Goal Zero Vs. Dual Battery Vs. Solo Group 31

[Ducky's Dad]

Thanks.

 

[john61ct]

they seem to like their bulk charge and float to be on the aggressive side. My belief being Odyssey expects them to be abused and treating them gently might actually be harder on them.

Lots of subjective words there.

With quality AGM, the high amps are "coddling", proper care, as long as volts are kept within spec and watching out for heat issues. Nothing "aggressive" nor abusive there,

as long as you don't keep pushing Absorb long after dropping to endAmps.

Charging below .2C, even .3C I'd call anemic, no worries going higher except for safety / heat issues.

The top end of the voltage range is also fine, just don't trust charge sources, verify with known good calibrated volt meters periodically.

Yes regularly overcharging + going over voltage together for long periods will harm the bank.

There is no need to have a different (target) Bulk V different from (CV) Absorb,

and setting Absorb at the lower end of the range is better for when getting less cycled or in storage, while in active use toward the high end is better.

Relying on endAmps for benchmarking Full 100%, then a BM for staying above 50% SoC,

is more reliable than watching voltages.

 

[DaveInDenver]

Lots of subjective words there.

Indeed. Perhaps I should have said "It's my notably small survey opinion that the tolerable range for proper conditioning parameters of EnerSys batteries appears to be smaller and following an uncritical conditioning regime may be negatively impacting their lifespans to an extent beyond their competitive alternatives. YMMV."

I'm following their guidelines closely (although I do still use my stock Toyota charging system only modified to sense at the battery) without exceeding upper limits and I've still seen that the resting OCV has depressed. So, sure, I do speculate that being additionally nonchalant could be a long term issue. With Optimas you can drop them into any vehicle and they'll last at least a few years normally, which does not seem true of Odysseys for whatever reason.

 

[john61ct]

Well IME usually an alternator is rarely a major source compared to solar and genny, and the only ones I've relied on for deep cycling were setups modified for that purpose.

I know dozens of Odyssey banks and hundreds indirectly that routinely last 6-9 years in regular use before getting down to 65-75% residual capacity.

A couple/few years is no bar at all, if that's all you expect sure, get batts at big box.

And again, voltage is not usually an accurate indicator of anything, least of all a bank's state of health.

 

[Ducky's Dad]

When I first got my second generation Odyssey charger, I monitored it pretty closely with a multimeter, for volts and amps as it went thru its cycles. Everything seemed to be running according to spec, and the battery still won't get to full charge or hold a charge for any significant length of time. If I leave the truck parked for three weeks without charging or reconditioning the 2150, it drops to about 11.0V, sometimes as low as 10.6. Mine is not a sample of one, because I have had three 2150s, three big Odyssey chargers, two smaller Ctek chargers, and an Optimate charger that the battery wonk told me would be perfect for the 2150. The battery wonk supplies thousands of batteries every year to LAPD and LAFD, and the used Optimas that I have gotten from him after a couple years in police or fire service have lasted longer than my first two new 2150s. Jury is still out on the life span of the current 2150.

 

[DaveInDenver]

And again, voltage is not usually an accurate indicator of anything, least of all a bank's state of health.

What do you suggest be used instead?

 

[Ducky's Dad]

What do you suggest be used instead?
Odyssey suggests a carbon pile tester, but good ones are not cheap. I have an old school inductive heater battery tester, which is OK for my purposes. The hand held computerized testers are somewhat unreliable. A computerized test bench would be great, but completely impractical for most of us.

 

[DaveInDenver]

What do you suggest be used instead?
Odyssey suggests a carbon pile tester, but good ones are not cheap. I have an old school inductive heater battery tester, which is OK for my purposes. The hand held computerized testers are somewhat unreliable. A computerized test bench would be great, but completely impractical for most of us.

Testing current as a function of voltage through a resistance. And there's been offline battery impedance testers for a while. But for using in-situ there's not much practical measurement alternative to using voltage as an analog for status and condition. It's what the IEEE and SAE standards are mostly based upon anyway. I was curious what he meant, perhaps he knew of a online impedance box for automotive use, which would indeed be handy. As it is voltage is a well understood and basically reliable indicator, at least if you believe there are laws in chemistry and physics that must hold true.

 

[plh]

Being there are a lot of battery aficionados in this thread, How is capacity (AKA the Group 31 100+ amp hour rating) measured? Is it from full charge ~12.8VDC down to 10.5 VDC? or something else? Where is the 50% point 12.24 VDC or 11.64 VDC?

A couple of charts for pondering:

AGM State of Charge
Percent - Volts - Cell Voltage
100% --- 12.84 -- 2.14
95% ---- 12.78 -- 2.13
90% ---- 12.72 -- 2.12
85% ---- 12.66 -- 2.11
80% ---- 12.60 -- 2.10
75% ---- 12.54 -- 2.09
70% ---- 12.48 -- 2.08
65% ---- 12.42 -- 2.07
60% ---- 12.36 -- 2.06
55% ---- 12.30 -- 2.05
50% ---- 12.24 -- 2.04
45% ---- 12.18 -- 2.03
40% ---- 12.12 -- 2.02
35% ---- 12.06 -- 2.01
30% ---- 12.00 -- 2.00
25% ---- 11.94 -- 1.99
20% ---- 11.88 -- 1.98
15% ---- 11.82 -- 1.97
10% ---- 11.76 -- 1.96
05% ---- 11.70 -- 1.95
00% ---- 11.64 -- 1.94
-05% --- 11.58 -- 1.93
-10% --- 11.52 -- 1.92
-15% --- 11.46 -- 1.91
-20% --- 11.40 -- 1.90
-25% --- 11.34 -- 1.89
-30% --- 11.28 -- 1.88
-35% --- 11.22 -- 1.87
-40% --- 11.16 -- 1.86
-45% --- 11.10 -- 1.85
-50% --- 11.04 -- 1.84
-55% --- 10.98 -- 1.83
-60% --- 10.92 -- 1.82
-65% --- 10.86 -- 1.81
-70% --- 10.80 -- 1.80
-75% --- 10.74 -- 1.79
-80% --- 10.68 -- 1.78
-85% --- 10.62 -- 1.77
-90% --- 10.56 -- 1.76
-95% --- 10.50 -- 1.75


discharge to 10.5V
Amps Minutes Hours
25.0 -- 180.00 -- 3
16.8 -- 300.00 -- 5
9.30 -- 600.00 -- 10
5.10 -- 1200.0 -- 20
1.12 -- 6000.0 -- 100
1.00 -- 6720.0 -- 112

 

[DaveInDenver]

Yes, 10.5 V is the full discharge at which point 100% of the capacity is considered used. Going from (in Odyssey world) 12.84 V to 10.5 V is one full cycle for A-hr consideration. This is not something you should plan on because discharging this deep is hard on batteries so the recommendation is usually to discharge to a 50% point, which as you can see on your chart is how you get the roughly 11.64 V that smart people like dwh & Verkstad recommend.

 

[Airmapper]

And again, voltage is not usually an accurate indicator of anything, least of all a bank's state of health.

Testing current as a function of voltage through a resistance. And there's been offline battery impedance testers for a while. But for using in-situ there's not much practical measurement alternative to using voltage as an analog for status and condition. It's what the IEEE and SAE standards are mostly based upon anyway. I was curious what he meant, perhaps he knew of a online impedance box for automotive use, which would indeed be handy. As it is voltage is a well understood and basically reliable indicator, at least if you believe there are laws in chemistry and physics that must hold true.

What I want to know is why it even matters when most devices with such a feature (fridge, battery protectors) use voltage as the measurement by which they disconnect when they feel you are nearing an unacceptable level.

If I read 11.1V but I have say 60% left in the battery, (stupid numbers I know, but to prove a point) if my devices cut off, I still have a problem of a battery that can't can't keep things running. (Which is pretty much my feeling about my 2150...)

Going to try to run an overnight fridge test this weekend, I've got a small, low demand (35 watt when running, I figure ~3 amps when running) fridge. If it can't hold it's own overnight I'm going to be disappointed in my big 100Ah battery I got planning ahead for this very task.

 

[DaveInDenver]

What I want to know is why it even matters when most devices with such a feature (fridge, battery protectors) use voltage as the measurement by which they disconnect when they feel you are nearing an unacceptable level.

Voltage is easy to measure and plenty accurate to judge SOC in our non-critical use.

It's not as accurate as other methods (such as impedance) to judge true state of health but absent test equipment or the ability to remove a battery from service it remains as a reasonable indicator when you follow the typical charge/rest/test procedure.

If you're dealing with banks of hundreds of batteries installed in thousands of locations, such as telecom UPSes, then you want a way to really know SOH and SOC because you're churning through thousands of batteries. Then +/- 0.1% prediction accuracy is valuable. When you're trying to decide a fridge shut-off point it just doesn't need a scientific level of understanding. Using voltage isn't that far off that 12.4 V is magically showing a healthy battery when you expect +/- 12.8 V coming off a charge cycle.

 

[john61ct]

There is only one way to measure State of Health without thousands of dollars worth of lab grade equipment.

20 Hour Capacity Test:

An accurate AH counter can be used, but not necessary, just an ammeter and a stop watch.

#1 Benchmarking to 100% Full is straightforward, hold Absorb until trailing current drops to endAmps. If not mfg spec'd I use .005C, .5A per 100AH.

Then equalize if appropriate, and allow the batt to rest disconnected for at least 24 hours

#2 Make certain battery temperature is between 75F & 80F

#3 Apply a .05C load = Ah Capacity ÷ 20 (small light bulbs and/or resistors can work)

#4 Connect an accurate digital volt meter to the positive and negative battery terminals

#5 Start DC load and a stop watch at the same time

#6 As battery voltage drops, during discharge, adjust the DC load to maintain as close to the C÷20 rate as is humanly possible

#7 Immediately stop the discharge test when battery terminal voltage hits 10.499V

#8 Note the hours and minutes of run time on the stop watch and figure your percentage of 20 hours that it ran. This is your batteries Ah capacity or state of health as a percentage of the "rated" capacity. For example if a 100Ah battery ran for 16 hours it's testing at 80% of its original rated capacity. By industry standards lead acid batteries are considered “end of life” when they can no longer deliver 80% or more of their rating. They can still work beyond this point but are considered less safe and can be less predictable.

#9 Once you hit 10.499V recharge the battery immediately at the 20 hour rate. Once the battery is full, follow this up with equalization if appropriate

A long slow recharge (20 hour rate) can have a slight reforming effect on batteries and can actually serve to recover some lost capacity. It is not uncommon for a battery to have more capacity after a 20 hour test than it had going into it.

(Credit to Maine Sail)

 

[john61ct]

Yes, 10.5 V is the full discharge
…
discharging this deep is hard on batteries

No problem as long as it's not done frequently, and under controlled conditions, immediately after hitting 0% start recharging.

 

[DaveInDenver]

No problem as long as it's not done frequently, and under controlled conditions, immediately after hitting 0% start recharging.

Indeed, true. Just note that while a battery is rated for life cycles based on the number of 100% DoD cycles it will do before reaching an end of life capacity that's 80% of its rated or original capacity, doing this will be harsh and requires timely and proper charging to do. Odyssey says their cycle life testing assumes constant voltage at 2.45 V/cell for 16 hours at 1C between 100% DoD of discharges and temperature controlled.

In normal use doing less than 100% DoD cycles will mean the battery lasts relatively longer. The relationship is typically not linear and becomes very favorable at shallow discharges. I believe this is the basis for the 50% recommendation, to avoid needing exceptionally rigorous charging procedures and to reduce plate damage resulting from very deep discharges.

This just a generic example but holds true for most batteries. In it you'll see that if you only ever do 50% DoD cycles you'll get about 15% more cycles in the batteries' life and doing only 10% DoD gets you about 40% more life. And this assumes ideal conditions, which we know are rarely true in the real world. It's about determining the right size for your use find the right crossing point for cost vs. capacity for your system.