The 150 series Dual Battery Guide

[dBC]

I know that the last time I checked, my D27F will sit on on 13.1v open circuit after 24 hours.

That sounds fully charged to me. Good luck getting it to that level of charge with a 13.4V alternator output.

[120D4D]

Arguments aside about DCDC vs Alternator charging I know that the last time I checked, my D27F will sit on on 13.1v open circuit after 24 hours.

Yes I run a BCDC1220 and yes I know its slower/less than ideal but that just what I have in my set-up, I also almost never have a heavily discharged Aux to start with though...

[dBC]

That might be an interesting experiment mullerwh, if you're up for it. Disconnect the voltmeter so there is zero-load on the battery, drive as normal for a week or so (no diode installed) so that you've got it as charged as you're ever likely to, and then disconnect the battery completely for 24 hours so it's neither being charged or discharged. Then see how close it gets to the 13.1V in the datasheet. My guess is it'll still read about 12.7V.

Those VSRs like to share the discharge for quite a bit after you shutdown, so to really test whether you're getting it fully charged you probably want to isolate it once you get home, leave it isolated for 24 hours and then check the voltage.

[drivesafe]

I found one datasheet that claims the fully-charged open circuit voltage for those should be 13.1V

Hi dBC and open circuit voltage readings are irrelevant in automotive situations, where the battery is still in the vehicle.

For an open circuit voltage reading to be accurate, the battery must be in a No-Load/No-Charge state for at least 24 hours, before you can take the voltage reading.

So short of removing the battery from the vehicle and letting it rest for 24 hours, again, open circuit voltage readings are useless.

[drivesafe]

Hi again mullerwh, as amts posted, at 12.7v, your battery is well and truely fully charged.

The chart below will give you the SoC for any lead acid battery, while it’s in a vehicle.

[dBC]

If 12.7V is at rest, then it is pretty much 100%.

I found one datasheet that claims the fully-charged open circuit voltage for those should be 13.1V (http://www.federalbatteries.com.au/f..._YellowTop.pdf). But I guess it's possible that the small current drawn by mullerwh's voltmeter is dragging it down a little. mullerwh, do you get different results if you leave your voltmeter disconnected for a week or so, and then check it?

If it's never getting more than about 13.6V it may be that the cells have become unequal. A higher voltage charge will let you push past the cells that are full and get some charge into the ones that aren't (aka boost stage, or equalisation stage). The easiest solution might be to just put your diode back in. What does the yellow top read after a few weeks of running with the diode?

If 12.7V is at rest, then it is pretty much 100%.
Charging at 14.6V is quite normal and not an issue https://www.optimabatteries.com/en-u.../charging-tips

My 120 V6 alternator is at 14.4V when driving.

[mullerwh]

Thanks for the reponse drivesafe. The reason why I'm looking at replacing the isolator is because it seems the Optima yellowtop battery is never fully charged. I rarely use the battery, I only run a fridge of it every few months but drive the vehicle on daily basis for about 30-40 minutes x 2 trips but the battery remains on 12.7v. I'm still trying to confirm if 12.7 is considered to be full. Another thing is the redtop stays 12.6v. I know the projecta has cut out of 12.8v. I'm running a voltage meter in the car onnected to both batteries and during winter time the alternator (without the fuse modification) sits at 13.6 / 13.7v when the engine is running and in my opinion this is sufficient for charging. I do have the fuse from leight but found during winter time that it pushes the voltage to 14.6 which I'm not totally comfortable with.

[drivesafe]

Hi mullerwh, and mate, using a DC /DC device, even a 40 amp one, will actually take longer to recharge an low Optima than what your alternator can do.

In your case, with a 25 amp DC/DC device, you will actually take more than twice as long to recharge your D34 Optima if it is low.

Just leave your isolator in place, it will do a much better job.

[mullerwh]

I went with with redtop D34 as a cracking battery...supposedly better for cranking. I run a yellowtop D34 as 2nd battery with an project isolator. Installed 2 years ago and no issues. Will be removing the isolator shortly and installing BCDC1225...just because I have spare as a left over from my trailer

When winching, the engine needs to be on, so the SBI12 is already linked.

[Scott13april]

optima D34 as cranking battery

I’m looking to replace the cranking battery in my 2010 prado 150.

The car has a dual battery system with an aux optima D34 connected via a Redarc Sb12.
It has lots of accessories including spotlights and warn winch.

I initially removed the N70ZZL (24kg) cranking battery that the car came with, due to finding a crack under the fuse box, and chucked in an old lighter battery (18kg) I had in the shed.

I’d like to get a good battery as have a Tassie trip coming up, and experienced a flat cranking over weekend.

I’ve been considering a D34 Yellow on the assumption that I can get decent CCA of 750 and when required join them via the Redarc Sb12 when winching via switch on dashboard.
Alternatively the D27 gives higher RC values for winching but also has a higher weight that I’d like to avoid.

What do you guys thing of my dual D34 idea, linked via Sb12 when winching?

Should be fine then.

[KeenOnFishing]

Yes, Mainly when it is parked up after a trip to ensure aux gets a full charge

When will you plug in the charger? When the engine is stopped?