WHEN COMMISSIONING BATTERY-POWERED SYSTEM, SHOULD BATTERIES BE FULLY-CHARGED, PARTIALLY OR EMPTY?

[Usman]

I am working on a pilot project for an inexpensive power system consisted of

2. x 48V 1KW wind turbine and a
   
130. w x 4 solar array for a small town in Africa to power street lights and a radio transmitter.
     
     

I wanted to know whether or not to fully-charge the Lead-Acid Batteries when installing the system.  

I would imagine there must be an industrial formula where the power from the hybrid source, the load, battery-size and other parameters are taken into consideration before choosing whether to install fully charged batteries, partially charged or completely discharged?

Any help would be appreciated.

Thanks.

[DamonHD]

I am no expert at all, but I think you'd never want the batteries to be fully discharged, even at install, to avoid damage.

A partial charge (sat >50%) on the batteries to keep them in good condition before the PV has a chance to charge them sounds fine to me.

Rgds

Damon

[la7qz]

Hi

First of all, your caps lock key seems to be stuck. Please don't SHOUT, not even in your headlines. It's annoying and puts people off reading your post.

i rEALLY hATE tHIS dAMNED cAPS lOCK kEY

Now to your batteries. If you have the opportunity to have them fully charged before commissioning the system, I would certainly take it. When I have had new batteries for my boat, I have always made sure the vendor has charged them before I install them. It is so much more convenient to charge the batteries in the shop with a good battery charger than on an anchored boat with no shore power.

I don't particularly relish the idea of sitting on the boat for a day running my engine to charge batteries, and I don't want to have to wait until the solar panels have brought them up to full charge before I can use power without having to worry about the state of my batteries. It can take a long time to bring a battery bank up from 50 to 100% with RE sources when you are consuming power at the same time. You will be in a similar situation where your only charging source will be your RE system, perhaps even with no way of using infernal combustions to charge them.

Completely discharging lead acid batteries WILL damage them. How much it will damage them will depend on the quality of the batteries and how long they are left discharged, but it will always cause some damage. In a situation such as yours where the end users may be less than technically proficient, I would strongly urge you to install some sort of circuit that will prevent the batteries from being discharged lower than 50%.

I spent a year in Cape Verde on my previous boat. I found that in those cases where cruisers had to leave the country with a local boatsitter looking after their yacht, they would invariably come back to terminally dead batteries. It was simply impossible to explain the basics of battery management to the locals. When I left my own boat in the hands of a local boatsitter for five weeks while I was delivering another yacht, I disabled everything except the led anchor light and two led reading lights. With 100W worth of PV panels, there was no way he could discharge my batteries even if he left the lights on all the time. I came back to fully charged batteries in good condition.

The boatsitter who looked after my boat had previously looked after the boat I delivered from Mindelo to the Azores. The batteries on that boat were terminal. I had tried several times to tell him that he must run the engine and charge up to 14.2 V as soon as the batteries were down to 12V. I found that he had occasionally run the engine to bring the batteries up to 12V and then stopped the engine...

If I was designing a RE system for a third world location, one of the most important things on my mind would be to make it as foolproof as possible. I'm not saying that Africans are any dumber than us. Some of the smartest people I know are Africans, but unlike us, they have not lived with technology since the day they were born and they have a lot of catching up to do. I know I would look pretty dumb alone in the jungle...

Regards, Owen

Yacht "Magic"

Anchored in the lagoon, French St. Martin

[spinningmagnets]

I agree that batteries should be fully charged as soon as possible, and kept at a full charge at all times. This will lead to the longest possible battery life, and best possible power service.

If you have access to some batteries that are partially or fully discharged, you should charge them up fully, and test them, before you spend money to buy them.

Even if a fully charged, but weak battery is free, if you put a weak battery in a pack with several new batteries, it will cause problems.

I wish you success in your efforts.  -Ron

[robl]

Perfect timing. I was wondering about this issue also.

I am on my third battery bank now. The previous sets lasted 14 and 11 years respectively. The current set is comprised of 8 Surrette S-530's configured for 48V. I'm quite happy with them so far, 4 months of off-grid use @ average load of 3.5KWH/day.

This is what Surrette recommends: (from http://www.surrette.com/pdf/BU-RS-614.pdf)

"If the battery bank is large in relation to the PV array (C/20 min) and loads are

large then the batteries will require a higher voltage setting. Also the battery

should be cycled deeply (i.e. to 50%) before starting an auxiliary charge source

such as a generator. Once every three months the bank should be discharged to

the low voltage set point before starting the generator. This is usually dependent

on the cut-off of the inverter which is usually 11 volts on a 12V system. The

batteries are designed to be cycled and a deeper discharge forces electrolyte

deeper into the active plate material and helps open up fresh reaction sites. With

large battery to PV systems, it is imperative that the battery bank is returned to

100% SOC once every 30 days. Full charge can be determined by charge

acceptance, which is ~2% of capacity at 100% SOC."

Aside from emergencies, I've never let my previous sets go down below 50% DOD. However, the Surrette suggestion kinda makes sense....

REgards

Rob