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Old 07-08-2014, 02:17   #46
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Re: Voltage Drop in AGM Under Load?

Clean all battery terminals, measure voltage at battery terminals under load with a multimeter, if your still getting a large voltage drop test batteries individually until you find a bad one. How often do you equalize you battery bank? A bank of that size should not get a voltage drop like that under such small c rate.
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Old 07-08-2014, 05:09   #47
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Re: Voltage Drop in AGM Under Load?

I just read through this and also went to the Gotcha Factor thread that Stu linked to and read that. My boat has all the things mentioned here (largish AGM bank, Link 2000, Link 10, genset, microwave, refrig, solar and wind) so I was very interested. Lots of great information that goes a step beyond what the manuals tell you! Many, many thanks to those like Stu and Maine Sail who have really studied this and are willing to share their knowledge in a way that's understandable to the rest of us. What a great resource!
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Old 13-08-2014, 05:53   #48
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Re: Voltage Drop in AGM Under Load?

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Originally Posted by neelie View Post
But earlier, I stated that batteries never go below 70%.
It looks like that the batteries are more likely run to lower than 50% capacity.
How often do you equalize the batteries and at what voltage?

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Originally Posted by neelie View Post
I actually built a 100AH battery to teach myself lithium. And I LOVE it.
Lithium would not give me these issues.
So what about using all that expertise you have gained, in getting that 100Ah battery to power the microwave?
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Old 16-08-2014, 10:06   #49
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Re: Voltage Drop in AGM Under Load?

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It looks like that the batteries are more likely run to lower than 50% capacity.

How often do you equalize the batteries and at what voltage?







So what about using all that expertise you have gained, in getting that 100Ah battery to power the microwave?

Hi Chala

1) I never equalize.. My rudimentary understanding is that this is not necessary on AGMs... .?? Am I wrong?

2) Too much work to connect up the Lithium pack to the inverter just for microwave.. Plus, even more obviously, the 100AH pack will struggle at 180A draw.. So not really a viable idea.. It's either all or nothing.. Makes no sense to mix chemistries. But I'm sure you knew that anyway and was just winding me up... .

3) What makes you say that my batteries are being run lower than 50%? I already stated that as per my BMS they never get below 70%.

I have changed the Peukerts exponent on the BMS to 1.12, I have adjusted the charge efficiency downwards to 90% and still my BMS tells me that I never get below 70%..

I have charged the batteries via the genset to 95% and then used the solar for 4 hours of floating and then manually synced the BMS... No change.. Still the lowest SOC us 70% first thing in the morning.

I can accept there are errors in the BMS's calculation of SOC.... But consistently a 20+% error? Surely not.

I float at 13.4V using the solar panels which are controlled by the best quality MPPT controller available.. Midnite Solar.

As I keep reminding myself, these are allegedly high end, heavy duty AGM marine batteries, designed for rough and ready use on boats. These are not some super dooper Unobtainium SecretOxide chemistry designed for some space vehicle and to be moly coddled by a bevy of PhD Engineers in a sterile laboratory.

Anyhow, to other helpful posters, I have still not yet dismantled the aft cabin bed to get to the batteries, other more urgent projects need to be completed first.
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Old 16-08-2014, 11:01   #50
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Re: Voltage Drop in AGM Under Load?

I can't pretend to be as expert as Maine Sail and the others who really are, but, I pretty much ignored the SOC on my Link 20 and Link 10 monitors even though I did the correct Peukerts and every thing else. I did monitor the battery voltage multiple times a day and made my own decision as to that being a superior data point in how well the batteries were doing. With the caveat is that I knew they would go way down with any big load, and that they would go up in the bulk/absorption/float charge cycle. But after they rested the voltage would either go up if I had a heavy load for a relatively long time and they set for a while after that, or, they would go down after a incomplete charge cycle.

If the batteries, after charge and after rest, would be at 12.7+ I took that to be close to as fully charged as possible given the age/condition etc. of the batteries. If it would not be at that then either I didn't charge them the right way/time or there is a problem. And after a microwave size load the volts would go down initially but should pop back up after, not to 12.7+ but certainly not to 12.4 or lower.

I did look at the SOC occasionally but considered it to be a calculation with too many possibly incorrect assumptions (Peukert, actual charge times at whatever voltage, etc.). And Maine Sail is the most reliable and knowledgeable guy on here (not to slight anyone else) but all he says smells right to me. His comment on the absorption cycle times is right as far as what Lifeline and others say.

I may have been wasting a valuable data point not using SOC but for me the voltage was best, given that I had to take in to account any other charging (like solar) and any other small or big loads that might be going on. But I would check it at night and basically shut most everthing down except a couple of lights. My AGMs lasted ten years and I loved them.
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Old 16-08-2014, 12:33   #51
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Re: Voltage Drop in AGM Under Load?

ExMaggieDrum.. Thanks for your input.

As far as the BMS goes, on the assumption that it's been synced to an approximately full battery. It merely counts the number of AH consumed, does some arithmetic and comes up with an SOC. There is no doubt that this number is not precise.. It's a guide..

But, I don't think that an expectation of +/- 5%tolerance for SOC is unreasonable.

It is very true that I do not know for sure that I am at 100%. At best, I can only assume it because my solar controller has gone into float phase. I have a 2 hour absorption phase before it will go to float.

Now accepting that the battery's are not 100% despite being in float. How far off can they be? Worst case they are only really at 90%SOC and the BMS has synced and now believes the batteries to be 100%.

I first noticed my problem with the fridge tripping out due low voltage when battery was at an indicated SOC of 80%. From the above assumption, the batteries are now at a real SOC of 72%.

My point being that I should not be getting such a huge voltage drop from a pack with remaining C at 540AH (72% of 750AH). Current draw was 180A (0.3 C)

Like yours, my battery voltage pops right back to normal after the high current draw. That is not my issue here.

I've just downloaded the Lifeline documentation and it has interesting charts of voltage drops versus load at various SOCs. Even with a massive 1C load (the 1 hour rate), at 30%DOD the voltage would be 12.07V. I'm not even within a bulls roar of that.

Which got me thinking that maybe, I have a dud battery in that parallel circuit.

Ps... Recently, we motored for over 12 hours. By all accounts, the battery should have been close to 100% and the BMS would have synced to that state. All I am saying here is that the BMS should be indicating SOCs which are not too far off.
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Old 16-08-2014, 16:05   #52
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Re: Voltage Drop in AGM Under Load?

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Originally Posted by neelie View Post
.....As I keep reminding myself, these are allegedly high end, heavy duty AGM marine batteries, designed for rough and ready use on boats. These are not some super dooper Unobtainium SecretOxide chemistry designed for some space vehicle and to be moly coddled by a bevy of PhD Engineers in a sterile laboratory.
...
Unfortunately there have been a fair number of premature AGM battery failures that took place in a short period time. I had a set that lost probably 60-70% of capacity in one year. They had been been well taken care of from a charging point of view. The manufacturer, Northstar, was useless in support and warranty. The distributor ended up backing them and doing me right.
The batteries would come up to full voltage, but in-shop capacity testing showed they had very little capacity left. Went witch Victron AGMs afterward and they lasted a long time.

Have you looked at the writeups on AGM batteries at morganscloud.com blog? Some interesting info, especially on desulfating Lifelines.
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Old 16-08-2014, 23:34   #53
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Re: Voltage Drop in AGM Under Load?

I want to restate what Maine Sail said for LA. You need to be at 14.4V AND the amps going in need to be below (I am not sure on this number for AGM ) at least 2% of the rated capacity.

A solar controller that stays in absorption for a certain time is not really good. I set my Outback (when I was still using LA) to stay in float until the amps dropped below 2% of capacity.

I ran into problemswith my LA the first year with my Victron 600 BM and solar. Towards the fall I had low votalges from my LA with high inverter loads and the Victron was telling me I was still at 80%. I found out that it re-synced to 100% when the sun was going down and the amps started dropping, while the voltage was still farly high, but not high enough. So every day the real SOC was going down a little bit. I had to really carefully tweak these parameters on the Victron BM:

Vc: Charged voltage. The battery voltage must be above this voltage level to consider
the battery as fully charged. Make sure the charged-voltage-parameter is always slightly below the voltage at which the charger finishes charging the battery (usually 0.2 V or 0.3 V below the ‘float’ stage voltage of the charger).
I find the 0.2-03V below way too much with solar. I went to 14.3 or 14.35 if that was an option.
It: Tail current. When the charged current value is below this percentage of the battery capacity (Cb), the battery can be considered as fully charged. Make sure this is always greater than the minimum current at which the charger maintains the battery, or stops charging.
You need to set this to the number Maine Sail recommended. I believe he wrote 0.5%.
Tcd: Charged detection time. This is the time the charged-parameters (It and Vc) must be met, in order for the battery to be considered fully charged.
I would set this to at least 5 minutes.

If the Victron synchronizes too early than your battery may have never been fully charged by solar and they may need to be equalized.

As for LiFePo. I have them now (8x700Ah Balqon). A friend of mine has the same installation and is in Grenada now as well. I just checked on marine traffic and see he just returned from Carriacou and is in Grand Anse Bay. The boat name is Kazaio. I am sure Gonzalo will be happy to give you a show of his LiFePo install and share his experiences with it.
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Old 16-08-2014, 23:42   #54
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Re: Voltage Drop in AGM Under Load?

BTW

I was getting frustrated too with the LA cutting dropping down so far that the autopilot would go into low voltage alarm during crossing. Had to tell the crew that coffee maker and toaster was not to be run at the same time. I did not want to woken u every morning when I was trying to catch up my sleep from the night watch because the tripped the autopilot.

To get experience I installed a small LFP system on my mono an then on the new cat immediately replaced the LAs with 1400Ah Balqon LFPs. Just a dream. My wife actually likes me a lot better now that she can swicth on whatever she feels like without me getting annoyed because of all the low voltage alarms.

LAs just suck with high loads. I can now easily draw 250A and the voltage barely goes down, maybe just to 12.8V when I am down to 80% SOC.
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Old 17-08-2014, 08:32   #55
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Re: Voltage Drop in AGM Under Load?

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Originally Posted by neelie View Post
ExMaggieDrum.. Thanks for your input.

As far as the BMS goes, on the assumption that it's been synced to an approximately full battery. It merely counts the number of AH consumed, does some arithmetic and comes up with an SOC. There is no doubt that this number is not precise.. It's a guide..

But, I don't think that an expectation of +/- 5%tolerance for SOC is unreasonable.

It is very true that I do not know for sure that I am at 100%. At best, I can only assume it because my solar controller has gone into float phase. I have a 2 hour absorption phase before it will go to float.

Now accepting that the battery's are not 100% despite being in float. How far off can they be? Worst case they are only really at 90%SOC and the BMS has synced and now believes the batteries to be 100%.

I first noticed my problem with the fridge tripping out due low voltage when battery was at an indicated SOC of 80%. From the above assumption, the batteries are now at a real SOC of 72%.

My point being that I should not be getting such a huge voltage drop from a pack with remaining C at 540AH (72% of 750AH). Current draw was 180A (0.3 C)

Like yours, my battery voltage pops right back to normal after the high current draw. That is not my issue here.

I've just downloaded the Lifeline documentation and it has interesting charts of voltage drops versus load at various SOCs. Even with a massive 1C load (the 1 hour rate), at 30%DOD the voltage would be 12.07V. I'm not even within a bulls roar of that.

Which got me thinking that maybe, I have a dud battery in that parallel circuit.

Ps... Recently, we motored for over 12 hours. By all accounts, the battery should have been close to 100% and the BMS would have synced to that state. All I am saying here is that the BMS should be indicating SOCs which are not too far off.
Neelie - the reason you need to put more absorption voltage into the batts is because you have to change the chemistry deep inside them. The higher voltage can push that reaction while the float does not provide enough to get it past an equillibrium point.

So - you are experiencing a SOC that is wildly different from the voltage. I think that makes my case as far as how useful SOC is in certain situations (like yours). I could be wrong but my two cents. It does sound like you may have a bad battery in your bank. You should check that ASAP as one bad one can screw us other good ones if left as a bad influence (like my brother).

Good luck. I have to go to the marina to get on a boat from here in WA to San Francisco. I am crewing with some friends and am supposed to be their "experienced" crew. We'll see.
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Old 17-08-2014, 12:19   #56
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Re: Voltage Drop in AGM Under Load?

Paul-
One has to ask, did you have an "AGM" failure? Or, do I recall Northstar as being the then-anonymous Chinese battery company that was making oddball AGMs topped off with gel?

I see their web site now is full of global distribution, TPPL emphasis, ISO certification...but don't recall seeing any of that some years ago. Or am I confusing them with someone else?
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Old 17-08-2014, 13:15   #57
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Re: Voltage Drop in AGM Under Load?

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Paul-
One has to ask, did you have an "AGM" failure? Or, do I recall Northstar as being the then-anonymous Chinese battery company that was making oddball AGMs topped off with gel?

I see their web site now is full of global distribution, TPPL emphasis, ISO certification...but don't recall seeing any of that some years ago. Or am I confusing them with someone else?
I haven't heard anything about gel/agm mixes. The batts I had were spec'd as AGM and they were not cheap knock-offs. They were spec'd slightly higher in capacity than others by weight, ie density. Either way, they suxed.
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Old 17-08-2014, 13:51   #58
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Re: Voltage Drop in AGM Under Load?

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Paul-
One has to ask, did you have an "AGM" failure? Or, do I recall Northstar as being the then-anonymous Chinese battery company that was making oddball AGMs topped off with gel?

I see their web site now is full of global distribution, TPPL emphasis, ISO certification...but don't recall seeing any of that some years ago. Or am I confusing them with someone else?

Northstar is a bunch of guys who left Enersys (Odyssey) and basically copied the TPPL technology. They are a US company and build TPPL AGM batteries...
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Old 17-08-2014, 20:12   #59
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Re: Voltage Drop in AGM Under Load?

I didn't find anything on a fast web search, except for some pages on the wayback machine that indicate Northstar was founded in Missouri in 2001 and manufactures all their batteries there. But somehow, is now a multinational global corporation, possibly merged or bought by SiteTel of Sweden.

I *know* that someone was selling agm batteries "topped" with gel instead of empty space, maybe five years back, but the search engines on sailing forums seem to be, well, less than Boolean angels.

"This" Northstar seems to be an all-USA ISO-certified prime manufacturer, and normally that would mean there's also an ISO mechanism in place where they actively seek feedback on failures and fixes. Surprising they didn't at least try to investigate the failure with you, although if they didn't intend your batteries as "marine deep cycle"...maybe they just don't want to know.
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Old 18-08-2014, 10:37   #60
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Re: Voltage Drop in AGM Under Load?

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I didn't find anything on a fast web search, except for some pages on the wayback machine that indicate Northstar was founded in Missouri in 2001 and manufactures all their batteries there. But somehow, is now a multinational global corporation, possibly merged or bought by SiteTel of Sweden.

I *know* that someone was selling agm batteries "topped" with gel instead of empty space, maybe five years back, but the search engines on sailing forums seem to be, well, less than Boolean angels.

"This" Northstar seems to be an all-USA ISO-certified prime manufacturer, and normally that would mean there's also an ISO mechanism in place where they actively seek feedback on failures and fixes. Surprising they didn't at least try to investigate the failure with you, although if they didn't intend your batteries as "marine deep cycle"...maybe they just don't want to know.
They were aware of the failure. They had the distributor/seller do a lot of bench testing/desulafting/charging and sending results back. But the manufacturer was useless on the warranty.
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