Battery Charging

System

First off...I am THRILLED to find this forum...it's the best that I've seen.

We're in Maine...off-grid...solar for about 1 and a half years. I have a question regarding battery charging...and WHO to believe.

Trojan says my bulk charge on my T105s should be 59.2...float 52.8...but THEN their literature says..."if using an inverter with a charger....follow THEIR charging info." My Xantrex 48v inverter has the rate LOWER on the bulk and HIGHER on the FLOAT....they also say....you guessed it...."follow battery manufactuer's charging instructions."

Aggghhhhh!!!

My question...how of a deal is the difference between 59.2 and 57.6 for BULK and
52.8 and 53.2 for FLOAT?

Confused? You should be living at MY house!

Thanks,
James

icarus

Re: Bettery Charging

Welcome to the forum. A couple of notes. First I would read and understand as much of the following as you can: http://www.batteryfaq.org/
http://www.windsun.com/Batteries/Battery_FAQ.htm#Lifespan%20of%20Batteries

Second, if you are living off grid I wouldn't (personally) worry about float voltage, since you will very seldom see it. As for the "real" answer, I would probably trust Trojan.

Others will chime in I'm sure,

Tony

BB.

Re: Bettery Charging

How is your water usage... If you are using a medium amount--you are probably charging enough. If near zero water usage, you are probably not charging enough. Too much water use, you are probably over/excessively charging.

If you are closing the place down for the winter (for example), then setting the charging voltages to the low end of the range will allow you to cut the water usage back so you don't boil them dry while you are gone.

Also, do you have a remote battery temperature senor. Many controllers tend to over estimate the bank temperature (self heating of the charge controller fools their internal temp sensor) and set the charging voltages lower than they should be.

-Bill

bryanl

Re: Bettery Charging

How to tell who to follow? Figure out where they are coming from. Go by your own measure, whose value you understand and can use properly, to guide what you do rather than following a recipe. For instance:

If you are using a medium amount--you are probably charging enough. If near zero water usage, you are probably not charging enough. To much water use, you are probably over/excessively charging.

This works because a good charge will cause a bit of electrolyte loss and the primary symptom of overcharging is excessive electrolyte loss. These two problems, overcharging and undercharging, are the major factors leading to reductions in battery life

hillbilly

Re: Battery Charging

As for the bulk rates, that's not really so big of a difference all in all. I know that for my Surrette batteries they have a suggested range of charging voltages depending a bit on the specific use and storage of those batteries. For instance higher discharges, colder temps, less capable charging capabilities (low PV to battery ratio for example), might all factor towards a slightly higher voltage setting, while the opposite would tend to lean more towards a lower bulk voltage. Watching the SG levels, and monitoring your water consumption are two good ways to narrow things down a bit better. You could use the above to consider where you might fall in that range, and/or pick a voltage setting somewhere in the middle and start monitoring your SG levels and water consumption. You might also ask your dealer, and or Trojan for further guidance on starting this process (and it is just that: a learning process that you will need to go through to get to know how your system works).
It tends to be a somewhat delicate balance between sufficient charging to completely recharge, versus cooking the heck out them and loosing excess electrolyte. We even typically change our voltage setting and absorb times a bit seasonally, as winter tends to be a bit tougher to charge the batteries back up, whereas summer tends to be easy to overcharge them.
Good luck.

westbranch

Re: Battery Charging

just to add a bit of additional info , if you haven't already, read this thread, post #13 for some additional pointers on chargers..
http://forum.solar-electric.com/showthread.php?t=5750

HTH
Eric

System2

Re: Battery Charging

Wow!

I KNEW I found the right forum. You all are awesome. Going by the most simple suggestions...(water consumption) I guess I'm doing alright. I use a moderate amount...I check them about once a month or a bit longer.

I also like the suggestion about CHANGING my rates seasonally...never thought of that...but coming in to another Maine winter...that's a very good idea.

I'm also CALLING Trojan first thing Monday and tryign to get a real answer. One "off-grid" neighbor doesn't think they give TRUE info....he thinks they give info that'll require you're buying MORE batteries sooner. If that were the case and my batteries were played out sooner than later...I wouldn't be buying Trojan again.

This IS a learning experience that's for sure.

Thanks again one and all...and I KNOW I'll be back with more questions.

James

BB.

Re: Battery Charging

On last suggestion is a Battery Monitor... Helps identify when batteries are being over discharged--and is very handy for others that may use the place and can be told to cut power usage if <75% on the meter, and start the genset if <50% and/or cloudy weather is ahead.

If the battery monitor saves you from killing one set of batteries through undercharging/over discharging--it probably pays for itself.

If you every convert over to AGM/Sealed batteries... A monitor will make your life much easier.

-Bill

niel

Re: Battery Charging

my bet would be trojan's numbers. i'm not sure what inverter you have, but if it has a provision for a bts, please be sure you have one and use it. this will compensate the batteries for temperature swings automatically.

halfcrazy

Re: Battery Charging

I have installed a bunch of Trojan batterys here in maine and they like the higher bulk voltage. I use 59.2 for a 48 volt system and my battery supplier also recomends this voltage. It really seems any lower and batterys die a short life here in maine

bryanl

Re: Battery Charging

charging won't "cook the heck" out of batteries if you use a proper 3 stage charger that reduces the charge voltage to float when the absorption current drops to an appropriate level and doesn't push the bulk charge voltage so high as to be dangerous to attached equipment.

The problem with many solar charge controllers for small systems is that they aren't that smart, which is why people fiddle with voltage settings and other worries when things go marginal.

As for battery monitors - they can be misleading as they are secondary measures of battery state. A properly made voltage or specific gravity measure properly interpreted is much more reliable. That is why good battery chargers work on how a battery responds to an applied voltage to determine what they do.

Charging is one thing, storage is another. If you have a lot of idle time for your batteries, consider getting a device that is oriented towards storage needs like the BatteryMinder(tm) or other device that will assure a top charge without overcharging and provide a sulfation inhibiting technique.

jeffkruse

Re: Battery Charging

I am on my second set of batteries (first ones replaced after only 3 months). I am now starting to believe that you can’t rely on the default settings for the charger. I also believe you can’t go by the voltage spec for the battery. You need to go by the SG.

I am now up to 59.5V (48V bank) for my Bulk and Absorb settings AND my absorb time is set to the maximum. I am now getting my SG up to the baseline (MK Deka FLA 1.275). I have 2KW of panels.

It’s been less than two weeks on this set of batteries so I have more playing around to do.
The battery monitor comes this week but I am afraid its going to tell me I am drawing 4KWH but putting 8KWH in just to maintain the SG at/close to full.

mike95490

Re: Battery Charging

jeffkruse wrote: »

The battery monitor comes this week but I am afraid its going to tell me I am drawing 4KWH but putting 8KWH in just to maintain the SG at/close to full.

Some batteries may improve after a dozen cycles, don't give up hope. With the voltages you are reporting, I'd look at the accuracy of the meters, and wires. May be a high resistance wire somewhere.

I wish there was a consumer grade/priced IR camera to look at things like this. Where's the hot spot?

hillbilly

Re: Battery Charging

I'm kind of with Jeff on this one, I just don't think that you can completely trust any other info than the SG readings. In theory, a good charger with temp compensation, set at the right voltage parameters *should* do a good job of correctly charging your batteries. A battery monitor is a huge help in being able to follow your discharge and recharging of your batteries... but all that said there are certainly some potential glitches in all of this, so above all else get a good Hydrometer (no floating balls or spinning dials) and use it to verify what your battery monitor and voltage levels are telling you.
Just a few little things that I've found to be at issue have been:
-Charge controller being "buggy" or quirky and switching into "float" too soon. In particular this seems to be an issue when using a generator to do the majority of the charging and then allow the PV to finish the job. I've been lucky to catch it a few times and reset it without issue, bottom line is to keep an eye on all parts of the system to verify they are working correctly.
-Temperature compensation not quite sufficient enough in really cold temps. This very well could be due to poor placement on my part, not really sure, but I've noticed that while it will cause the charge controller to up it's charging voltage it seems to take the batteries a while to "warm up" and therefore they don't always get quite enough juice if I don't run a longer absorb time.
-Trusting the battery monitor too much when it says that the batteries were "charged", this can be caused by the settings you choose but also recognize that the batteries may or may not be charged just going by the number of amp hours returned to the battery.
-Voltage readings can be tricky to understand as they can be affected by several factors. In particular a sulfated battery will read higher voltages due to increased resistance, also this will lower the charging current from the charge controller giving a very false impression of a charged battery.
All of the above is just to give you some potential pitfalls to watch for, and with a good hydrometer and battery monitor you can really learn a lot about how your batteries are performing. Good luck, keep us posted on how your system works out

icarus

Re: Battery Charging

Jeff,

Your 4 KWH out vs 8 KWH in may not be too far off, depending on how you are measuring it.

My rule of thumb is ~50% of name plate rating net/net out of the inverter.
So if you are drawing 1kwh out ac, you might have to produce ~2kwh just to stay in the same place.

Batteries are fundamentally inefficient to charge, taking a minimum of ~120% of ah to replace 100%, and as they near full they take more power proportionally. Couple this to charge controller and wiring losses and the numbers get even worse.


http://www.batteryfaq.org/
http://www.windsun.com/Batteries/Battery_FAQ.htm#Lifespan%20of%20Batteries

Tony

I hope I am not pointing out the obvious