Is it as simple as Ah in Ah out for figuring SOC?

Dan_ · January 2015

I have a Victron battery meter. It assumes battery is full when float voltage is held for a minute or two and then resets Ah counter to 0.

My questioning though is battery charge state as simple as Ah in Ah out? For instance, say battery is at 100%, 25Ah is taken out, then 25Ah is put back. Back to 100%?

My guess is that its not that simple. Seems like the voltage at which those amps are applied would vary how well the battery bank accepts the charge.
Your thoughts?

BB. · January 2015

Re: Is it as simple as Ah in Ah out for figuring SOC?

It sort of is... A lead acid battery is near 100% efficient when using Amp*Hours as your measurement tool.

It is Watt*Hours in/out that are not. For example (pick your discharging/charging average voltages):

100 AH * 12 volts discharging = 1,200 Watt*Hours
100 AH * 14.5 volts charging = 1,450 Watt*Hours

1,200 WH/1,450 WH = 0.83 Energy Efficiency

However, when gassing the batteries (near end of charge/during equalization), AH efficiency will drop tremendously (gassing does not charge the battery--Energy wise).

-Bill

706jim · January 2015

Re: Is it as simple as Ah in Ah out for figuring SOC?

My old Trace C40 charges at high voltage cutoff for two hours before dropping down to float voltage.

One minute seems kinda short.

SandyP · January 2015

Re: Is it as simple as Ah in Ah out for figuring SOC?

Dan_ wrote: »

I have a Victron battery meter. It assumes battery is full when float voltage is held for a minute or two and then resets Ah counter to 0.

My questioning though is battery charge state as simple as Ah in Ah out?

If you have the BMV-600 meter then there is a setup value for the battery charging efficiency - currently I have mine set on 95% however this appears to be 1-2% too low as it will reset at 99% charged based on the amps into the battery dropping to 1% of the batteru Ah cappacity (also a setup value in the Victron BMV-600.
I have recently started logging the data from the BMV and will post a picture of the graphed output showing the jump to 100 SOC.

regards, SandyP

gww1 · January 2015

Re: Is it as simple as Ah in Ah out for figuring SOC?

Bill

However, when gassing the batteries (near end of charge/during equalization), AH efficiency will drop tremendously (gassing does not charge the battery--Energy wise).

It seems that voltage plays an important part in this also. I EQ last night and brought my batteries sg to full. The battery was 64 degrees and the sg on the low cell was 1.292 and the high was over 1.300. The next morning after running loads the trimetric said 80% soc and about 177 ah was taken from the battery. The battery temp was 50 degrees and the sg was a little over 1.240. By noon with a charge rate of about 65 to 70 amps for a couple hours the voltage was 60 volts and the sg was almost to 1.250 The next three hours the batteries stayed above 61 volts but not my absorb setting of 61.6 volts. I only got one full hour of absorb. after the batteries were above 60 volts I seemed to gain about .010 of sg per hour.

I have the trimetric set at a 90% eficiancy rate and just barily replaced the amps that were drawn out at that rate. The end result was a ten degree raise in bat temp to 60 degrees with an end sg of 1.272. With out the higher voltage used for eq I don't think the sg would go up for a long long time. As it was the bat was only excepting 6 amps and when eq it gets to only accepting 10 amps. When I eq last night the bat. just barily equalled out the previous used amps but got the sg up. today it equaled the amps out but at a lower voltage and the sg was only 1.272.

They bats were at the end of three days with out a more then 90% charge each day and today was from a shallow discharge.

Keep in mind that I am not charging with temp compensation. They say you can bring a sulfated battery back with a very low amp and very long charge. My belief is that sg doesn't seem to rise without the correct voltage. I am sure there are varibles to this as I have gotten to some pretty high voltages with some very long extended low rate charging. I didn't have the trimetric when that happened so have no way to compare what was taken to what was put back to get those high voltages.

Some day I might figure this out.
gww

BB. · January 2015

Re: Is it as simple as Ah in Ah out for figuring SOC?

I would not lay odds on being able to bring back a sulfated/taken to zero state of charge battery to anything resembling useful capacity.

If it was a new battery taken "dead", maybe (usually with less than full capacity and expected life). Battery with more than a year or two on it, much less likely to recover.

Do we hear experiences (and the use of special chemicals, slow/fast/hard/soft charging/cycling)--Yea. If somebody has the time and energy, certainly OK to try.

Even have read about people that convert Lead Acid to "alkaline" electrolyte. From a 7 year old post of mine:

I read one guy/place that used some sort of caustic to convert a dead lead acid battery to an "Alkaline" Lead Acid battery (rinsed out acid electrolyte and replaced with alkaline electrolyte"... You can read about the process here--I stumbled on the website last week. I have no idea if this is safe or works at all, or if the poster is full of hot air--use at your own risk.

Will it work... Don't know. Would I bother--Maybe when the world has ended as we know it (and I am still around and "care").

-Bill

gww1 · January 2015

Re: Is it as simple as Ah in Ah out for figuring SOC?

Bill
was your post ment to be on this thread?
Cheers
gww

BB. · January 2015

Re: Is it as simple as Ah in Ah out for figuring SOC?

gww1 wrote: »

Bill
Keep in mind that I am not charging with temp compensation. They say you can bring a sulfated battery back with a very low amp and very long charge. My belief is that sg doesn't seem to rise without the correct voltage.
gww

That is what I was answering.

-Bill

gww1 · January 2015

Re: Is it as simple as Ah in Ah out for figuring SOC?

Bill
Ok, I had just read that some where, thanks for your thoughts. It was the 100% discharge in your post that threw me. I wish I had left that part out as I was most curious about the voltage relationship to getting sg up regardless of amps replaced and wondered if my experience was normal. I almost posted a differrent thread on that question but it seemed to fit here.

Not what I an interested in but just a side note. The gb battery web site says;

Never allow a battery to go completely dead (unusable). It will take over 72 hours of continuous charging to bring back to full charge, and may require shop service to restore full charge.

Thanks
gww

SandyP · January 2015

Re: Is it as simple as Ah in Ah out for figuring SOC?

OK, here is the plot of the Victron BMV-602S data:

Attachment not found.

SandyP · January 2015

Re: Is it as simple as Ah in Ah out for figuring SOC?

BB. wrote: »

It sort of is... A lead acid battery is near 100% efficient when using Amp*Hours as your measurement tool.

It is Watt*Hours in/out that are not. For example (pick your discharging/charging average voltages):

100 AH * 12 volts discharging = 1,200 Watt*Hours
100 AH * 14.5 volts charging = 1,450 Watt*Hours

1,200 WH/1,450 WH = 0.83 Energy Efficiency

However, when gassing the batteries (near end of charge/during equalization), AH efficiency will drop tremendously (gassing does not charge the battery--Energy wise).

-Bill

Hi Bill,

Using the data logged every second by the Victron BMS it shows that from 100% SOC on the afternoon of the 3rd Jan'15 through the discharge and recharge cycle back to 100% SOC on the afternoon of the 4th Jan'15 some 3,303 WH was drawn from the battery and then 3,517WH was put back into the batteries - does this make these batteries around 93.9% efficient?
Regards, SandyP.

BB. · January 2015

Re: Is it as simple as Ah in Ah out for figuring SOC?

Yes... ~90% is not bad for a good battery and one that does not spend too much time >90% state of charge while "charging".

Assuming that the batteries are being fully charged (>90% state of charge 1-2 per week or so).

I use 80% for flooded cells during design--Allows for batteries that cycle at higher states of charge, and as batteries age, they get less efficient (just being conservative).

Use 90% for AGM, which have been seen to go as high as 98% efficiency during charging (AGM have lower voltage drop when charging, and are not "gassed" like flooded cell batteries).

-Bill

Is it as simple as Ah in Ah out for figuring SOC?

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