Battery monitor setting for parallel batts

[Hiyu]

Hello All,

I just installed a Renogy Battery Monitor on my rig. I have two wet cell batteries in parallel rated at 160 RC ea. I set my monitor to 160 RC when calibrating it. Should I leave it like this, or should it be set to 320 RC?

As always, thank you in advance,

Don

[rossvtaylor]

Hi Don, I think you'll need to check with Renogy on this. RC is a rather unusual measure to use when talking about deep-cycle use, because the result of using the entire reserve capacity would take your batteries down to 10.5 volts or so...much lower than you'd want to take a deep-cycle battery. If you used the entire 160 minutes of 25A draw, that's a bit over 65Ah for each battery. But you don't want to take then down that far. Taking your batteries down to 10.5 volts on a regular basis will damage them, especially since it sounds a bit like these aren't deep-cycle batteries.

Can you share more info on the batteries you're using so we can look up the specs?

[Hiyu]

Hi Ross,

Thanks for the input. You're correct on the Ah rating per battery, double that, I have 130 Ah, so I'm deducing that I enter that number in the Renogy first field. I contacted Renogy and am awaiting their response for verification. Regarding deep cycle batts, I thought they were designed to be taken down to a much lower value that car batteries without damage. I don't plan on ever getting low on these as they are on a batt maintainer and when we camp, it'll be solar charged or shore power charged. Thanks again, will post what Renogy says. PS: love their battery monitor, what a great asset to have!!

[rossvtaylor]

Originally Posted by Hiyu

Hi Ross,

Thanks for the input. You're correct on the Ah rating per battery, double that, I have 130 Ah...

I did mention 65Ah per battery using the RC rating...but don't forget the following sentence, that you don't want to take your batteries down that far. 10.5 volts is WAY too low and would be damaging to the batteries. Sulfation will be occurring well before that. Generally, I think, deep cycle batteries are considered 1/2 discharged at about 12.2 volts...but voltage is not a perfect measure of SOC because other factors impact that too.

So, the reason I asked for specifics on your batteries was to help determine their actual Ah rating and your usable capacity. I suspect you have considerably less capacity than the 130Ah you're figuring, because that would take your batteries down to under 11 volts (using the normal RC rating).

Can you share the battery brand and model?

[Hiyu]

Here's the spec's, thanks for the help

[rossvtaylor]

Hi Don. It took some doing, but I found the specs on that battery and unfortunately it's not a deep-cycle battery. I became suspicious when you mentioned the RC rating, because that is not commonly used with true deep-cycle batteries. And in general, any battery with a CCA rating is not a true deep-cycle battery.

I have had pretty good luck with the Duracell "marine deep cycle" batteries I've used before. They are 100Ah rated (so, 50Ah usable) and held up for years. They would be a good budget/value battery for someone and I do recommend those (or similar) for some folks.

But that Interstate battery has labeling that I would describe as possibly misleading to buyers. I would think that a battery with "RV/Marine" labeling would be a deep-cycle "light" battery. Not a true deep-cycle, like a golf cart or L16 off-grid battery...but at least usable. But that Interstate battery is a specialized RV/Marine starting battery. It's a regular starting battery that's designed to be a bit more rugged and tolerant of vibration, apparently.

If these batteries work for you and give you what you need, then right on. Everyone has different needs and goals and plans. But don't expect that these will behave like deep-cycle batteries. Think of them more like car starting batteries. Having said that, and trying to answer your original question, if I were to guess at a starting value for your monitor setting I would set it for about 60Ah total (for the bank of 2 batteries). I would then watch things and see how many Ah you've used before the bank drops to 12.2 volts, which would be a good ballpark value for 50% discharged. If you want to really know, you could hook up a load and a timer and test it.

I hope this helps somewhat.

[Hiyu]

Thanks Ross, I had a hunch they may be a hybrid....

So far they're doing the job this past year, when they can't do the job, I'll upgrade. I'll set the parameter as you suggested, best to err on the safe side.

Thanks again.!!

[rossvtaylor]

Agreed...better to not draw too low and be cautious until you get more data. I do love lithium technology and it's getting more and more affordable. But there's something to be said for a low-investment setup to get started...and maybe last for years...while you test and learn and grow. Be well. It seems like you have a great attitude about all this!

[Hiyu]

Another question/thought. When entering the Ah, you're setting the parameter that the monitor will project how much poop is in the tank so to speak.

That said, when you monitor the battery voltage, that gives you real time of the battery, and if you set your alarm at a desginated low voltage setting, it will alarm at said low voltage.

Now... if you enter an incorrect Ah value, your voltage alarm will still let you know when you've reached a state that needs tending to...

Am I understanding this correctly?

Thanks in advance again

[rossvtaylor]

That sounds right...just set the alarms where you want them. An incorrect Ah rating will only impact the % capacity graph, and it may not even affect that if the monitor bases the charge state with voltage...which is common. I don't know how that particular monitor is set up, but in any configuration the voltage alarms are the important bits.

[Hiyu]

Thanks for the confirmation....