Posted: 5/6/2010 4:04:27 AM EDT
|
I have a pump attached to 85 Amp hour battery. The pump is marked 11 Amps.
I read that I should not use more than half of the battery capacity. So, the available capacity is 42 Amp hour. Does this mean, I can continously use the pump for 42/11 = 3.818 hours? Is it possible for the pump to draw more than 11 Amps? The reason I ask is that the battery only last about 30 minutes before requiring new charge. Is the battery bad? |
|
Quoted:
Does this mean, I can continously use the pump for 42/11 = 3.818 hours? Yes, but only in theory. With a large load (and 11 amps is a pretty large load for a 85 AH battery), the effective AH capacity of the battery is reduced. Is it possible for the pump to draw more than 11 Amps? The reason I ask is that the
battery only last about 30 minutes before requiring new charge. Is the battery bad? Several possibilities: 1. The battery may be bad. 2. The battery may not be receiving a complete recharge. 3. The pump may require a much higher voltage than the battery is capable of continuously delivering. Most battery manufacturers define the AH capacity of their products as the point where the output drops to 10.5 volts. Obviously, if the pump stops working when the battery voltage drops to 11.25 volts, you won't be able to use the battery's full capacity with that pump. |
|
Start with a fresh battery - Costco has cheap ones Quoted: Quoted: Does this mean, I can continously use the pump for 42/11 = 3.818 hours? Yes, but only in theory. With a large load (and 11 amps is a pretty large load for a 85 AH battery), the effective AH capacity of the battery is reduced. Is it possible for the pump to draw more than 11 Amps? The reason I ask is that the battery only last about 30 minutes before requiring new charge. Is the battery bad? Several possibilities: 1. The battery may be bad. 2. The battery may not be receiving a complete recharge. 3. The pump may require a much higher voltage than the battery is capable of continuously delivering. Most battery manufacturers define the AH capacity of their products as the point where the output drops to 10.5 volts. Obviously, if the pump stops working when the battery voltage drops to 11.25 volts, you won't be able to use the battery's full capacity with that pump. |
|
Quoted:
Quoted:
Does this mean, I can continously use the pump for 42/11 = 3.818 hours? Yes, but only in theory. With a large load (and 11 amps is a pretty large load for a 85 AH battery), the effective AH capacity of the battery is reduced. Is it possible for the pump to draw more than 11 Amps? The reason I ask is that the
battery only last about 30 minutes before requiring new charge. Is the battery bad? Several possibilities: 1. The battery may be bad. 2. The battery may not be receiving a complete recharge. 3. The pump may require a much higher voltage than the battery is capable of continuously delivering. Most battery manufacturers define the AH capacity of their products as the point where the output drops to 10.5 volts. Obviously, if the pump stops working when the battery voltage drops to 11.25 volts, you won't be able to use the battery's full capacity with that pump. Thanks for the explanation. |
|
The above is good info. However, I will add that a quality and new battery should easily meet 50% of it's amp hour rating at 10% of it's rated AH load.
11 amps is in fact a high load for a 85AH battery. It's right in the ballpark for expected loads for a industrial battery that size. With intermittent use. Here is how it's generally figured: The standard is the 20 hour rate. Used for nearly every commonly available battery. The solar standard is the 100 hour rate, often used for large battery banks, expected to last many years. Generally with very low loads. The industrial rate is the 6 hour rate. This is where you are. So, 11 x 6 = 66, so you need, at minimum, (Remember the 50% rule) a 132AH industrial battery to run your pump for 6 hours. |
|
Quoted:
The above is good info. However, I will add that a quality and new battery should easily meet 50% of it's amp hour rating at 10% of it's rated AH load. 11 amps is in fact a high load for a 85AH battery. It's right in the ballpark for expected loads for a industrial battery that size. With intermittent use. Here is how it's generally figured: The standard is the 20 hour rate. Used for nearly every commonly available battery. The solar standard is the 100 hour rate, often used for large battery banks, expected to last many years. Generally with very low loads. The industrial rate is the 6 hour rate. This is where you are. So, 11 x 6 = 66, so you need, at minimum, (Remember the 50% rule) a 132AH industrial battery to run your pump for 6 hours. Thanks. As matter of fact, I went to Autozone last night and bought 105AH battery (biggest they had but twice the price). I just need to run the pump for 1 hour or less every day. With 1.5 Amp charger, I think it should fill up 11 Amp I use in less than 8 hours, right? |
|
Quoted:
With 1.5 Amp charger, I think it should fill up 11 Amp I use in less than 8 hours, right? Probably take a little longer than that, since the battery charging process is never 100 percent efficient. Some of the charging current is wasted, so the charger has to run a little extra to make up for it. |
|
A lot of it depends on this question: How often do you use the thing?
If you're cycling the battery every day, then how deeply you cycle it will be a huge factor. If it's a couple of times each year, then it becomes much less of a factor. Also, "fully discharged" does not mean "until the battery dies". It means until you get to the rated voltage (which will, actully, depend on the amp-draw you're placing the battery under at the time) If you only go to that point, even regular batteries will generally take a surprising number of "full discharges". The construction of a battery also matters. The thicker the plates, the more sulfation it takes before a battery is completely dead. Car batteries have very thin plates. Deep cycle batteries are a little thicker. Golf cart batteries even thicker. Each increase in plate thickness gives you more discharge cycles. If you're going to spring for a new battery.... go to Sam's and pick up a 100AH golf cart battery. It will hold up significantly better than a 100AH car battery, or even a 100AH deep cycle battery. If you want to get even more capacity... pick up two 6V, 200AH batteries and put them in series. |
|
The golf cart battery is a good idea, they're made for something like your application.
The current the pump draws depends on how hard it has to work (how high it has to lift the water, flow restrictions, etc) Charging is something like 50-70% efficient depending on a whole range of factors, battery construction and type, etc. Make sure you check the water level often and only fill with distilled water. Check at least weekly to begin with. Get a cheap meter that can measure current up to 20 amps (since there could be a startup current spike) and see what the pump actually uses in your setup. Even a cheap Harbor Freight meter will be good enough for this. |