131 daily cycles completed on my lithium battery bank. No drama, no problem. Not very interesting subject matter for a blog.
After tinkering with various settings of charging that only seemed to provoke one cell to want to wander off towards "higher ground", I reverted back to the original scheme of charging to 3.50V per cell (28.0V for the pack) but only for 30 minutes instead of up to 60 minutes. All charging for longer seemed to achieve was to make one cell go high and cause the rest of the pack to drop (as the charger wound back the power).
Charging to the original Voltage and keeping the time short seems to be the best way. It also has the side benefit that the water heater comes on sooner.
I'm now going into business making these things!
I'm working with a friend who runs Sustainables4U and we're packaging these storage systems for stationary (not moving from the coal shed) and mobile (on a trailer or in the back of a van) applications.
We've taken delivery of a batch of 200Ah Winston cells and will make a prototype portable generator. Something you can use at a building site or at a festival or even an eco show in a field that will make mains electricity to use without the noise, smoke and smell of a petrol generator - the sort that are always burbling behind burger vans at car boot sales...
We'll have a sort of flight case on wheels that will hold either 4x 200Ah cells or 4x 400Ah cells to give 2kWh or 4kWh of usable energy storage and a 1kW or 3kW pure sine inverter respectively.
I've even invested in some PCB CAD software to turn out a proper version of the inverter interface board so it won't even be bodged together with stripboard and bits of old string.
Friday, June 29, 2012
Saturday, May 19, 2012
More Charging Experiments
Not much to report for a few weeks... Thankfully.
The Winston battery pack continues to do nothing other than sit there and do it's job without fuss, chemical smells, or sudden death.
April's final generation figures were interesting in that they were the same as March's figures. That's interesting because March was one of the sunniest on record and April was one of the rainiest on record.
May is turning out to be a mixed bag and a bit disappointing. We had a long run of gloomy days and the main lithium bank hit the bottom a few times. On one run of bad weather I also depleted both of the backup Ritar lead acid batteries as well, using an old 1kW inverter to run a pair of the lab power supplies to charge the lithium bank during the night.
The lithium battery protection works well, sounding the police car siren at low battery and then shutting down the inverter when the weakest cell gets to 2.999V.
Then during the day after using the Ritar battery, I turn the lab power supplies the other way round and use the solar to recharge the fragile lead acid batteries first. It doesn't matter if the lithium bank sits at the bottom for a few days without being charged much but the lead acid ones need charging as soon as possible.
I might set up a more permanent hybrid battery system to make use of the lead acid batteries as a "battery of last resort". Used that way they might last for many years, if only discharged once in a few weeks, rather than every day.
I've also been playing with the lithium bank charge settings. Cell no. 8 has taken to reaching full charge a bit before the others. This is a feature of the bank being bottom balanced and the longer absorption charge times I've been playing with (now up to 50 minutes). At 28.0V absorption level, the cell was getting up to 3.58V before charge end, while the others were getting up to 3.51V. But cell no.8 rockets up to this high in a few minutes at the end of the 50 minutes, causing the other cells to actually fall a bit. So I've been winding the absorption Voltage down, a bit at a time, to see at what point the cells will remain close together.
At 27.7V, or 3.462V per cell, this seems to be the case. Today the pack sat at absorption for the full 50 minutes and all the cells remained fairly close together in Voltage.
The Winston battery pack continues to do nothing other than sit there and do it's job without fuss, chemical smells, or sudden death.
April's final generation figures were interesting in that they were the same as March's figures. That's interesting because March was one of the sunniest on record and April was one of the rainiest on record.
May is turning out to be a mixed bag and a bit disappointing. We had a long run of gloomy days and the main lithium bank hit the bottom a few times. On one run of bad weather I also depleted both of the backup Ritar lead acid batteries as well, using an old 1kW inverter to run a pair of the lab power supplies to charge the lithium bank during the night.
The lithium battery protection works well, sounding the police car siren at low battery and then shutting down the inverter when the weakest cell gets to 2.999V.
Then during the day after using the Ritar battery, I turn the lab power supplies the other way round and use the solar to recharge the fragile lead acid batteries first. It doesn't matter if the lithium bank sits at the bottom for a few days without being charged much but the lead acid ones need charging as soon as possible.
I might set up a more permanent hybrid battery system to make use of the lead acid batteries as a "battery of last resort". Used that way they might last for many years, if only discharged once in a few weeks, rather than every day.
I've also been playing with the lithium bank charge settings. Cell no. 8 has taken to reaching full charge a bit before the others. This is a feature of the bank being bottom balanced and the longer absorption charge times I've been playing with (now up to 50 minutes). At 28.0V absorption level, the cell was getting up to 3.58V before charge end, while the others were getting up to 3.51V. But cell no.8 rockets up to this high in a few minutes at the end of the 50 minutes, causing the other cells to actually fall a bit. So I've been winding the absorption Voltage down, a bit at a time, to see at what point the cells will remain close together.
At 27.7V, or 3.462V per cell, this seems to be the case. Today the pack sat at absorption for the full 50 minutes and all the cells remained fairly close together in Voltage.
Sunday, April 8, 2012
New Production Record!
March 2012 was the best month ever for energy production and utilisation on my solar system.
Solar AC energy used (measured through the inverter output OFGEM approved meter) was 183kWh for the month, beating even last year's record of 177kWh in May! That just goes to show how phenomenally sunny it was this March.
And this total, compared to the grid energy consumed for the whole month of March of just 46kWh, means that 79.9% of all my electricity use was provided by solar power.
The weather wasn't the only factor though in this surge of utilisation. The lithium battery bank is making a big contribution. I don't have to worry about running the pack down on dull days and leaving it partially charged for any length of time, so I'm more likely to use it.
We've had free hot water on several days when the battery finished fast charging by about 11.30am and then the rest of the day was spent diverting between three and four kWh of energy to the water heater.
With the good weather, the pack has generally only been discharged by 20% per day and has only hit the "bottom" once since installing it in February.
Solar AC energy used (measured through the inverter output OFGEM approved meter) was 183kWh for the month, beating even last year's record of 177kWh in May! That just goes to show how phenomenally sunny it was this March.
And this total, compared to the grid energy consumed for the whole month of March of just 46kWh, means that 79.9% of all my electricity use was provided by solar power.
The weather wasn't the only factor though in this surge of utilisation. The lithium battery bank is making a big contribution. I don't have to worry about running the pack down on dull days and leaving it partially charged for any length of time, so I'm more likely to use it.
We've had free hot water on several days when the battery finished fast charging by about 11.30am and then the rest of the day was spent diverting between three and four kWh of energy to the water heater.
With the good weather, the pack has generally only been discharged by 20% per day and has only hit the "bottom" once since installing it in February.
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