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Old 01-05-2015, 07:02   #16
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Re: Use a normal car battery for solar panel?

Your 100 watt solar panel will probably produce at least 300-400 watt/hours worth of charging on a normal, mostly sunny day. Perhaps as much as 400-500. So if your estimate of your usage is accurate, you should have no problems at all.
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Old 01-05-2015, 07:06   #17
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Re: Use a normal car battery for solar panel?

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Your 100 watt solar panel will probably produce at least 300-400 watt/hours worth of charging on a normal, mostly sunny day. Perhaps as much as 400-500. So if your estimate of your usage is accurate, you should have no problems at all.
Yeah that's what I also figured, I was just worried if the batteries aren't deep cycle and I spend up lets say 150watt in the evening (with no charge), then that puts a car battery considerably below it's optimal 'state of charge' and wondered how much of a negative effect that will have of its life.

That's actually the reason why I wanted to get an AGM house battery, as I could then easily spend power in the evening without having to worry about the discharge getting down to 50-70%.
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Old 01-05-2015, 07:10   #18
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Re: Use a normal car battery for solar panel?

Hi Nick

As others have said, with your very minimal power needs most any old battery will do the trick. On that basis, no point in spending the big bucks for AGM.

Also true that a "starting" battery likes to stay charged but would still probably last for a few years as long as you don't discharge it really low and leave it that way. A deep cycle battery would be better but not sure if a true deep cycle battery is made in the small size you would need. There are small batteries, like group 27 size or similar that are called "marine" or "deep cycle" batteries but from what I know those are not true deep cycle but kind of a compromise. Still would probably be a better option for house power for you.

Since you have an inboard diesel you will also need some battery power for starting. Does the boat have only the one or does it have one for starting and another for house loads? If only one battery and it was my boat, adding a second dedicated just for engine cranking would be a priority although I think some of the old Volvos were set up to hand crank.
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Old 01-05-2015, 07:16   #19
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Re: Use a normal car battery for solar panel?

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Yeah that's what I also figured, I was just worried if the batteries aren't deep cycle and I spend up lets say 150watt in the evening (with no charge), then that puts a car battery considerably below it's optimal 'state of charge' and wondered how much of a negative effect that will have of its life.

That's actually the reason why I wanted to get an AGM house battery, as I could then easily spend power in the evening without having to worry about the discharge getting down to 50-70%.
Assuming 75amp-hr batteries, using 12-15amp-hrs should be fine. You can go from 100% to 50% without too much concern. Often there is an assumption that you have around 30% of the rated amp-hrs as charging slows down after you reach 80% of capacity so you often don't get that last few percentage points. If you get a few cloudy days in a row, you will get significantly less charging but you can always run the engine for an hour or two if you start getting low.

You can still kill AGM batteries by discharging them to low, so don't simply assume that you can just install and ignore them. In fact, in some ways they are more sensative to abuse from incorrect charging.
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Old 01-05-2015, 07:21   #20
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Re: Use a normal car battery for solar panel?

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Hi Nick

As others have said, with your very minimal power needs most any old battery will do the trick. On that basis, no point in spending the big bucks for AGM.

Also true that a "starting" battery likes to stay charged but would still probably last for a few years as long as you don't discharge it really low and leave it that way. A deep cycle battery would be better but not sure if a true deep cycle battery is made in the small size you would need. There are small batteries, like group 27 size or similar that are called "marine" or "deep cycle" batteries but from what I know those are not true deep cycle but kind of a compromise. Still would probably be a better option for house power for you.

Since you have an inboard diesel you will also need some battery power for starting. Does the boat have only the one or does it have one for starting and another for house loads? If only one battery and it was my boat, adding a second dedicated just for engine cranking would be a priority although I think some of the old Volvos were set up to hand crank.
Hi,

Yeah it has a hand crank as well in worst case

It does have 2 batteries, one start and one house. I am just not sure how he has wired it all, I will first be able to really check that once I get on the boat.

I purchased it in Sweden, so I got a 1-2 weeks trip back home with it (we want to enjoy the swedish coast as we are in no rush). But for that period it's important that we can charge and use our electronic devices. So this is really about checking up what things I need to bring with me for the installation. (If I needed to get an AGM battery and wire that up)

From what I've learned here, it probably won't be neccesary to add the AGM battery for now.

At some point I might also want to add a fridge and some other fancy stuff, so when that comes I need a better battery bank anyways. But that's first in the future.

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Originally Posted by valhalla360 View Post
Assuming 75amp-hr batteries, using 12-15amp-hrs should be fine. You can go from 100% to 50% without too much concern. Often there is an assumption that you have around 30% of the rated amp-hrs as charging slows down after you reach 80% of capacity so you often don't get that last few percentage points. If you get a few cloudy days in a row, you will get significantly less charging but you can always run the engine for an hour or two if you start getting low.

You can still kill AGM batteries by discharging them to low, so don't simply assume that you can just install and ignore them. In fact, in some ways they are more sensative to abuse from incorrect charging.
That's good to know. I was worried that if I pushed the car battery below 90% then it would explode and kill me and my passengers No, not that extreme, but I thought it would ruin the battery within a couple of days.
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Old 01-05-2015, 08:32   #21
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Re: Use a normal car battery for solar panel?

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That's good to know. I was worried that if I pushed the car battery below 90% then it would explode and kill me and my passengers No, not that extreme, but I thought it would ruin the battery within a couple of days.
Oh absolutely. If you discharge a starting battery to 89.99% your boat will immediately turn into a raging, flaming inferno.

Seriously, you can discharge a standard car starting battery to dead flat zero and leave it like that for a couple of weeks and it will still probably recharge and have enough capacity left for light weight loads.

Know this from personal experience after my wife left the lights on in the car when she parked it at the airport on the way to a two week trip. Got back it was as dead as dead could be. Got a jump, cranked up and by the time we got home it was charged up and would start the car easily. However it definitely lost a lot of capacity. Run the radio or lights for a couple of hours would be enough to run the battery down. But we still used it for another 2-3 years before it died altogether.

Since you're in Europe I hear a lot of the small caravans and such buy what they call a leisure battery. From what I can tell that's a standard FLA that is kind of deep cycle. Could be OK for you for now, at least until you install that 12V fridge. FYI for a most cruisers the fridge is by far the biggest power user on the boat. Be prepared to do some serious upgrades to the whole electrical system: batteries, charging, wiring and everything in between.
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Old 01-05-2015, 09:32   #22
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Re: Use a normal car battery for solar panel?

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Since you're in Europe I hear a lot of the small caravans and such buy what they call a leisure battery. From what I can tell that's a standard FLA that is kind of deep cycle. Could be OK for you for now, at least until you install that 12V fridge. FYI for a most cruisers the fridge is by far the biggest power user on the boat. Be prepared to do some serious upgrades to the whole electrical system: batteries, charging, wiring and everything in between.
I believe what they categorize as leisure batteries are just simple gel-batteries. I've also seen a lot of batteries being called "Solar batteries" but are really just GEL/AMG branded differently. - I'm not sure on this though

Yeah a fridge is heavy-duty. I'll probably go with a compressor coolbox (CFX series from Waeco). Seems like it has a relatively low avr. powerdraw (0.6amps according to their specs). Of course circumstances vary, but seems very efficient.
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Old 01-05-2015, 09:39   #23
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Re: Use a normal car battery for solar panel?

my batteries are from o'rileys, I charge them with my solar panel. as long as you have a controller that turns off the voltage when it reaches 12.9 your batteries will last a longtim
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Old 01-05-2015, 09:40   #24
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Re: Use a normal car battery for solar panel?

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That's actually the reason why I wanted to get an AGM house battery, as I could then easily spend power in the evening without having to worry about the discharge getting down to 50-70%.
But once again, based on the words you are using, I'm not sure that you understand that what you want is a deep-cycle battery. Whether that is an AGM deep-cycle battery, or a lead-acid deep-cycle battery, or a gel deep-cycle battery really doesn't matter. There are various reasons for wanting one or the other of these, but the important point is that it be a deep-cycle battery. Perhaps this is a language thing; you seem to be using "AGM" as if it means the same thing as "deep-cycle," but it does NOT.

Another way to say this... Not all deep-cycle batteries are AGM batteries. And just because a battery is AGM does not necessarily mean that it must be made for deep-cycle service. "Deep-cycle" describes the intended usage of the battery. "AGM" simply describes the particular construction of the battery, but does NOT mean that it is deep-cycle.

What you want, when you get around to replacing the batteries that you have, is a deep-cycle battery for house loads. If your choice is also that the battery should be AGM, that's fine. But that is a separate matter. First and foremost, you want the battery to made for deep-cycle service.
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Old 01-05-2015, 09:48   #25
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Re: Use a normal car battery for solar panel?

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But once again, based on the words you are using, I'm not sure that you understand that what you want is a deep-cycle battery. Whether that is an AGM deep-cycle battery, or a lead-acid deep-cycle battery, or a gel deep-cycle battery really doesn't matter. There are various reasons for wanting one or the other of these, but the important point is that it be a deep-cycle battery. Perhaps this is a language thing; you seem to be using "AGM" as if it means the same thing as "deep-cycle," but it does NOT.

Another way to say this... Not all deep-cycle batteries are AGM batteries. And just because a battery is AGM does not necessarily mean that it must be made for deep-cycle service. "Deep-cycle" describes the intended usage of the battery. "AGM" simply describes the particular construction of the battery, but does NOT mean that it is deep-cycle.

What you want, when you get around to replacing the batteries that you have, is a deep-cycle battery for house loads. If your choice is also that the battery should be AGM, that's fine. But that is a separate matter. First and foremost, you want the battery to made for deep-cycle service.
No no, I understand what a deep-cycle battery is. I also know there are different types, for me the AGM deep cycle battery just makes most sense price per watt wise from where I am located. Which is why I keep mentioning that I am going to use an AGM battery(for deep cycle)

I was however under the impression that car-batteries are mainly starter batteries and not intended for deep cycle use, which is why I wanted to change the batteries first of all.

- If the batteries aboard aren't deep cycle, then I wanted to know if I would still be able to use them to 50-70% discharge (which it seems I can). But of course with the cost of wearing down the batterys life faster.

Hope that makes sense.
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Old 01-05-2015, 09:49   #26
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Re: Use a normal car battery for solar panel?

With your stated loads and charging ( solar and alternator) you will be just fine probably for many years. Here's one thing to consider as far as future battery replacement fla batteries are almost idiot proof as long as you keep the water up and have a charge controlver charged. Agm batteries are much more sensitive to how they are charged. When the time comes to replace I would recommend 2 6 volt golf cart batteries. Due to price and great ah capacity for the price. ( bang for the buck) I have been using a pair in my RV for over ten years and they are still going strong .
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Old 01-05-2015, 09:55   #27
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Re: Use a normal car battery for solar panel?

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With your stated loads and charging ( solar and alternator) you will be just fine probably for many years. Here's one thing to consider as far as future battery replacement fla batteries are almost idiot proof as long as you keep the water up and have a charge controlver charged. Agm batteries are much more sensitive to how they are charged. When the time comes to replace I would recommend 2 6 volt golf cart batteries. Due to price and great ah capacity for the price. ( bang for the buck) I have been using a pair in my RV for over ten years and they are still going strong .
I've heard that from a couple of people. Could you send me a link to which would be suitable? I've found a wide range of 6v batteries, but they seem to all have really low capacities, so I'm not sure i'm looking the right places.

How about their discharging levels? Can they be completely discharged or how do they work differently to say a regular gel/agm battery?
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Old 01-05-2015, 10:07   #28
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Re: Use a normal car battery for solar panel?

start vs house batts...starting batts have thin plates to let off electrons fast to start an engine, deep cycle batts have thick plates so after years of re-charging, the thick plates will take the charging stress, they also let off the electrons slower, for lites, etc...i never let my house batts get below 12.5 volts, ie, half discharged! by not letting the batts get below 12.5v, their life is extended...always use distilled water, check often, fill up to the bottom of the plastic tube in the hole! check the connections often too! i don`t use the normal round post batts, i order mine with either holes in the post, or what is called 'L' brackets to bolt the fittings to...i also use an external regulator by ample power, here in seattle...i tried balmar for 5 yrs, and balmar had to replace mine every yr! finally got smart, and went to ample power...they work, and work, etc!...any questions, just ask...clyde
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Old 01-05-2015, 10:11   #29
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Re: Use a normal car battery for solar panel?

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I've heard that from a couple of people. Could you send me a link to which would be suitable? I've found a wide range of 6v batteries, but they seem to all have really low capacities, so I'm not sure i'm looking the right places.

How about their discharging levels? Can they be completely discharged or how do they work differently to say a regular gel/agm battery?
The top of the line deep cycle batteries are the Trojan T-105. Rolls Royce also makes a top end deep cycle and I think also in 6V. The Trojan size designation is the GC2 which is standard size and available in other brands as well. Look for a GC2 size golf cart battery if Trojans are not available. Not sure about over there but in the states you can find generics very close in quality to the Trojans for under $100 each.

The T-105 and similar deep cycles are rated around 220 amp hours at 6V. Connect two in series you get 220 amp hours at 12 V.

General practice even deep cycle batteries for max life don't discharge below 50% capacity. Occasional deeper discharge IF you recharge fully right away won't kill the battery.
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Old 01-05-2015, 10:15   #30
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Re: Use a normal car battery for solar panel?

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The top of the line deep cycle batteries are the Trojan T-105. Rolls Royce also makes a top end deep cycle and I think also in 6V. The Trojan size designation is the GC2 which is standard size and available in other brands as well. Look for a GC2 size golf cart battery if Trojans are not available. Not sure about over there but in the states you can find generics very close in quality to the Trojans for under $100 each.

The T-105 and similar deep cycles are rated around 220 amp hours at 6V. Connect two in series you get 220 amp hours at 12 V.

General practice even deep cycle batteries for max life don't discharge below 50% capacity. Occasional deeper discharge IF you recharge fully right away won't kill the battery.
Thanks for the model names, I'll look further into those!

What exactly is the advantage of running 2 of those in series, compared to just having a 220amp 12v battery? I seem to be missing that
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