Zero Sum vs. Sliding Window Charging

[Dockhead]

I think even the question is rooted in lead thinking.


With lithium, you just don't even think about it. A lithium battery bank is like a fuel tank -- it doesn't care whether it's 1/3 or 2/3 full. All you have to do is watch the level and be sure you're not getting too low. That's all there is to it.


If you start to run out, you just fire up another charge source. Simples.



I am really looking forward to enjoying this aspect of lithium power.

[Stu Jackson]

Originally Posted by evm1024

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But to actually use sliding window to its advantage we need to change our mindset and slid the window by design with an increase the total house bank capacity to cover more than 2x daily usage. 5x to 10x being the ballpark size.

Food for thought….

Not really. To me all that you've presented are two different "cute" names for sizing a house bank. Doesn't matter what the charge source is. Some things just never change... Do an energy budget. Get the biggest house bank you can. Period.

[evm1024]

Originally Posted by Dockhead

I think even the question is rooted in lead thinking.


With lithium, you just don't even think about it. A lithium battery bank is like a fuel tank -- it doesn't care whether it's 1/3 or 2/3 full. All you have to do is watch the level and be sure you're not getting too low. That's all there is to it.


If you start to run out, you just fire up another charge source. Simples.



I am really looking forward to enjoying this aspect of lithium power.

Lithium does change the game - Zero sum and Lithium do not mix well. But, thrive on sliding windows.

The fuel tank is a classic case of total loss system. Run until it gets so low that you must fill it up. Only when I was in school did I only put a few gallons in (too poor to fill it up) - sliding window. And I never filled it after each use (zero sum).

[evm1024]

Originally Posted by Stu Jackson

Not really. To me all that you've presented are two different "cute" names for sizing a house bank. Doesn't matter what the charge source is. Some things just never change... Do an energy budget. Get the biggest house bank you can. Period.

I like the idea of the biggest energy storage I can get.

I currently have a 317989 AH in my largest "bank". At 12.8 volts that is 4070 KWH.

I use that bank in total loss mode typically. I recharge it every now and then.

I like cute names but these names are in common use in other domains and appear to apply here too.

Total loss is common in race cars for example.

[evm1024]

Of course that is the energy in 100 gallons of diesel.

[valhalla360]

Originally Posted by evm1024

My reason for posting was not to address how our battery systems end up operating in the real world. I was pointing out that in the design/sizing phase we can set the parameters with a specific mode in mind. And that there are advantages to doing so.

There are many examples on my boat where I have battery systems operating by design in zero sum or total loss modes.

As an example a start battery is operated in zero sum. My rechargable
VHF radio is operated in zero sum. Keep them fully charged, use it and then recharge to full. My cell phone too.

Flashlights as an example and cordless power tools are total loss systems. Use them till they stop working and then recharge (or replace) the battery.

I was pointing out not how a battery system was operated in practice but
rather what mode the system was designed to operate in. And more
specifically designing to a specific mode can cause suttle changes in

Actually even your examples aren't specifically designed for zero sum...it just happens to work out that way most cycles. Just like the vast majority of cruising boats live at dock so they function in a zero sum mode, but it's by coincidence more than by design.

Even car batteries...if you are doing deliveries where you start and stop the engine every couple minutes, it may not get fully charged before being turned off but as long as it's not way low, it's not an issue.

Rechargeable tools...I often wind up giving them a short charge to get enough juice to finish a job. That would technically fall into sliding window.

I don't think the whole idea that someone designs around zero sum is false. They design around how often do you need an outside charging source...for some (like a car starting battery), the assumption is almost never. For others, it may be quite frequent.