Lead acid battery charging in cold weather

This blog covers lead acid battery charging at low temperatures. A later blog will deal with lithium batteries.

Charging lead acid batteries in cold (and indeed hot) weather needs special consideration, primarily due to the fact a higher charge voltage is required at low temperatures and a lower voltage at high temperatures.

Charging therefore needs to be ‘temperature compensated’ to improve battery care and this is required when the temperature of the battery is expected to be less than 10°C / 50°F or more than 30°C / 85°F. The centre point for temperature compensation is 25°C / 77°F.

Cold weather also reduces a battery’s capacity. This is another factor that needs to be taken into consideration, along with the load and charge rate compared to the battery capacity (Ah). Both of these factors affect the correct and consequent sizing of a battery for your particular application.

Battery capacity in Ah is usually quoted as a 20 hour capacity rating at 25°C. The discharge rate or load can be written as 0.05C where for example C is the load factor of the 20 hour rated battery capacity at 25°C.

Worked examples: If a 100Ah 20hr rated battery then a 0.05 load would be 100 x 0.05 = 5 Amps or 100/20 which is also a 5 Amp discharge rate over that 20 hour period. A 10A load on a 100Ah 20 hour rated battery would therefore be a 0.1C discharge rate, a 0.2C discharge rate on a 200Ah would be 40A and so on. C ratings also relate to charge rates as well as discharge rates.

When buying a battery you may see its Ah quoted at 20 (the standard rate), 10 and 5 hour rates so you can see how load ‘shrinks’ the Ah. Some even quote at 25 hour rates, which often fools people into thinking they are getting a bigger battery than standard.

To recap – capacity reduces at low temperatures, as it does for higher discharge C rates above the 0.05C 20 hour rate. This reduction in capacity due to higher discharge rates is due to Peukert’s Law.

Graph showing the effect on battery capacity due to temperature and load:

Lead acid battery differences

Lead acid batteries come in a variety of types:
  • Wet lead with the ability to top up each of the six cells with de-mineralised water.
  • The so called ‘sealed’ wet lead leisure or rather maintenance free battery. These cannot be topped up and often have a green go or red no go cell inspection indicator.
  • AGM (Absorbent Glass Mat) valve-regulated lead-acid (VRLA), where the electrolyte is absorbed in a glass mat.
  • Similar to the AGM, but the electrolyte is held in a Gel.

All of the above are however lead based (as opposed to lithium) technology. Besides lithium batteries Victron Energy sell VRLA AGM and Gel monoblocs (6 x 2V cells in series) due to their superiority over wet lead monobloc types. Victron’s range consists of:

  • Gel (Better cycle life than AGM).
  • AGM (Better than Gel for higher loads and well suited for use with inverters).
  • AGM Telecom. Designed primarily for Telecom applications, but also excellent ‘footprint space savers’ for marine and vehicle applications.
  • AGM Super Cycle (Best if frequent discharge to 60-80% DOD is expected).
  • Lead Carbon Battery (Improved partial state-of-charge performance, more cycles, and higher efficiency).

Additionally Victron also sell specialist lead acid type batteries.

  • OPzV 2V individual battery cells. Long life, high capacity gel.
  • OPzS 2V individual battery cells. Long life high capacity flooded tubular plate batteries for specialist solar applications.

Temperature compensation and charging

Now we know about the kind of batteries, capacities and loads we are dealing with, we need to put some numbers together for temperature compensation and charging.

The recommended temperature compensation for Victron VRLA batteries is – 4 mV / Cell (-24 mV /°C for a 12V battery).

Besides accounting for cold weather charging the charge current should preferably not exceed 0.2C (20A for a 100Ah battery) as the temperature of the battery would tend to increase by more than 10°C if the charge current exceeded 0.2C. Therefore temperature compensation is also required if the charge current exceeds 0.2C.

How to achieve temperature and voltage compensated charging

There are a range of Victron products to achieve this.

With our range of inverter/chargers and since VE.Bus firmware version 415 was released some time back this has ensured that:

– Temp compensation continues down to -20C

– This is for all voltage set-points, except for float, storage and the start of bulk charging

– As soon as the temperature goes below -30C, the compensation mechanism is disabled (normal charge voltages are applied) and a warning is shown.

For systems that don’t use an inverter/charger – we can use Smart Battery Sense to ensure that charging sources provide optimal voltage and temperature compensated charging to your batteries, by wirelessly transmitting accurate battery voltage and temperature values to your Solar Charge Controller or Smart battery charger.

This information is then used to set the ideal charging parameters, resulting in more complete, faster charging – improving battery health and therefore extending battery life.

The Victron Toolkit app allows you to calculate cable sizes and voltage drop. Here’s an example where cable length is the round trip of the positive and negative battery charging cables. This is so you get an idea of what Smart Battery Sense automatically takes into account to ensure the correct charge voltage goes into the battery, by ensuring the charge voltage is compensated for and corrected due to any cable losses.

Victron’s range of SmartSolar MPPT Charge Controllers all work with the Smart Battery Sense. In fact I’ve just fitted one to my motorhome, along with the required Smart Battery Sense, due to the fact the leisure battery temperature location when compared to the location of the controller can have a difference of up to ten degrees. Definitely a case for ensuring accurate temperature compensation.

Other products can be connected too by using what we call ‘VE.Smart Networking support’. See the VE.Smart Networking page.

Conclusion

With the above solutions I know I’ll be happier now that my batteries are getting exactly the right charge due to optimal temperature and voltage compensation.

Why not make sure you are doing the same…

John Rushworth


Punjo is not Puna : Not All Solar Panels Are Equal

Nii koi’s wife was pregnant with their third child, and as usual her food cravings seemed to change by the hour. This morning she wanted Pona yams with smoked fish light soup. Being a great husband Nii Koi dashes  to the nearby  grocery down the road  and ends up being sold Punjo yams ,a lower priced ,larger variety of yam. Most Ghanaians prefer the higher sugar content and finer texture in Pona yams even though they can be quite pricey especially when yams are not in season. Thinking he had found a great deal Nii Koi proceeded to complete his assignment.

His wife was very furious, I will not eat this yam

“All yam be yam he exclaimed” and she hissed back, Punjo is not Pona

To cut a long story short his wife refused to eat the Punjo yams and insisted that he get Pona yams to satisfy her cravings

Jinko Solar panels are durable and efficient

Selling Solar in a harsh economic climate like Ghana can be quite challenging ,it’s not unusual for prospective customers to ask questions such as  “why your solar panels cost Ghc X when so and so in the market is selling it for so much less at Ghc. Y.”

The simple answer is – Not All Solar Panels Are Equal.

Punjo is not Puna : Not All Solar Panels Are Equal

So when you compare prices for solar panels (and we do encourage you to shop around), you do need to pay attention to 2 key aspects of the panel’s quality – GRADE and MANUFACTURER TIER.

GRADE refers to the quality of solar cell used in the solar panel, and are categorized as A, B, C, or D. Grade A cells are the highest quality, in that they are tested against highest quality criteria to ensure there are no micro-cracks in the solar cell, and all the cells are of the same type. The quality diminishes for grade B, which may have micro cracks and not all cells are of the same type (they sometimes mix and match). Grades C and D are much worse quality with larger cracks and chips, and the cell mismatch is even worse.A typical solar cell will be exposed to sunlight throughout its lifetime. Sunlight contains harmful ultraviolet (UV) light that deteriorates all materials, including solar cells. The tiny flaws in the material become worse after prolonged exposure to sunlight, and its power output reduces over time.As a grade A cell has the least flaws to start with, its deterioration will be the slowest.

MANUFACTURER TIER refers to how automated a manufacturer is in its manufacturing process, its manufacturing volume, how long it has been in the industry, and how much it invests in R&D. There are 3 tiers to classify this:

certified engineers installing Jinko Panels in the heart of Ghana capital city,Accra

Tier 1 manufacturers are the top 2% of solar manufacturers, normally producing over 1 GW of solar panels in a year. They are vertically integrated meaning they make their own cells and wafers. They invest heavily in R&D, and have advanced robotic processes for manufacturing. They have been manufacturing panels for longer than 5 years. Tier 2 manufacturers are small to medium scale manufacturers, with little or no investment in R&D. They only use partial robotics in their manufacturing process, and rely more on manual work from human production lines. They have been producing panels for 2 to 5 years. Tier 3 manufacturers are actually just Assemblers – i.e. they assemble other manufacturer’s cells into a panel. This is 90% of the new solar PV companies, with no investment in R&D, and they use human production lines for manual soldering of solar cells instead of advanced robotics. They have been assembling panels for 1-2 years. You get best (and consistent) results from Grade A panels manufactured by a Tier 1 manufacturer. They may cost a little more on a per-watt basis, but when you consider the energy output and the longevity of their panels, you actually get more energy out of Tier 1 / Grade A panels than anyone else. And ultimately, you have to ask yourself what matters to you more — the total number of watts of a solar panel, or the actual kWh (units) of energy produced by the panel?

That’s why we at Nocheski Solar use Grade A solar panels from Tier 1 manufacturers like Jinko Solar, which ensures the best overall value in terms overall electricity output and long-term high quality.Hope this helps you when you compare solar panel prices.Let us know your feedback.All that being said, its  prudent to watch out for unscrupulous industry players  who may be selling counterfeited solar products but that is another whole discussion for another day.

Punjo is not Puna : Not All Solar Panels Are Equal

 

 

 


The hardware in Victron Energy Multiplus inverter/charger range has been improved: it can now switch much faster from inverter mode to mains mode. Combined with our high peak power ratings, this makes it possible to switch to mains mode before shutting down in an inverter overload alarm. This is especially useful in Self-consumption Hub-1 and 2 installations: it allows using an inverter/charger with a nameplate power below the system power. Multiplus inverter improved: faster switching to grid

The old hardware will take approximately 8.5 seconds to switch from inverter- to charger-mode, the new hardware can do it within half a second. Some notes:

  • single phase installations will be even faster than the half a second mentioned;
  • fast switching is only possible in the 3xx firmware versions. The difference between 3xx on one hand, and 1xx and 2xx on the other hand is approximately another 0.5 second in the worst case scenario: slightly differing frequency, and inverter being 180 degrees out of sync with the grid;
  • all larger models, 3kVA and upwards, already have fast-switching since a long time;
  • do not forget the other limit to using an ‘undersized’ Multiplus Compact in an installation: the AC transfer capacity. Max system load may never exceed the transfer switch capacity;
  • the load-shedding functions in the self-consumption hub-1 and 2 Assistants give options to further undersize a Multiplus Compact: use an external relay which is controlled via the Auxiliary output;
  • mentioned switching delays have not been measured exactly;
  • for parallel and three-phase operation, please check the Disqus comments below.

Lots of little details, but all together the conclusion is that this significantly reduces the chance of a Victron switching off in overload condition.Multiplus inverter improved: faster switching to grid

Availability

Despite stock and production logistics, all different models are shipping with the new hardware. Below table gives an overview of the current situation, from our main warehouse DSV in the Netherlands.