Killed my Batteries, starting over

jmiller968 · August 2015

Hello!

A quick breakdown of my situation: Remote cabin, wired for electricity, but no means to connect to the grid. Currently used on weekends in the summer and maybe once or twice during the winter. Electric use limited to lights (mostly led bulbs, a few cfl), a radio, LED television and dvd player. I also run a dc RV pump for water. Max day would be 1000 watt hrs.

I have been using a honda generator (1000i), 2 6v AGM batteries (220 amp hour), and a suresine inverter. I typically run on batteries during the day, and run the generator in the evening to power the cabin and recharge the batteries via an IOTA DLS30 with an IQ4. This has worked out fine for all last year, and half of this year. But now my batteries appear to be shot. The voltage still seems high, but quickly drops when a load is placed on them.

I am assuming that the problem was that I never fully recharged the batteries. Most of the time I only ran the generator for a few hours, which just bulked them up, so they have spent most of their short lives in a state of partial charge. I am beginning to understand that this is not desirable?

So, I am beginning to realize that I need to hook up some solar to keep the batteries topped off. My current plan is to replace the 2 AGM batteries with 4 wet cell 6v batteries(215 amp hour). Assuming that sounds reasonable, what should I be looking for in solar panels and charge controller? One drawback is that I don't get any sun on the cabin(can't cut trees...shoreland zone), and would have to place the panels down by the lake, which is approximately 200 feet away from where the batteries would be. I was looking at a 400w kit from renogy, but according to their calculator I would need 6 ga wire from the panels to the charge controller! At that rate I would be paying more for wire than Panels!

Anyway, any help or guidance would be appreciated.

Thank You!

westbranch · August 2015

my lake neighbour has a 20 foot pole with 4 140w panels on it.batteries in an enclosure near by and sends 120V ac to the cabin.. yes that is the issue with distance, further away the larger the wire needed is... get an MPPT CC and run all 4 in series to have the highest voltage and lowest amperage and let the MPPT kick it down to 12 v if you want to leave the bats close to the cabin...

hth

Apples · August 2015

I am assuming that the problem was that I never fully recharged the batteries. Most of the time I only ran the generator for a few hours, which just bulked them up, so they have spent most of their short lives in a state of partial charge. I am beginning to understand that this is not desirable?

Bingo. Batteries should remain in absorption for at least 3 or 4 hours. In the case of the better brand of AGM, 4 to 6 hours and at 14.6-14.7 volts for absorption.

Unless your batteries were chronically discharged to a 0% state of charge (easily done in a scenario such as yours when they're never fully charged), your latest diagnosis is correct. I have had to learn this from similar experience.

Be sure, also, to have the batteries as close as possible to the charge controller and use enough wire diameter to do so. A controller's output voltage won't travel far in thin wire... which can be just one of the causes of undercharging. The other is an absorb voltage setpoint too low.

Westbranch made an excellent suggestion of installing the batteries closer to the panels then after inversion to 120V you may simply run standard heavy-duty (12 ga minimum) power cord from there to the cabin. Even then you'll need to be sure you have enough wire diameter.

Here's a voltage drop calculator to aid in wire-size selection. For our needs, input "copper" stranded, and "overhead" (unless you're burying the cable) and 3% limit on losses...

PNjunction · August 2015

Before you do all that, you may want to look into a 12v Tecmate-Optimate 6 model tm-181 charger. Supports up to 240ah

Obviously this is too small for regular cyclic use. What I would do is bulk the system a bit, (batteries disconnected from system) and then throw the Optimate 6 on it and let it do it's thing. That might mean running your genny to power the inverter / optimate for quite awhile, but might be worth it to you for a recovery effort.

Out of all the joke recovery battery chargers out there, only the Optimates lived up to their claims for me. Watching them with high-end Fluke gear reassured me that they know what they are doing. And it gives you a testing result to see what state the recovery left the batteries in. They are refreshingly honest - it won't recover the absolutely abused battery that is basically a waste-case.

I'll stop the anecdotal internet salesmanship here. Check out their online manual to see what's up. I own FIVE different versions now.

Like I mentioned before, this is not something to regularly cycle with on large batteries, but if anything has a chance of bringing things back from abuse, especially agm's, these have proven themselves to me. The fact that your batteries are still somewhat functional, just sulfated, and have not been sitting dead in a garage for 5 years for that sulfate to harden like diamonds, provoked me to comment.

vtmaps · August 2015

jmiller968 wrote: »

plan is to replace the 2 AGM batteries with 4 wet cell 6v batteries(215 amp hour). Assuming that sounds reasonable, what should I be looking for in solar panels and charge controller?

Welcome to the forum.

As a general rule of thumb we recommend a 5% - 13% charge rate of the batteries. Being that you have only occasional use of the cabin, and that you have a generator, you can get by with the lower end of those rates. Your battery bank will be 430 ah at 12 volts. At the 5% charge rate (of 430 ah) you should aim for 21.5 amps of charging current. 21.5 amps X 12 volts is 258 watts of charging power. Of course, your panels and charge controller must be derated (they are not 100% efficient) and your goal of 400 watts of panel is more than adequate to achieve a 5% charge rate.

Next issue is the distance between the panels and the battery. Westbranch's solution of putting all the panels in series and running high voltage to an MPPT controller in the cabin is good, but there are some caveats. Don't let the voltage get too high, for two reasons: 1) when cold the Voc is increased above specification and may damage your controller, and 2) your controller is less efficient at high input voltages, and this causes heat in the controller.

I suggest that you look for 2 panels with Vmp = 37 volts, and put them in series. For example two of these panels in series with 10 gauge cable to the controller will give you a very acceptable voltage drop. If you can find 3 panels with Vmp of 30 volts and put them in series, that will also work, but it may be hard to find Vmp = 30 panels in such low wattages.

Get a controller that is over-rated for the current that you will be supplying to the batteries... you will be using the controller inefficiently because of your high input voltage and therefore you do not want it to be at the limits of its power handling capacity. Make sure your controller can handle the high Voc in cold weather (I don't know where your cabin is located).

--vtMaps

lkruper · August 2015

jmiller968 wrote: »

Hello!

A quick breakdown of my situation: Remote cabin, wired for electricity, but no means to connect to the grid. Currently used on weekends in the summer and maybe once or twice during the winter. Electric use limited to lights (mostly led bulbs, a few cfl), a radio, LED television and dvd player. I also run a dc RV pump for water. Max day would be 1000 watt hrs.

I have been using a honda generator (1000i), 2 6v AGM batteries (220 amp hour), and a suresine inverter. I typically run on batteries during the day, and run the generator in the evening to power the cabin and recharge the batteries via an IOTA DLS30 with an IQ4. This has worked out fine for all last year, and half of this year. But now my batteries appear to be shot. The voltage still seems high, but quickly drops when a load is placed on them.

I am assuming that the problem was that I never fully recharged the batteries. Most of the time I only ran the generator for a few hours, which just bulked them up, so they have spent most of their short lives in a state of partial charge. I am beginning to understand that this is not desirable?

So, I am beginning to realize that I need to hook up some solar to keep the batteries topped off. My current plan is to replace the 2 AGM batteries with 4 wet cell 6v batteries(215 amp hour). Assuming that sounds reasonable, what should I be looking for in solar panels and charge controller? One drawback is that I don't get any sun on the cabin(can't cut trees...shoreland zone), and would have to place the panels down by the lake, which is approximately 200 feet away from where the batteries would be. I was looking at a 400w kit from renogy, but according to their calculator I would need 6 ga wire from the panels to the charge controller! At that rate I would be paying more for wire than Panels!

Anyway, any help or guidance would be appreciated.

Thank You!

It appears your 1000wh / day is not too much for your battery bank (35% DOD) but if the reason you only run your generator for a few hours per night is the noise I understand. If not, then you can fix the problem without increasing battery capacity or adding solar.

However if it was me I agree that having enough extra battery capacity to span the weekend (you will be discharged no more than 40 % at the end of a 2 day weekend) means not listening to the generator unless you are fixing a problem. 5 days between visits should give enough time to recharge the batteries with solar.

You may want to consider Trojans new RE flooded T105s which claim to have a formula to mitigate a battery that is not fully charged. Size your charge controller to provide the maximum charge rate your battery recommends and get a charger with temperature compensation.

jmiller968 · August 2015

Thanks for all the great input folks, this is helping out tremendously. I am going to go ahead and order the Optimate, thanks for that tip PNjunction. I have another building that I can use those AGM batteries in if I can resurrect them. Westbranch's suggestion on moving the charge controller out to the panels is a great one, but I really like where my batteries are now, and if I move them I am also going to have to run wire for my DC loads. So I think the solution is wiring them in Series. Assuming that I get the panels VTmap recommended, can you recommend a decent MPPT controller that won't break the bank? I am up in Maine, so cold will be an issue.

On another note...the batteries are currently under cabin, protected from rain/snow/wind, but still outside. Can they ride out the winter like that? Should I pull them off, build an insulated box? Part of the reason I got the AGM batteries to begin with was that I thought I could just leave them. Not sure about the flooded batteries. The cabin is on an island, which makes moving batteries a painful process.

Thanks again guys, you are great!

lkruper · August 2015

jmiller968 wrote: »

Thanks for all the great input folks, this is helping out tremendously. I am going to go ahead and order the Optimate, thanks for that tip PNjunction. I have another building that I can use those AGM batteries in if I can resurrect them. Westbranch's suggestion on moving the charge controller out to the panels is a great one, but I really like where my batteries are now, and if I move them I am also going to have to run wire for my DC loads. So I think the solution is wiring them in Series. Assuming that I get the panels VTmap recommended, can you recommend a decent MPPT controller that won't break the bank? I am up in Maine, so cold will be an issue.

On another note...the batteries are currently under cabin, protected from rain/snow/wind, but still outside. Can they ride out the winter like that? Should I pull them off, build an insulated box? Part of the reason I got the AGM batteries to begin with was that I thought I could just leave them. Not sure about the flooded batteries. The cabin is on an island, which makes moving batteries a painful process.

Thanks again guys, you are great!

Batteries should not be charged when they are frozen and batteries that are fully charged won't freeze easily. What you should do, however, is to make sure your charger has temperature compensation. Batteries like the same temperatures people do, and the charge voltage needs to be adjusted based on temperature. Your batteries will last longer. Battery boxes are nice and if you get very low temperatures they could be insulated. However boxes are also for safety to contain acid should a battery explode and also vented to expel any hydrogen gas during charging. However if your area is well ventilated (the basement under my cabin leaks like a sieve) you may not need them.

BB. · August 2015

A fully charged lead acid battery can go below ~ -70F without freezing (freezing a flooded cell battery will ruin it--AGMs may survive freezing--But you cannot charge/discharge a "frozen" battery).

So, if the cabin sits unused--Fully charging the battery and mounting a solar panel vertical/on a wall to float the bank through winter (roughly 1% to 2% minimum rate of charge). A fully charged/unused lead acid battery bank at 0F is a very happy battery bank.

A few folks that visit cabins in the winter will use a small genset + battery heater (for those guys in the great white north) and heat the batteries for 8-24 hours to 32F+ in a thermal box. After the batteries are "warm"--Then normal cycling (charging/discharging) will keep the batteries warm enough for satisfactory operation.

-Bill

vtmaps · August 2015

jmiller968 wrote: »

can you recommend a decent MPPT controller that won't break the bank? I am up in Maine, so cold will be an issue.

You want an MPPT controller that can handle AT LEAST 30 amps output, and can handle 125% of the Voc of your panels in series. The Midnite kid qualifies as does the Morningstar Tristar 30 MPPT. Morningstar also makes a 45 amp Tristar MPPT for a few dollars more. If they break the bank, that is the price you pay for placing your panels 200 ft from your controller... no free lunch

Either of those controllers will be able to handle twice the array and be more efficient if you ever upgrade your batteries to 24 volts.

--vtMaps

PNjunction · August 2015

jmiller968 wrote: »

Thanks for all the great input folks, this is helping out tremendously. I am going to go ahead and order the Optimate, thanks for that tip PNjunction. I have another building that I can use those AGM batteries in if I can resurrect them.

Nice - could be a cheap solution for the time being. If you can't get any results from it, it will make an awesome vehicle battery charger / preventative maintenance charger, so you aren't wasting money. I would disconnect the battery from all your other gear in order for it to do the best it can.

Westbranch's suggestion on moving the charge controller out to the panels is a great one, but I really like where my batteries are now, and if I move them I am also going to have to run wire for my DC loads.

I'm pretty sure he meant the batteries. Charge controllers need to be very close to the batteries. Usually this is for adequate temperature compensation to be similar to the environment your batteries are in (if just ambient control), or you can use "on the battery" temp probes, which are even better. In addition, voltage drop needs to be as small as it can from the controller to the batteries - hence the use of short runs and adequate gauge. Otherwise, the "14.4v" you set up for on the charge controller may in reality turn out to be only 14.2v or lower "at the battery terminals", which will not do most agm's any good.

The others have commented on possible upgrades, and they are good.

Killed my Batteries, starting over

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