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MI drew
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# Posted: 4 Jan 2014 07:36
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I picked up 2 Duracell 6v golf cart batteries rated at 105 minutes at 75amps. I'm only running a 1500 watt PowerBright inverter, some CL bulbs, a 9" tv/dvd, and small fan on my wall heater. I do not have solar panels yet. I am charging them off my generator and charger that can do 6v at 15amps, 12v at 2 and 15amps, and 100 cranking amps.
Here's my question. Will the batteries charge and discharge at the same rate? This AM the one battery was at 5.9 and the other at 4.6 so my inverter alarm was going off for 10.5. Should I charge them independently on 6v or wired together at 12v? I did it on 6v yesterday to get me at 6.15 on each before I hooked them back up. Through the day yesterday they both seemed to be discharging at the same rate until I checked them this AM. The battery with the lower rating is the one on the side of the positive connection to the inverter.
What am I doing wrong?
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Dillio187
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# Posted: 4 Jan 2014 09:39
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are they wired in series for 12V? If so, yes they should discharge at the same rate if the batteries are of the same age and in similar condition.
Have you checked the fluid level inside?
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MtnDon
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# Posted: 4 Jan 2014 10:48
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The assumption is they are series connected to provide 12 volts to the inverter. That means they should also be charged as a 12 volt bank of batteries.
Are they flooded cells with removable caps? If so get a good hydrometer so you can take actual specific gravity readings. Voltage readings can be misleading as to true state of charge. If using voltage the reading should be taken several hours after charging or any heavy discharging. 12 hours is best.
The 105 minutes at 75 amps figure does not mean much as you are using the batteries at a much lower discharge rate. The number you should look at is the amp-hour capacity at the 20 hour rate. Most 6 volt GC batteries are in the range of 210 - 225 amp-hours at the 20 hour rate. With the batteries in series that gives you 12 volts and 210-225 amp hours. You could do with a larger battery charger, one of 25 to 30 amps at 12 volts. That will charge the batteries quicker and save generator wear and tear as well as gas.
Rule of thumb for "best" charge rate is C/10 to C/8, where C= amp-hour Capacity of the batteries.
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MI drew
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# Posted: 4 Jan 2014 21:23
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Wow. Thanks for all the information. I just bought them on 12/30. They have the same date code and the water levels look just fine. The date code says M3. The 20 amp hour rating is 215. So I'm guessing March? With what your saying that I can charge them with 25-30 amps. I don't think I have really given them a full charge then. I'm at home now and have one on a 6v 15amp charge. I will do them sepperate until I have the full charge light come on the charger. Then I'll take some readings sepperate and hooked up in series together. This is my first experience with true deep cycle batteries. Up till now I have been using a 12v marine battery. I was surprised on how little time I was getting out of them. Also, it looks like I need to invest in another charger that will do 25-30 amps. I'm sure my 100 amp jump is too much.
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Dillio187
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# Posted: 5 Jan 2014 09:58
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when you are charging them at a good rate, you should be able to hear them gassing if it's quiet in the room, and if not quiet, pull the caps and you will see them bubble. This is good as it helps stir the electrolyte and break any build up off the plates.
Don is also right, charge them as a 12V bank, not separately as 6V batteries. 15 amps will charge the batteries, but will take longer. Also, it sounds like you are using an auto type charger, I would strongly recommend looking at a 3 or 4 stage charger meant for charging battery banks.
Also, your 1500 watt inverter likely has a fairly high rate of idle power draw. That is, even when you aren't using anything, the inverter is still powering itself and using amp hours. You might want to consider a smaller inverter like the Morningstar 300W true sine wave inverter for smaller loads, and use the bigger inverter for large loads.
Good luck!
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MI drew
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# Posted: 5 Jan 2014 11:32
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We have bubbles! I wasn't really even giving them a good charge that's for sure. I read up a little this morning and it looks like I need to be at 14v to even give them a decent charge. When I was at the cabin I was only at about 12.9 at the highest level. They have been on the charger all night now. So by my math at 215 x C/10 and C/8, I would be safe to charge them at 22 to 27 amps respectively. At the 15 amps I am currently using they should charge in about 14.3 hours from totally dead? My inverter states it will use .5amps at idle. I will be getting a proper charger for sure very soon... If not my genny would be running 4 ever. I also planned on getting a pure sine inverter. Thanks for the suggestion on the Morning Star. Being 10.5v is totally dead and something I do not want to do... is 12v or 12.3v the lowest limit I want to be at before charging? My plan this year is to get a couple panels this summer... i just don't want to kill them before then. Then again I do have 12mth replacement warranty.
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MI drew
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# Posted: 5 Jan 2014 11:35
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One more question. Will my charger get to full charge mode and then go to maintain them or is it not set up for that being they are true deep cycle batteries and not marine style? Do I risk overcharging them at 15amps?
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MtnDon
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# Posted: 5 Jan 2014 11:46 - Edited by: MtnDon
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Quoting: MI drew Will my charger get to full charge mode and then go to maintain
No way of telling that from a distance. If it is a simple auto charger the charge rate should slow as the charge in the battery approaches full. But if left too long it may continue gassing and using up water. Find or look up the manual; it's the best source of info.
Also buy a hydrometer, it is the best way to determine charge.
For best battery life you want a 4 stage charger; bulk, absorb, float and equalize. Read here about batteries
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Dillio187
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# Posted: 5 Jan 2014 16:35
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consider investing in a battery monitor and shunt. It will accurately measure amp hours in and out of your battery bank, will show you current voltage and amperage draw/charge as well. I have this one at home and at the cabin, and I love it.
http://www.solar-electric.com/tr20mosy.html
you don't ever want to take your batteries down to 10.5 volts, I wouldn't even want to see 11.x volts as that is really getting close to dead. You don't want to take your batteries below 50% or you really reduce their life. I start my generator to charge my batteries at 70% (or plug in my charger to the grid at home)
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MI drew
Member
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# Posted: 5 Jan 2014 19:34
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Well here is the answer. Yes it will go to float mode once they are at compacity. They were charging at 14.6 for a while until the green light came on. My charger is only a 3 stage. Thanks for all the information on the battery stuff. I will be doing some Internet ordering very soon. Can't wait to see what I can really get out of these now that their actually charged. I read that link MtnDon. Very informative and I love to learn about things. Makes sense. Also checked on my inverter and it only uses <.16 amps at idle. I was wrong at the .5 earlier.
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MI drew
Member
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# Posted: 8 Jan 2014 11:22
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The 2 batteries have been on float now for a couple days right at 12.98v. Things seem like the are going well. I ordered a hydrometer and will be testing as soon as I get it.
Before I start buying solar panels, charge controlers, etc.... do I want to go 12v or 24v? I really don't think I will be using too much power while I'm up on weekends and a few weeks a year. I would like to add either a 4.3cu ft or 10 cu ft fridge and just have it plugged in either when in use or possible all the time. I am looking at the Renogy website and from what they say I can get away with my 2 batteries + their 2 100w solar panels and charge controler. Or get 2 more 6v batteries, a 250w 24v solar panel, charge controler, and 24 inverter. Any advice on which way to go? Thanks
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Dillio187
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# Posted: 8 Jan 2014 11:28 - Edited by: Dillio187
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IMO, neither of your proposals will run a fridge very well with other loads. I have a 4 golf cart battery, 24V system here at home and I only run my fridge from it on sunny days when the sun is hitting my 700 watt array. On cloudy days and at night it draws the batteries down pretty fast, so I flip that circuit back to grid power before the sun sets.
Add onto that you are only using it on weekends, and you have to start it up and have the whole unit cool itself down and you will probably run into problems. The setup with the 4 batteries and 250 watt panel is much closer, but you want more than a 250W panel to recharge a 220ah 24V bank, 2 250 watt panels would be more like it.
You might have already mentioned this (sorry posting this on a tiny tablet!), do you have a generator for backup? Your setup could work but you will probably be running the generator and battery charger a fair amount to recharge your batteries.
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MI drew
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# Posted: 8 Jan 2014 12:00
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My bad.... I miss typed. I'm doing this from my cell. I meant to say off their calculator with my current set-up (lights, TV, etc) I could be fine with those two options. I am looking to add a fridge in the future. So as my system expands... 12v or 24v the better way to go? If I get the 2 x 100w panels they can wired for 12v or 24v and the charge controller will auto correct for both as well. The difference for the the 2 panels at 100w is $320 and the one 250w 24v panel is $249. I would need a new inverter right from the start with 24v + 2 more batteries at $170. I guess I could just go with the 2x 12v panels for now and change over the inverter once I get 2 more batteries. I'm guessing the 24w system is more efficient in the long run? This spring I plan on taking a solar class at my local comm college.
Also, I have a 6500w generator.
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Dillio187
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# Posted: 9 Jan 2014 09:56 - Edited by: Dillio187
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the 24V is definitely more efficient, plus you can get away with smaller wire sizes saving you some money on wire. Using ~30 volt panels, it is more efficient to step down 34 volts to 24 volts rather than 34 volts to 12 volts.
My advice would be to size your system now for whatever anticipated load you have. Solar setups do not grow real well so it's best to bite the bullet once and get what you want. I have heard dozens of stories about people buying panels or batteries with the plan to eventually get more, and when they decided to buy more, the model or type is no longer available.
Like you said, if you use a good MPPT charge controller, your bank can usually be 12 or 24V (and sometimes 48V depending on the controller). A lot can be said though about having a 12V bank at a cabin for jump starting vehicles and running 12V appliances.
Personally if I had to build my cabin system over again, I wouldn't bother with small solar panels, I would go right to the 235+ watt panels. They are the best bang for the buck at under 80 cents a watt on sale. A couple of those with an MPPT controller would be great, and make wiring and panel fusing easier.
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