed out ones which have an in built low-Voltage shut-off, which is exactly half of the task to get them going according to my concept.  (Would work for the boost converter part).

For any switching i will use Mosfets, not so much clicking... Big Grin 

Thanks for your input.
1 kWp in Test
4 kWh battery target - plus Mobile Home battery
Ultra low cost
Electronics ? No clue. Am machinery engineer.
Reply
#8
(04-07-2019, 11:46 AM)ChrisD5710 Wrote: Here is some of what You might use:

36 volts to 12 volts 20A: ZXY6020S NC DC-DC Power Supply Module Programmable 60V 20A 1200W (Banggood)

12 volts to 36 volts 10A: 1500W 30A DC-DC Boost Converter 10-60V to 12-90V Step Up Power Supply Module (EBay)

Warning, do not use at the same time, they do not like each other, the booster just quits. Lucky, just a blown fuse, not so lucky ,unit is to be binned.

However using an arduino to control 2 relays that energizes these gadgets, one at a time, will work nicely.

I have used this setup for 2 Years: 48 Volts Lead-acid and 24 Volts LiIon. Whenever one system needs a boost I can transfer 500 Watts in either direction.

ChrisD
In checking what i have as converters in stock i found what possibly might be the problem (see bold marked):
When the converters have CC adjustment (as Current limiter) then the current measurement resistor might be in the ground connection of the converter in question. But as you are connecting all grounds together (hardly possible to do different) you have shortcut it and the limiting doesn't work anymore.... Sad ....
1 kWp in Test
4 kWh battery target - plus Mobile Home battery
Ultra low cost
Electronics ? No clue. Am machinery engineer.
Reply
#9
Strange things happen sometimes....  when i wrote the above, it was just a concept i wanted to have, but didnt know how to do it.

Then i found a working solution which is in general described in https://secondlifestorage.com/showthread.php?tid=7330
Sorry i'd better put some of the stuff there in this thread.

But, obviously when i am going to describe details of the bidirectional converter i will do it here, for obvious reasons fo discussing.

For the ones which have found this only now, i will outline the technical background what i am doing, in some statements to avoid unnecessary questions:

- I describe a solution for connecting a 12 V ( lower voltage) LA (Lead Acid) battery with a 36 V ( higher voltage )  LiIon (any Chemistry) Battery
- Power transfer works in both directions, in that way that the LA battery is held clos to fully loaded ( which is good), and the Higher Voltage batt "helps" in feeding the 12 V Loads.
-  Usage of this is advised in Mobile homes, where you might need some/much more energy than the typical Mobile battery can supply. Usage in Grid tie isses might not be so obvious.
- Power level is quite limited, compared to the high capacity of the 36 V battery, because there is not much more needed.
- The LA Battery is the Working battery, The Higher Voltage batt is some sort of Buffer
- the main idea, having two dc supplies connected is not so much my idea, but the Car industry is haggling with this idea already for quite awhile. the 12 V of any standard ca is not so much a level where todays high energy car installation would like to work on. But the constructors are stuck on an existing technology, where a change may be technically advateous, but is not advised on non-technical reasons.
- This may have quite a lot of variations, which are only obvious once you have understood the pretty behavoiurs of the system i describe.

So, enough of the introduction.

------------------

Simple bidirectional converter, Building Plan

It needes just two converters, a buck and a boost. Both are available from eBay and Ali. No additional Control of circuitry...

The Boost is the typical type advertised as "1200 W Boost........."

The Buck is the typical type advertised as "300 W Buck....."

 

Here you see both of them mounted in a standard PC case. This was for easy build during first development.
If somebody still has doubts which ones to buy, i will supply actual links. But, as you know, links might die quite soon of this stuff.

The two converters are connected with this circuit plan:


Yes, no additional circuitry.
Yes, both converters "should" transfer energy in a circle. But they wont.
Yes, both converters have current shunts in the ground connection, and they are connected in parallel. Doesnt matter..... (as long as the ground wires are acceptable diameter and connected electrically stable)

The preparation of the converters goes as follows:

The Buck needs a bridge on the underside: (switching the syncronous mode off)
The resistor R7 gets a short. You must not remove it, just give it a short. That sounds easy, but might not be.... ist VERY smal there.
(the picture shows a removed resistor, its still stuck besides...  Use a magnifier... Big Grin the wire is 0.2 mm....



The Boost needs a bridge on the top side: Just connect the pads marked. This shorts a reverse polarity protecion which is provided in the converter ( not documented anywhere) but neither needed nor helpful. The wire must be able to carry the input current of the converter. So give it some size, but dont overdo..



Now the converters get preadjusted.

For setting into operation, just give them apropriate Input and Output conditions.

- Adjust Buck to 12.8 V Output, CC to 1 A ( CC will be changed later)

- Adjust Boost to 39.5 V, CC to 1 A Input, Undervoltage protection to 13.2 V.  ( CC will be changed later)
The value of 39.5 V is my choice not to stress the Li Ion Cells with the 4.2 V/cell in summer. You might choose this voltage to your choice for the top voltage of the LI Side.

Now the "complicated" wiring  begins.
- connect the ground terminals of the convertres anti-parallel,  means input to output. Use sufficient wire soize for the currents. cCare for good tightening of the screws.
- connect + Side of Boost input to Buck output as the 12 V side.
- connect + side of the Buck input to the boost output as the 36 V side.

Now the  bidirectional converter should work. Only the current limiting is not properly adjusted.

Start a checking and Connect a lead acid battery and any 36 V LiIon.
The LA should be full and settled to 12,8 V.

If you start to surge the LA, the Buck should start to deliver current. If you get appropriate conditions you can adjust the CC to your liking. a 7 Amps should be in the range of 12.6 V, otherwise look for the thicknes and Ri of your test wiring.

If you start to charge the LA, then nothing happens for the rising from 12.8 to 13.2 V, then above that voltage the converter should start delivering power to the 36 V LIon side. Again care for apropriate conditions for adjusting your Boost CC. You might need 13.8 V for about 8-10 Amps on the 12 V side. That does a little depend on very Low Ri on the 12 V side, you must consider the Boost does REALLY load the wires for geting Power, and any voltage loss adds to the UVP voltage setting.

One thing is to mention - the converters have losses, check on supplying fans and fan control to your finding.
Thats for now, if i forgot anyting pls. start to comment.
1 kWp in Test
4 kWh battery target - plus Mobile Home battery
Ultra low cost
Electronics ? No clue. Am machinery engineer.
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