1st Battery Capacity complete

[Pass me]

My battery is ~ 5 yrs old. It is a 12V Interstate Powerfast PF 27DC - 7.
I ran it down to ~10.5V using an inverter w a 60W bulb, it took ~ 15 hrs.
I was aiming for 20 hrs of course so if my math is right I'm dealing with a 70Ah battery. As suggested I'm now charging r up and will run a 2nd test.

 

[Domo]

Sounds like this is a continuation of another thread...?

I have to ask why you are testing it? The poor thing is 5 years old. If you want reliability when on the road I'd strongly suggest you bring it to your local auto store to have a load test and verdict - rather than bring it to the dead-zone of 10.5 volts repeatedly at home.

Having said that, IF the battery has been maintained well and not abused you could get a couple more years.

I'd bring it to a car store and have it load tested, which could give you a easier decision point.

 

[Pass me]

That's what I will do at the end of this project just to see how things stack up. I am doing this to better understand the dynamics of a LAB if you will. Folks have been great!
Being brand new to the forum I've been messing around with how to reply, trying to simplify things really.
The suggestion to return to my original post was how I ended up responding in two posts......I think! Lol.

 

[Mark_K5LXP]

Ah, there's an RC spec on that label and that more directly correlates to Ah. 160RC is 66.7Ah (25 amps for 160 minutes). A 60W bulb is 5A at 12V (plus some warming the inverter) so a bit heavy for a 67 Ah C/20 test. WIthout factoring for peukert (working that backwards through the RC spec to C/20 Ah), 15 hours at ~5A is 75Ah so your battery is right up there. A 2nd test (I would run another equalize) will show if it gets any better but first pass I'd say is looking pretty good. Generally by the time folks report their batteries are sickly the horse has already left the barn. If it's working this well at age 5 I'd say at a minimum it was treated right.

Mark B.
Albuquerque, NM

 

[Pass me]

Wow, great news but a little disappointing that my base info is out to lunch. Google told me: CCA÷7.25=Ah and I've been running with 93 Ah ever since. I will research how to use RC to determine Ah.
The attached is the info Interstate supplied, they didn't answer when asked the battery Ah info if memory serves.
I am recharging now and will for sure run another equalize. Can this be done back to back to verify maximum battery voltage has been reached?
The 2nd capacity test will be dialed down to the recommended draw 13% of Ah) = 8-9A. Aiming for 20 hrs and it sounds the odds are pretty good.

 

[Tulecreeper]

Wow, great news but a little disappointing that my base info is out to lunch. Google told me: CCA÷7.25=Ah and I've been running with 93 Ah ever since. I will research how to use RC to determine Ah.
View attachment 169993

RC to Ah - there are two (2) methods, both of which give the same answer but one is much simpler:

The simple method:

RC x 0.417 = Ah - So, 160(RC) x 0.417 = ~67

or the more complex method:

RC/60 = XX =====> XX x 25 = Ah - so, 160(RC)/60 = 2.66 =====> 2.66 x 25 = ~67

 

[Mark_K5LXP]

Google told me: CCA÷7.25=Ah

CCA is a merit of instantaneous current delivery, not energy storage. It's just an approximation.

I will research how to use RC to determine Ah.

RC/60*25. Now, to split hairs, this is the Ah at 25A draw which is a nominal 7x of what the approximate C/20 rate is for this battery. You only have one discharge rate now (~5A) so can't calculate peukert but a WAG to your C/20 Ah rating is probably closer to 75Ah than 67. But, the fact you got almost all of that strongly implies a healthy battery.

they didn't answer when asked the battery Ah info if memory serves.

I've gotten product info from interstate using their web contact page. The one I have handy is for a group 24 marine and it shows 64Ah for RC140, so the numbers we're seeing for your group 27 seem to line up. For the group 24 the RC Ah is 58, C/20 rate is 64, 10% difference. On yours the RC Ah is 67, +10% for C/20 would be 74 Ah. Again, none of this is precision and I would consider any result >80% to be "pass". For extra credit you can monitor cell temperature and apply a correction factor for that but for this kind of testing precision isn't usually necessary.

I am recharging now and will for sure run another equalize. Can this be done back to back to verify maximum battery voltage has been reached?

A complete charge cycle will finish the bulk phase and run the entire absorb phase time (4 hours typical) before it would switch to float/complete. Then you can run an equalize charge.

With a couple of data points now you can track to see how the battery performs at any point in the future. What I do is twice a year, winterize and unwinterize I do a full capacity test and put it in my maintenance log. That way I know what shape the battery is in before I start the camping season, then what trauma I've inflicted during the season when I store it. If you take notes as to specific times and terminal voltages during the course of the test you can do interim abbreviated tests (say down to 12.0V) and see how closely the elapsed time lines up to the last test. Probably overkill for the most part unless you're cycling the hell out of your batteries.

The 2nd capacity test will be dialed down to the recommended draw 13% of Ah) = 8-9A.

You lost me on this one.

Mark B.
Albuquerque, NM

 

[Ray-IN]

Contrary to commonly accepted advice, depleting a re-chargable DC battery does not damage it; the total number of expected cycles for that brand/type battery is reduced. Of course the deeper the discharge %, the more the life-cycles are shortened.

As to back-to-back equalizing charges, IMO this WILL shorten the life-cycles of a battery, as it over-charges the battery intentionally @ 15.5+VDC. This can create enough internal heat to warp the lead plates.
Any battery that lists CCA is not, IMO a true deep-cycle battery.

 

[Mark_K5LXP]

A spec equalize charge is time and current limited, and are generally recommended every four to six weeks for batteries in service. The amount of excess energy put into the battery amounts to some dissolved water, no chance of overheating and "warped plates".

Mark B.
Albuquerque, NM

 

[Pass me]

Google told me: CCA÷7.25=Ah

CCA is a merit of instantaneous current delivery, not energy storage. It's just an approximation.

I will research how to use RC to determine Ah.

RC/60*25. Now, to split hairs, this is the Ah at 25A draw which is a nominal 7x of what the approximate C/20 rate is for this battery. You only have one discharge rate now (~5A) so can't calculate peukert but a WAG to your C/20 Ah rating is probably closer to 75Ah than 67. But, the fact you got almost all of that strongly implies a healthy battery.

they didn't answer when asked the battery Ah info if memory serves.

I've gotten product info from interstate using their web contact page. The one I have handy is for a group 24 marine and it shows 64Ah for RC140, so the numbers we're seeing for your group 27 seem to line up. For the group 24 the RC Ah is 58, C/20 rate is 64, 10% difference. On yours the RC Ah is 67, +10% for C/20 would be 74 Ah. Again, none of this is precision and I would consider any result >80% to be "pass". For extra credit you can monitor cell temperature and apply a correction factor for that but for this kind of testing precision isn't usually necessary.

I am recharging now and will for sure run another equalize. Can this be done back to back to verify maximum battery voltage has been reached?

A complete charge cycle will finish the bulk phase and run the entire absorb phase time (4 hours typical) before it would switch to float/complete. Then you can run an equalize charge.

With a couple of data points now you can track to see how the battery performs at any point in the future. What I do is twice a year, winterize and unwinterize I do a full capacity test and put it in my maintenance log. That way I know what shape the battery is in before I start the camping season, then what trauma I've inflicted during the season when I store it. If you take notes as to specific times and terminal voltages during the course of the test you can do interim abbreviated tests (say down to 12.0V) and see how closely the elapsed time lines up to the last test. Probably overkill for the most part unless you're cycling the hell out of your batteries.

The 2nd capacity test will be dialed down to the recommended draw 13% of Ah) = 8-9A.

You lost me on this one.

Mark B.
Albuquerque, NM

Google told me: CCA÷7.25=Ah

CCA is a merit of instantaneous current delivery, not energy storage. It's just an approximation.

I will research how to use RC to determine Ah.

RC/60*25. Now, to split hairs, this is the Ah at 25A draw which is a nominal 7x of what the approximate C/20 rate is for this battery. You only have one discharge rate now (~5A) so can't calculate peukert but a WAG to your C/20 Ah rating is probably closer to 75Ah than 67. But, the fact you got almost all of that strongly implies a healthy battery.

they didn't answer when asked the battery Ah info if memory serves.

I've gotten product info from interstate using their web contact page. The one I have handy is for a group 24 marine and it shows 64Ah for RC140, so the numbers we're seeing for your group 27 seem to line up. For the group 24 the RC Ah is 58, C/20 rate is 64, 10% difference. On yours the RC Ah is 67, +10% for C/20 would be 74 Ah. Again, none of this is precision and I would consider any result >80% to be "pass". For extra credit you can monitor cell temperature and apply a correction factor for that but for this kind of testing precision isn't usually necessary.

I am recharging now and will for sure run another equalize. Can this be done back to back to verify maximum battery voltage has been reached?

A complete charge cycle will finish the bulk phase and run the entire absorb phase time (4 hours typical) before it would switch to float/complete. Then you can run an equalize charge.

With a couple of data points now you can track to see how the battery performs at any point in the future. What I do is twice a year, winterize and unwinterize I do a full capacity test and put it in my maintenance log. That way I know what shape the battery is in before I start the camping season, then what trauma I've inflicted during the season when I store it. If you take notes as to specific times and terminal voltages during the course of the test you can do interim abbreviated tests (say down to 12.0V) and see how closely the elapsed time lines up to the last test. Probably overkill for the most part unless you're cycling the hell out of your batteries.

The 2nd capacity test will be dialed down to the recommended draw 13% of Ah) = 8-9A.

You lost me on this one.

Mark B.
Albuquerque, NM

Google told me: CCA÷7.25=Ah

CCA is a merit of instantaneous current delivery, not energy storage. It's just an approximation.

I will research how to use RC to determine Ah.

RC/60*25. Now, to split hairs, this is the Ah at 25A draw which is a nominal 7x of what the approximate C/20 rate is for this battery. You only have one discharge rate now (~5A) so can't calculate peukert but a WAG to your C/20 Ah rating is probably closer to 75Ah than 67. But, the fact you got almost all of that strongly implies a healthy battery.

they didn't answer when asked the battery Ah info if memory serves.

I've gotten product info from interstate using their web contact page. The one I have handy is for a group 24 marine and it shows 64Ah for RC140, so the numbers we're seeing for your group 27 seem to line up. For the group 24 the RC Ah is 58, C/20 rate is 64, 10% difference. On yours the RC Ah is 67, +10% for C/20 would be 74 Ah. Again, none of this is precision and I would consider any result >80% to be "pass". For extra credit you can monitor cell temperature and apply a correction factor for that but for this kind of testing precision isn't usually necessary.

I am recharging now and will for sure run another equalize. Can this be done back to back to verify maximum battery voltage has been reached?

A complete charge cycle will finish the bulk phase and run the entire absorb phase time (4 hours typical) before it would switch to float/complete. Then you can run an equalize charge.

With a couple of data points now you can track to see how the battery performs at any point in the future. What I do is twice a year, winterize and unwinterize I do a full capacity test and put it in my maintenance log. That way I know what shape the battery is in before I start the camping season, then what trauma I've inflicted during the season when I store it. If you take notes as to specific times and terminal voltages during the course of the test you can do interim abbreviated tests (say down to 12.0V) and see how closely the elapsed time lines up to the last test. Probably overkill for the most part unless you're cycling the hell out of your batteries.

The 2nd capacity test will be dialed down to the recommended draw 13% of Ah) = 8-9A.

You lost me on this one.

Mark B.
Albuquerque, NM

Good morning, I used this to find the wattage req'd for the 20 hr run.

 

[Mark_K5LXP]

Still not getting it. The reference cited is for charging, not discharging.



Mark B.
Albuquerque, NM

 

[Gary RV_Wizard]

Wow, great news but a little disappointing that my base info is out to lunch. Google told me: CCA÷7.25=Ah and I've been running with 93 Ah ever since. I will research how to use RC to determine Ah.

Converting either CCA or RC to AH is merely an approximation. RC to AH is distorted a bit by the Puckert Effect and the fact that amperage vs voltage is a curve rather than a straight-line. And CCA is even further afield, having a higher degree of those same distortions plus it is measured at 0F rather than 77F.

But the biggest capacity factor is the age of your battery. The CCA rating was established when new and 93 AH is about right for a Group 27 size battery, which are typically in the 95-105 AH range when brand new. If you still have 67 AH at age 5, you are doing OK as far as battery health is concerned. But the fact remains you have lost a substantial amount of energy storage capability over the years.

 

[Pass me]

Yer right on not sure why I did that.
I now know my LAB is rated @ ~70 Ah. (Thanks for the help discovering this using RC!) The next capacity test will be 3.5A/42W draw for 20 hr....so a 40W bulb.
I am currently performing another/final equalize run and will include the results when I post how this battery fares from the capacitys test.

 

[Gary RV_Wizard]

A decent rule of thumb is that a 12v inverter draws about 10% more wattage than it puts out (efficiency loss of 10%). That means the input amps @ 12v will be about 11x the output amps @ 120v.

 

[Ray-IN]

A spec equalize charge is time and current limited, and are generally recommended every four to six weeks for batteries in service. The amount of excess energy put into the battery amounts to some dissolved water, no chance of overheating and "warped plates".

Mark B.
Albuquerque, NM

Some battery mfgrs. state not to equalize charge them, Renogy AGM 12V batteries is specific about this.

 

[Mark_K5LXP]

I can only think of one AGM that has an equalize profile. It's almost exclusively an FLA process.

Mark B.
Albuquerque, NM

 

[Mark_K5LXP]

The next capacity test will be 3.5A/42W draw for 20 hr....so a 40W bulb.

You can always measure the DC going into the inverter and observe the current being pulled from the battery including inverter loss. An assortment of bulb wattages can get you very close to a target current draw. I know for my GC2 test with my inverter I use a 100W and a 25W bulb together.

Mark B.
Albuquerque, NM

 

[Mark_K5LXP]

Converting either CCA or RC to AH is merely an approximation. RC to AH is distorted a bit by the Puckert Effect and the fact that amperage vs voltage is a curve rather than a straight-line.

But at least with RC it's an Ah rating and not an approximation, just not Ah at the 20 hour rate.

93 AH is about right for a Group 27 size battery,

The RC is 160 which is 67Ah, for this to jump to 93Ah at the 20 hour rate would be a pretty high peukert number. My guess is it's closer to 75 to 80Ah. One could always test it to the RC spec at 25A and see how many minutes it goes. When I was testing GC2's as traction batteries I used a 75A load, the rate the Trojans used for their model names (T105 - 105 minutes at 75A).

Mark B.
Albuquerque, NM

 

[Pass me]

A decent rule of thumb is that a 12v inverter draws about 10% more wattage than it puts out (efficiency loss of 10%). That means the input amps @ 12v will be about 11x the output amps @ 120v.

So my 40W bulb would e better served using a 50W bulb type thing. A 50W draw would be more accurate in the capacity test.

 

[Mark_K5LXP]

Just the opposite - if the target current is say 3.5A @ 11.6V, P=I*E so that's 40W. But the inverter is going to consume some power, so the bulb you'd need is actually going to be a tad smaller. There's probably no way to know just what the efficiency of a given inverter is at this particular current, so just swapping in various combinations of bulbs and measuring with an ammeter will get you the closest. Another way would be to pick a bulb, say 40W and run 3 tests, and whatever run time you get (with say a fresh battery) becomes the baseline for that battery. Running the test with the same setup in the future and comparing run time will net you a valid power delivery value for comparison.

Candelabra, appliance, night light and other specialty bulbs come in a wide range of wattages. A handful of those plus some larger 25, 40, 60 ,100W gives you enough combinations to hit pretty much any current point you'd need. I keep my "test standards" and inverter in a box together so tests I do are using the same setup every time.

Mark B.
Albuquerque, NM