Battery Dilemma

[dscheckman]

Hello All, I have a small hydro system that provides an alternative and backup to the grid power I also have. During its peak ( about 7-8 months a year) it provides about 325 watts continuously. It bottoms out at about 50 watts if and when it gets dry in the summer. It's a 48 volt system which helps to deal with long wire runs. I use a 6 circuit transfer switch and switch circuits back and forth from the hydro inverter to the grid depending on the hydro output. This system has worked well for over three years.  

Okay now the problem. The batteries, 4x12 volt 165 amp hr Power Battery Solar gel cells (controlled by a tri-star 45) seem to be biting the dust. They go up to voltage but even a small load causes a large voltage drop and eventually the low voltage disconnect on the inverter kicks in and the inverter shuts down. Of course when the load then goes away the voltage goes back up and the inverter comes back on and so forth. I have to watch the battery meter like a hawk and try to keep the load balanced with the hydro output.So I think I need new batteries. The dilemma is this. I now believe the batteries failed somewhat prematurely because of the low amperage at which they recharge. (max 6.5amp@48 volts min 1amp@48 volts)I never let them go below 80% SOC and bring up to full charge daily. I hate to get a smaller bank as this size or even larger provides a pretty good backup as well as a buffer to the way our use cycles daily. I can envision adding some solar or enhancing the efficiency of the hydro but right now I can't justify spending the bucks on this hobby project. I'd like to stick to sealed batteries as they are in a fairly airtight space that would be awkward to ventilate. I do have the ability to charge at a higher rate (35 amps)with the inverter on grid power but that seems a little backwards. So any advice out there? What batteries? What size batteries. Oh, and not much is available locally. The Power batteries I have were the only ones I could find previously at a reasonable price. The basic question , What are the best sealed batteries for recharging at low amperage?

Thanks for any help ,

David in Vermont

[SparWeb]

Have to do a bit of math to get a handle on this one.  I don't know how this is going to go either.

Batteries:  12v x 4 @ 165 Ah.

C/20 charge would be 165/20 = 8.3 Amps

Your charge current = between 1 and 6 amps.

Your charge rate is somewhere between C/100 and C/30.

That's a pretty small trickle compared to the "optimal".  This isn't going to be the kiss of death though, unless....

Have you ever equalized them?  It doesn't sound like it.  Try reading up about the benefits of equalizing the batteries every month.  If you have NEVER done it then they may be unsalvageable.  

[Flux]

I don't know what life you can expect from gel cells under these conditions.

Gel are worse than VRLA for getting charged, the final 20% takes a very long time. If you are using them regularly as you seem to be doing then they are probably never fully charged and having a higher charging current available may not help much as the final part of the charge will be at low current even if you can speed up the bulk.

I am not sure how much you can raise the voltage for cyclic use, VRLA will let you raise it quite a bit above the normal float value. You can't equalise them in the same way as flooded cells but I think you can do it a bit for a short time.

I think VRLA would be better if you must have sealed batteries but I would think you would do far better with flooded ones. With flooded ones you may have to use calcium technology with a low charge rate to get them up to volts but that should never be an issue with gel. I don't think the low current in its own right is the problem as long as you have been able to get them up regularly and you say you can do this daily.

I would look at the individual units with a voltmeter and see if they are all the same or whether you have a duff cell in one unit that is messing up the whole string. If they are all equal then they are probably worn out.

Batteries are a pain and obviously you mainly need them for back up, if you cycle them all the time they won't last nearly as long as under float and standby conditions.

I would have hoped they would have done longer but I am not familiar with them, many of the solar sealed ones do have a good life but you don't half pay for it in the first place. If these were budget ones they may have run their course.

Flux

[tanner0441]

Hi

Have you checked all the connections if the voltage drops instantly the load goes on? Also as there are more than one battery have you split them and tested them individualy, I cant see all the batteries going down at the same rate. I had to test my batteries and I used both fillaments of a headlight bulb as a load 100W (ish) across my meter, and monitored the rate the battery drops.  As the other post says have you equalised them, i.e. put them on a charger and brought the voltage up to about 14.5 for a few hours?

Be careful with Gell batteries and keep your eye on the case temperature. Google Gell batteries and look at the maintainance recomendations. I don't know your inverter but if it charges as well you may be able to program it for different battery types...

Brian.

[richhagen]

Steven, he has sealed batteries, so depending upon the manufacturer, equalizing may not be recommended, or may be at a reduced hold voltage.  

For the poster, most sealed batteries contain a catalyst to aid in recombining any hydrogen and oxygen that collects in the sealed cell.  Significantly overcharging can cause a pressure buildup which can cause the sealed vents or valves depending upon the design to open up, in some cases reducing the life of the battery as the water vapor and components can escape. Rich

[Roob]

I was wondering if the grid can be your battery. I guess I am bringing up other conciderations like if your utility allows that and if your inverter is up to the task.  By selling all power to the utility the hydro plant would be "working" for you at all times not putting power into a battery bank that may or may not cough it back up again when needed.  I apologize if I have made assumptions, I am new at this blog thing.