Cut Off Voltage for 12V Hybrid

[TonyM]

I drive a hybrid car with a small 45Ah 12V battery. I'm trying to decide between hardwiring to the car battery, or to a dashcam battery.

I have done some discharge tests on my PowerCore 6200LFP battery and I'm getting a usable capacity of 60Wh. I am planning to do some discharge tests on my car 12V battery for comparison.

What is the recommended cutoff voltage to set on the hardwire kit to ensure good health of the 12V battery? Can I go down to 11.6-11.8V, or should I stay high at 12.4-12.5V?

 

[kamkar]

I think 12.2 volts are generally seen as a 50 % depleted lead acid battery, and should be safe in regard to too low discharge, it is what i have always used ( also 45 Ah battery but upgraded to 50 Ah one a few years ago )

 

[Nigel]

Depends on the chemistry of the 12V battery, and on if it is recharged from the traction battery.

Some hybrids use conventional lead acid, which wants a 12.2V cutoff, as kamkar suggests.
Some use AGM batteries, because of longer life time, and less self-discharge, which is important for a small battery, and that wants 11.8V cutoff. If you have a conventional lead acid, then you may be able to replace it with an AGM for better performance and faster recharge.
Some newer models use lithium 12V batteries, which is probably best with 11.8V, although 11.6V won't do any damage, just means that you can't leave the car unused for weeks because there wont be much left for the alarm system etc.

I don't think many charge the 12V from the traction battery while parked, unlike many EVs, but they will charge it from the traction battery while driving, even if stopped at the lights with the engine stopped, so you should get a decent recharge on every drive.

 

[TonyM]

Depends on the chemistry of the 12V battery, and on if it is recharged from the traction battery.

Some hybrids use conventional lead acid, which wants a 12.2V cutoff, as kamkar suggests.
Some use AGM batteries, because of longer life time, and less self-discharge, which is important for a small battery, and that wants 11.8V cutoff. If you have a conventional lead acid, then you may be able to replace it with an AGM for better performance and faster recharge.
Some newer models use lithium 12V batteries, which is probably best with 11.8V, although 11.6V won't do any damage, just means that you can't leave the car unused for weeks because there wont be much left for the alarm system etc.

I don't think many charge the 12V from the traction battery while parked, unlike many EVs, but they will charge it from the traction battery while driving, even if stopped at the lights with the engine stopped, so you should get a decent recharge on every drive.

Thanks for the advice. Looks like lead acid, so 12.2V then.

It is not recharged from the traction battery when parked, but it is recharged if the ignition is on.

 

[Nigel]

Yes, if you are going to leave it unused for a week or two then it may be semsible to set it a bit higher, or turn the camera off.

I think you could quite easily find an AGM replacement in the same size, which would charge faster, and be happy with a deeper discharge to 11.8V , and have probably double the life span.

 

[TonyM]

Yes, if you are going to leave it unused for a week or two then it may be semsible to set it a bit higher, or turn the camera off.

I think you could quite easily find an AGM replacement in the same size, which would charge faster, and be happy with a deeper discharge to 11.8V , and have probably double the life span.

I'll see how much recording time I get from the 12V battery. I may end up using my powercore dashcam battery instead.

 

[Nigel]

I'll see how much recording time I get from the 12V battery. I may end up using my powercore dashcam battery instead.

I think your most likely problem is that the battery will not charge fast enough, since your journeys are quite short. AGM batteries do charge faster, and don't need taking into the house for charging. Of course they still have limits!

 

[TonyM]

I think your most likely problem is that the battery will not charge fast enough, since your journeys are quite short. AGM batteries do charge faster, and don't need taking into the house for charging. Of course they still have limits!

That's why I'm testing so I can make a plan, to see if I can get either the car battery or dashcam battery to work on a cycle of 30min drive / 9 hour parked. Should be no problem if I buy an A329S and go with LPID mode.

At the moment I'm getting by with a power station that I bring inside to charge once a week. It barely charges from the 12v socket whilst driving.

 

[kamkar]

I have only used timed parking guard when i used the car battery, so not able to give any hints as to expected time you can expect.

 

[TonyM]

I have only used timed parking guard when i used the car battery, so not able to give any hints as to expected time you can expect.

That's OK, that's why I'm going to test it. Idle the car until the battery is charged, then leave it parked until the hardwire kit turns off at 12.2V.

 

[Michael23]

Hello Tony,
[Just posting from an old electricians point of view.]
May I suggest that you take a few moments to read the "YUASA" article & note the section on...
> "When is a conventional battery best?"
& this item in particular... > Please also note that a conventional battery cannot simply be replaced with an AGM battery. If your vehicle originally had a conventional battery, the vehicle rectifier or regulator design is for a conventional battery, and it could cause an issue with the replaced AGM battery. The opposite way as well.

I haven't seen any other sites that mention this item, but I haven't checked them all.

The experts on this fora may have more information on the subject.

YUASA site > https://www.yuasabatteries.com/resources/guides/agm-battery/

Oh, btw, may I suggest that you do not just idle the car till the battery is charged, instead, go for a drive as it's much more efficient & you will enjoy the country side....😎

 

[TonyM]

Hello Tony,
[Just posting from an old electricians point of view.]
May I suggest that you take a few moments to read the "YUASA" article & note the section on...
> "When is a conventional battery best?"
& this item in particular... > Please also note that a conventional battery cannot simply be replaced with an AGM battery. If your vehicle originally had a conventional battery, the vehicle rectifier or regulator design is for a conventional battery, and it could cause an issue with the replaced AGM battery. The opposite way as well.

I haven't seen any other sites that mention this item, but I haven't checked them all.

The experts on this fora may have more information on the subject.

YUASA site > https://www.yuasabatteries.com/resources/guides/agm-battery/

Oh, btw, may I suggest that you do not just idle the car till the battery is charged, instead, go for a drive as it's much more efficient & you will enjoy the country side....😎

Thanks for the link. I had no intention of replacing the battery.

Regarding the comment about idling, I was only thinking about about 30 seconds or so after parking on the driveway. Sometimes the car's BMS keeps the engine running for a short duration whilst I'm stationary to top up the battery. This might only be for the traction battery, but it might also be topping up the 12V battery too - I'm not sure.

 

[EricSan]

Oh, btw, may I suggest that you do not just idle the car till the battery is charged, instead, go for a drive as it's much more efficient

I recall reading something a little while ago that most alternators don't "really" charge the battery until they hit a certain RPM level (typically above idle), so idling may not accomplish very much charging at all. I suspect this is subject to the usual caveats of variations by car make and model and differences in electrical design.

I also agree that swapping battery chemistries is not a great idea. Different chemistries have very different charging patterns and voltage/current characteristics that vary over the duration of the charge cycle, and especially at the end of the charging cycle.

 

[TonyM]

OK, so no idling then. I suppose it makes more sense to test the battery capacity directly after a drive to or from work, since that is when I would be using the 12V battery to power the dashcam in parking mode.

 

[DashGuard]

I recall reading something a little while ago that most alternators don't "really" charge the battery until they hit a certain RPM level (typically above idle), so idling may not accomplish very much charging at all. I suspect this is subject to the usual caveats of variations by car make and model and differences in electrical design.

I also agree that swapping battery chemistries is not a great idea. Different chemistries have very different charging patterns and voltage/current characteristics that vary over the duration of the charge cycle, and especially at the end of the charging cycle.

Charge rate is lower at idle. As you mentioned there are many variables to the way the alternator works depending on the vehicle, some don't load the alternator once the battery controller deems it at sufficient charge.

OK, so no idling then. I suppose it makes more sense to test the battery capacity directly after a drive to or from work, since that is when I would be using the 12V battery to power the dashcam in parking mode.

12.4V is too high to set as cut off. Brand new batteries hang around 12.55-6v when 100% charged, so you're not going to get a 9hr park mode out of that.

In the summer time, you can get your car started at 11.6V, not winter. I would feel safer at 12.2v in the winter, depending on how low the temps drop. I personally run my cams straight off the car battery all year round, only -25-30c dips turn them off. Although I can do this because I drive my cars at least 45minutes 2x per day and when my batteries have been replaced with highest capacity possible. I would consider learning about your hybrid mode for your vehicle, does it need engine battery to switch to engine from hybrid? does it run all electronics primarily on engine battery? Ultimately you're running down your engine battery by using it for park mode and making it less reliable.