Actually had a case where I was working a few weeks ago with a tractor not related to the op but farmer had three starting batteries connected in parallel but against my advice he had used a calcium battery with two other lead acid of course the calcium battery failed as the other two drained it over a few months period.
He said "but you said calcium batteries are better when being left for long periods" and yes they are but not mixed with dissimilar types that need charging monthly, now he thinks calcium or agm batteries are a waste of money, you just cannot get through to some people.
Same bloke bought a cheap you beaut 40 amp battery charger against my advice to get a c-tek, after destroying several batteries I cut the leads off it and told him again to buy a c-tek?
Battery question - solar charger
-
mastreb
- Admiral
- Posts: 3927
- Joined: Wed Feb 09, 2011 9:00 am
- Sailboat: MacGregor 26M
- Location: Cardiff by the Sea, CA ETEC-60 "Luna Sea"
- Contact:
Re: Battery question - solar charger
With all batteries of all types, resistance to charging goes up as the battery reaches its rated capacity. This effect causes all of the "battery mystery" that people are discussing in this thread: Incompatibility of different types, the difficulty in gang charging batteries, whether and how they level when connected together, etc.
By analogy, imagine you have a water container that is pressurized: You can add water or remove water from the bottom, but the air trapped in the container stays in the container at all times. It's at normal atmospheric pressure when empty, and so water floods in easily. As the air pressure increases as the container fills with water, the acceptance rate decreases. Eventually, the air pressure inside the container matches the fill pressure of the pipe you're using to add water, and the container will no longer take in water. It is full.
The reverse is also true: From full, the container will have the highest pressure (voltage) and that goes down as the container empties. For this reason, battery voltage goes down as charge depletes.
This analogy is useful for describing how a battery charges, and like electrical resistance, the pressurized container heats up as the air compresses due to Boyle's law (you've likely touched a hot air compressor at some point), but pressure heating is not as dramatically as electrical resistance.
In electrical systems, resistance always generates heat, which means that as a battery fills, it also warms up, and that heat is maximized when the battery is full. This is why charging batteries get warm to hot (depending on type and charging voltage). It's also why parallel charging doesn't work well across types: Because their resistance characteristics and capacities are different, the same charging voltage that one can easily accept will destroy one of a different type.
Electricity will always flow to the point of least resistance. Charging similar batteries in parallel sort of works for this reason, but as batteries age (due to heat) their capacity goes down, which means that their resistive heating increases at lower charge levels. If they don't age at exactly the same rate, one of the batteries in a gang will heat up more than others at the same charge rate, and will fail earlier. A single charge controller on a gang of batteries cannot detect this problem, because it's only looking at the average voltage across the entire gang.
It's also sort of true that one battery can charge another, but you lose a lot of power to resistive heating, an effect that is more dramatic if the types are different. Over time, they will reach equilibrium, but much of the original charge will have been lost to heat.
Charge controllers work by pulsing the charging power. The purpose of this is to minimize resistive heating both in the wires leading to the battery and in the battery itself. By giving the battery time to cool (actually, to not heat up in the first place) between bursts of electricity, acceptance remains higher and degradation due to heat is minimized, which increases battery life. So they charge faster, more safely, and with less degradation due to heating. Rectified alternators also produce pulsed power, providing a similar effect. Low power DC charging (<15 watts for a car battery) is fine without a charge controller because there's not enough power to cause much resistive heating, but anything higher than that should be pulsed by a charge controller or a rectified alternator.
While you can gang charge batteries of the same type and age safely, for maximum life of any battery regardless of type, and irrespective of how you gang batteries to get either multiplied voltage (series) or multiple amperage (parallel), you should charge batteries with individual controllers on each battery. This allows the controller to sense the battery levels and temperature individually and maximize their charge and life. If you don't do that, you will shorten the life of your batteries, but it may be more cost effective to replace batteries earlier than it is to build a sophisticating battery charging circuit.
By analogy, imagine you have a water container that is pressurized: You can add water or remove water from the bottom, but the air trapped in the container stays in the container at all times. It's at normal atmospheric pressure when empty, and so water floods in easily. As the air pressure increases as the container fills with water, the acceptance rate decreases. Eventually, the air pressure inside the container matches the fill pressure of the pipe you're using to add water, and the container will no longer take in water. It is full.
The reverse is also true: From full, the container will have the highest pressure (voltage) and that goes down as the container empties. For this reason, battery voltage goes down as charge depletes.
This analogy is useful for describing how a battery charges, and like electrical resistance, the pressurized container heats up as the air compresses due to Boyle's law (you've likely touched a hot air compressor at some point), but pressure heating is not as dramatically as electrical resistance.
In electrical systems, resistance always generates heat, which means that as a battery fills, it also warms up, and that heat is maximized when the battery is full. This is why charging batteries get warm to hot (depending on type and charging voltage). It's also why parallel charging doesn't work well across types: Because their resistance characteristics and capacities are different, the same charging voltage that one can easily accept will destroy one of a different type.
Electricity will always flow to the point of least resistance. Charging similar batteries in parallel sort of works for this reason, but as batteries age (due to heat) their capacity goes down, which means that their resistive heating increases at lower charge levels. If they don't age at exactly the same rate, one of the batteries in a gang will heat up more than others at the same charge rate, and will fail earlier. A single charge controller on a gang of batteries cannot detect this problem, because it's only looking at the average voltage across the entire gang.
It's also sort of true that one battery can charge another, but you lose a lot of power to resistive heating, an effect that is more dramatic if the types are different. Over time, they will reach equilibrium, but much of the original charge will have been lost to heat.
Charge controllers work by pulsing the charging power. The purpose of this is to minimize resistive heating both in the wires leading to the battery and in the battery itself. By giving the battery time to cool (actually, to not heat up in the first place) between bursts of electricity, acceptance remains higher and degradation due to heat is minimized, which increases battery life. So they charge faster, more safely, and with less degradation due to heating. Rectified alternators also produce pulsed power, providing a similar effect. Low power DC charging (<15 watts for a car battery) is fine without a charge controller because there's not enough power to cause much resistive heating, but anything higher than that should be pulsed by a charge controller or a rectified alternator.
While you can gang charge batteries of the same type and age safely, for maximum life of any battery regardless of type, and irrespective of how you gang batteries to get either multiplied voltage (series) or multiple amperage (parallel), you should charge batteries with individual controllers on each battery. This allows the controller to sense the battery levels and temperature individually and maximize their charge and life. If you don't do that, you will shorten the life of your batteries, but it may be more cost effective to replace batteries earlier than it is to build a sophisticating battery charging circuit.
-
DaveB
- Admiral
- Posts: 2543
- Joined: Mon Jan 07, 2008 2:34 pm
- Sailboat: MacGregor 26X
- Location: Cape Coral, Florida,1997 Mac. X, 2013 Merc.50hp Big Foot, sold 9/10/15
Re: Battery question - solar charger
Thats why you use a combiner to keep batteries seperate and charge independently and not have one faulty battery discharge to others.
http://www.yandina.com/c100InfoR3.htm
Dave
http://www.yandina.com/c100InfoR3.htm
Dave
mastreb wrote:With all batteries of all types, resistance to charging goes up as the battery reaches its rated capacity. This effect causes all of the "battery mystery" that people are discussing in this thread: Incompatibility of different types, the difficulty in gang charging batteries, whether and how they level when connected together, etc.
Last edited by kmclemore on Sat May 18, 2013 7:17 pm, edited 1 time in total.
Reason: Fixed quote.
Reason: Fixed quote.
-
Boblee
- Admiral
- Posts: 1702
- Joined: Thu Aug 10, 2006 5:08 am
- Location: Berrigan, Riverina Australia boatless at present
Re: Battery question - solar charger
Love the analogy of the pressured container but like all these analogies used to try and explain things in simple terms for the layman people can take them literally.
When I was a first year apprentice the boss came out laughing his head off, he had explained that electricity was like water to an old lady that had just moved into town and never had power before but being off the land she was fairly practical.
She had bumped a globe on a drop pendant (flexible cord) and it had broken so she wanted us down there asap but she had tied a knot in the cord so the electricity (water) wouldn't leak out so it would be ok till we got there.
Bartmac another very good explanation like your work it's always very hard to send the message in simple terms without confusing the issue but you did a great job.
Unfortunately most of the problems I have found when travelling have originated from auto elecs who should know better.
When I was a first year apprentice the boss came out laughing his head off, he had explained that electricity was like water to an old lady that had just moved into town and never had power before but being off the land she was fairly practical.
She had bumped a globe on a drop pendant (flexible cord) and it had broken so she wanted us down there asap but she had tied a knot in the cord so the electricity (water) wouldn't leak out so it would be ok till we got there.
Bartmac another very good explanation like your work it's always very hard to send the message in simple terms without confusing the issue but you did a great job.
Unfortunately most of the problems I have found when travelling have originated from auto elecs who should know better.