Monitoring the remaining power of a 12V battery with a PC

[Quixote_1]

Can anyone suggest a way that I would be able to get a readout (perhaps with a 1-wire sensor) of the remaining power as a percentage of an 80Ah marine battery on my computer? I'd like to be able to monitor it using Girder. I plan on expanding the system to an array at some point and I would like to be able to trigger events when the power drops below a certain level.
Thanks for any inspiration!

 

[DavidL]

Can anyone suggest a way that I would be able to get a readout (perhaps with a 1-wire sensor) of the remaining power as a percentage of an 80Ah marine battery on my computer? I'd like to be able to monitor it using Girder. I plan on expanding the system to an array at some point and I would like to be able to trigger events when the power drops below a certain level.
Thanks for any inspiration!

Measuring remaining battery capacity isn't such an easy task. It is easiest when the current draw on the battery is consistent. You can monitor the battery voltage, and monitor that over time until whatever the device connected uses up enough of the capacity to not perform it's job (ie: a light is too dim for usage or a motor stops running at a normal speed).

There are issues of "surface charge" which means the battery doesn't have much capacity, but the voltage is still high.

The voltage should be taken under it's normal load for a more accurate determination. In car lingo, this would be "cranking voltage".

The other issue is that over time a battery looses capacity. Dependent on battery type, this can be caused due to sulfation of the cells. So your percentage indicator would have to compensate for this reality.

You could monitor both voltage AND current for best indication. This would be over time and with some math of the amperage times the voltage (over time), would give a better indication of how much battery is left, if the current draw isn't always consistent.

If the load isn't all the time (like a PC UPS that isn't on charge all the time), then the time sitting between charges depletes the available juice.

Will the battery be charged on a regular basis? Or just after it has been totally depleted? Yet another factor.

 

[Quixote_1]

Thanks so much for the informative post!
The situation is that I have set up a door entry system using iButton readers (iLock boards), which are powered off a deep cycle marine battery. As well, I have the doorstrike on the same battery and my doorbell. I will also be adding 2 electric deadbolts and a linear actuator at some point. I would like to add more batteries in parallel and an inverter for use in power outtages as well as possibly power a bunch of emergency LED lights.
I want to tie this into my automation system (using Girder 5) so that once the batteries reach a certain level I can receive a text message or be alerted when at home through text-to-speech announcements.

It is imperative that the power never dies because then I will never make it back into my home without a battering ram.

 

[JohnWPB]

It is imperative that the power never dies because then I will never make it back into my home without a battering ram.

I personally would never trust automation or battery levels to that extent. I am going to be putting an electric lock on the front door in the next month or so as part of a remodel. I have chosen to use one that also uses a standard key as a "backup".

 

[PaulD]

It is imperative that the power never dies because then I will never make it back into my home without a battering ram.

As insurance, I would run a pair of wires to some accessable location where I could hook up a battery from outside the house so I could provide emergency power externally if I had to. Cheaper than repairs from a battering ram.

 

[Quixote_1]

It is imperative that the power never dies because then I will never make it back into my home without a battering ram.

As insurance, I would run a pair of wires to some accessable location where I could hook up a battery from outside the house so I could provide emergency power externally if I had to. Cheaper than repairs from a battering ram.

Very true. I had considered that some time ago, but totally forgot about that plan. Thanks for the reminder!

 

[Quixote_1]

It is imperative that the power never dies because then I will never make it back into my home without a battering ram.

I personally would never trust automation or battery levels to that extent. I am going to be putting an electric lock on the front door in the next month or so as part of a remodel. I have chosen to use one that also uses a standard key as a "backup".

That's probably a better idea, but I have a bit of a penchant for overkill and that would not be feasible with the system I have planned. I'm installing 2 electric failsecure deadbolts; one at the top of the door and one at the bottom. A linear actuator will be attached to the wall and the door on the hinge side to open and close the door.

 

[SteveQ]

Can anyone suggest a way that I would be able to get a readout (perhaps with a 1-wire sensor) of the remaining power as a percentage of an 80Ah marine battery on my computer? I'd like to be able to monitor it using Girder. I plan on expanding the system to an array at some point and I would like to be able to trigger events when the power drops below a certain level.
Thanks for any inspiration!

Have you considered automating the charging of the battery. Keep a charger connected and turn it on once a week (or whatever) with your girder system.

Steve Q

 

[CollinR]

Failsecure on an exterior door of a residence is about the dumbest thing I have heard in a while. I surely hope this is not whats being discussed. Tell use you have a datacenter or run a 911 dispatch office (the ones I have been in didn't use fail secure) in some rural area. At a minimum research how these systems are normally installed and why, in the real world it's a cold day in hell when a professional installs failsecure bolts in areas where people frequent. At least look at strikes and use normal deadbolts so you can get out quickly if you needs to.