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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
Riplash likes this post
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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


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