expired Posted by TWrudy1978 • Jul 18, 2020
Jul 18, 2020 4:23 PM
Item 1 of 1
expired Posted by TWrudy1978 • Jul 18, 2020
Jul 18, 2020 4:23 PM
Interstate DCM0035 12V 35AH Sealed Lead Acid AGM Deep Cycle Battery
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Deep cycle batteries are distinctive from starting/ignition batteries in their intended use, and therefore their design to support that use.
Design differs primarily in the construction of their lead plates. Starting batteries have thin or cellular (think sponge) construction to maximize surface area; this maximizes the current produced, but it also deteriorates quicker if discharged significantly. Deep cycle batteries have fewer, thicker/solid plates, involving far less surface area and therefore the current they can produce is lower, but they withstand higher discharge much better.
So, for example, a starting battery may be intended to provide, say, 400A for 15 seconds, and likely will be recharged before it supports another start. Each "cycle" may only be 2% or 3% discharge. The plates are designed around this use case.
Deep cycle, in contrast, is intened to provide much lower currents for much longer durations. For a common 115Ah AGM in an RV application, they may support a 4A or 5A discharge for 10 hours before being charged again.
Better battery suppliers provide a set of discharge curves in datasheets which quantify this behavior. Interstate, not surpisingly, does not provide these. In fact, this DCM0035 battery can't even be found on their website as far as I can tell.
So we are left to generalize. And the 50% figures being noted by others are accurate.
50% is a widely followed rule of thumb for system designs with sealed lead acid batteries. If your application typically needs to support X amp hours of load between charges, the design should use a battery of 2X or more amp hour capacity. The rationale behind this is economy: balancing the upfront cost of the battery against the cumulative power provided over its life. This relationship isn't linear; a battery which supports 2000 cycles at 40% discharge may only support 700 cycles at 80% discharge (notably less than 1000 cycles that a linear/proportional curve would imply). And while the curves vary among specific batteries, the "sweet spot" is typically near 50%. This assumes that the battery is a true deep cycle design (ie, fewer, thicker plates). Many cheaper batteries marketed as deep cycle (and this DCM0035 seems an example of such) are often not a pure deep cycle design, and in those cases the sweet spot for maximum % discharge actually reduces to less than 50%.
There are other considerations which further support the 50% guidance.
One example: Designing a system to 80% discharge leave far less margin for atypical discharge events. In other words, if your system is regularly going to 80% discharge, it won't take much of an anomaly in the load (a motor running 5 hours rather than 4? a fan running 10 hours rather than 8?) to run into 90-95% discharge territory, and that can rapidly deteriorate (or "damage") a sealed lead acid battery.
Another example: voltage levels. The voltage on these batteries drop as they discharge. At 80% discharge, the voltage level can easily drop enough to be insufficient for voltage sensitive loads. In some cases, sustained sub-spec voltage supply could damage a device. Designing a system to 50% discharge has far less vulnerability to these issues.
@Kman, you are correct that deep cycle sealed lead acid batteries CAN be discharged beyond 50%. And its probably also fair to say that occasional (say, one in 10 cycles) discharges to 80% will not dramatically impact the battery life. But you've gone well beyond that position, and essentially dismissed the 50% rule of thumb as unfactual BS that should be ignored. That's where you're wrong. The 50% discharge guidance is well justified by the engineering data, and that's why its been a widely accepted rule of thumb for decades.
i keep killing my car battery because of the always on cigarette lighter socket.
i have my dashcam plugged it and sometimes forget to unplug it.
after doing that a few times, the battery no longer holds enough charge for me to start my car.
have replaced the battery twice in my 4year old car.
are there any deep charge car batteries? (yeah, alternatively, i can get rid of the dash cam.)
Or you can put a deep cycle battery in your trunk just for your dash cam on parking mode.
No, too small and the wrong type. These are meant to power electric devices continuously and be able to be drained without being damaged, unlike car batteries.
They appear to be precisely the kind you'd use with a small panel, charge controller and inverter, like for an attic or cabin.
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Your assertion -- that deep cycle batteries obviously are intended to discharge way past 50% because the word "deep" is involved -- is simplistic at best, and wrong at worst.
Deep cycle batteries are distinctive from starting/ignition batteries in their intended use, and therefore their design to support that use.
Design differs primarily in the construction of their lead plates. Starting batteries have thin or cellular (think sponge) construction to maximize surface area; this maximizes the current produced, but it also deteriorates quicker if discharged significantly. Deep cycle batteries have fewer, thicker/solid plates, involving far less surface area and therefore the current they can produce is lower, but they withstand higher discharge much better.
So, for example, a starting battery may be intended to provide, say, 400A for 15 seconds, and likely will be recharged before it supports another start. Each "cycle" may only be 2% or 3% discharge. The plates are designed around this use case.
Deep cycle, in contrast, is intened to provide much lower currents for much longer durations. For a common 115Ah AGM in an RV application, they may support a 4A or 5A discharge for 10 hours before being charged again.
Better battery suppliers provide a set of discharge curves in datasheets which quantify this behavior. Interstate, not surpisingly, does not provide these. In fact, this DCM0035 battery can't even be found on their website as far as I can tell.
So we are left to generalize. And the 50% figures being noted by others are accurate.
50% is a widely followed rule of thumb for system designs with sealed lead acid batteries. If your application typically needs to support X amp hours of load between charges, the design should use a battery of 2X or more amp hour capacity. The rationale behind this is economy: balancing the upfront cost of the battery against the cumulative power provided over its life. This relationship isn't linear; a battery which supports 2000 cycles at 40% discharge may only support 700 cycles at 80% discharge (notably less than 1000 cycles that a linear/proportional curve would imply). And while the curves vary among specific batteries, the "sweet spot" is typically near 50%. This assumes that the battery is a true deep cycle design (ie, fewer, thicker plates). Many cheaper batteries marketed as deep cycle (and this DCM0035 seems an example of such) are often not a pure deep cycle design, and in those cases the sweet spot for maximum % discharge actually reduces to less than 50%.
There are other considerations which further support the 50% guidance.
One example: Designing a system to 80% discharge leave far less margin for atypical discharge events. In other words, if your system is regularly going to 80% discharge, it won't take much of an anomaly in the load (a motor running 5 hours rather than 4? a fan running 10 hours rather than 8?) to run into 90-95% discharge territory, and that can rapidly deteriorate (or "damage") a sealed lead acid battery.
Another example: voltage levels. The voltage on these batteries drop as they discharge. At 80% discharge, the voltage level can easily drop enough to be insufficient for voltage sensitive loads. In some cases, sustained sub-spec voltage supply could damage a device. Designing a system to 50% discharge has far less vulnerability to these issues.
@Kman, you are correct that deep cycle sealed lead acid batteries CAN be discharged beyond 50%. And its probably also fair to say that occasional (say, one in 10 cycles) discharges to 80% will not dramatically impact the battery life. But you've gone well beyond that position, and essentially dismissed the 50% rule of thumb as unfactual BS that should be ignored. That's where you're wrong. The 50% discharge guidance is well justified by the engineering data, and that's why its been a widely accepted rule of thumb for decades.
And, I never said that there wasn't a cost in going much under 50% on a regular basis. I acknowledged that. I just said that one, the additional power obtained partly made up for the shorter battery life, and two, most people are probably going to want to use more than 50% than spend more on extra capacity up-front, even if they have to replace batteries more often and pay more over time. You're trying to apply commercial metrics and standards on non-commercial installations.
Also, the figures I came across said that going to 80% instead of 50% regularly approximately halves the battery life, which is way less than the 2000/700 hour figure you cited. And I know the difference between deep and non-deep cycle, in construction and use, and that we're talking about deep cycle here.
And 20 minutes was more than enough time to figure out all of this. I'm not disputing anything that you said, just saying that it won't matter to most people. Same as how most people charge their phones to 100% and then use them till they're almost empty, which is bad for battery life but how human nature works.
Finally, with everything gradually moving to lithium, and energy-saving devices gradually replacing energy hogs, this will all become moot fairly soon, in 5-15 years. Mass-produced EV replacements for ICE-powered ones aren't feasible without lithium, and electric planes are inconceivable without them, and these numbers have no meaning there.
Or, this one for $63 [amazon.com]
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You need deep cycle batteries for that application so these would definitely work. With only 35Ah however I think your monty would be better invested into a higher capacity battery. For example, you can get a single 100Ah battery for less than three of these, which is what you would need for the same capacity. You'll be taking up at least double the space and buying much more wire when compared to the 100Ah batteries, not to mention wasting money as well.
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