AGMs and Dumb Regulator . . .

[stevensuf]

ColeMJ , the boat is an ex charter so yes the batteries were charged almost exclusively by the alternator.

Here in the UK things are a little bit more expensive! Try $250 for a smart reg!

Maybe ill build an auto system with a current sensor and switching relay, can't be too difficult , a normally closed relay (ie should it fail it will still connect) add a current sensor so that when the current falls off it activates the relay sending the power via the diode thus reducing the input voltage and current.

I should be able to build one for under 20 UK pounds (US$30), versus $250 for a sterling or the like .

A 100amp diode about 5 uk pounds, 100a relay 4uk pounds, current sensor 80p, potentiometer (variable resistor) 80p , small transistor to switch relay, 50p, bit of breadboard and small heat sink for the diode- 5 pounds.

We are certainly paying well over the odds for marine electronics!

(ps i do have a hons degree in electrical engineering)

[stevensuf]

Go boating now- the advantage is see with agms is 10-15% less loss in charging and also i can fit 440AH of agm in my battery space versus 360AH of LA.

I have 320w of solar to install and a mppt controller with temp sensor, should gain another 10% over a normal regulator. The little tweaks all add up, agm and mppt should see a good twenty percent extra AH per day vs LA and simple regulator.

I have the option of a used duogen (wind/tow gen) which should help at night and on longer passages, Hence i am not too bothered about fitting fancy alternator systems,

I just don't want the 14.4v from the alternator to fry the agms on the odd occasions where i have to motor for extended periods!

[colemj]

Originally Posted by stevensuf

ColeMJ , the boat is an ex charter so yes the batteries were charged almost exclusively by the alternator.

Then they were killed by undercharging - motoring around at 14.4V during the day, even every day, wouldn't have killed them.

Here in the UK things are a little bit more expensive! Try $250 for a smart reg!

I just looked at Sterling in the US and EU store. They are more expensive (127euros+shipping vs. 93USD+free shipping). Funny for a company and product based in the UK.

Maybe ill build an auto system with a current sensor and switching relay, can't be too difficult , a normally closed relay (ie should it fail it will still connect) add a current sensor so that when the current falls off it activates the relay sending the power via the diode thus reducing the input voltage and current.

I should be able to build one for under 20 UK pounds (US$30), versus $250 for a sterling or the like .

A 100amp diode about 5 uk pounds, 100a relay 4uk pounds, current sensor 80p, potentiometer (variable resistor) 80p , small transistor to switch relay, 50p, bit of breadboard and small heat sink for the diode- 5 pounds.

We are certainly paying well over the odds for marine electronics!

(ps i do have a hons degree in electrical engineering)

Great! You will be able to pull off a nice project. Post the details when you are done please, so we can all learn.

Mark

asdfjkl

[Maine Sail]

Originally Posted by stevensuf

The ones that came with the boat are lifeline agms 200ah (x2). They manage to run the fridge and a few other things for about 4 /5 hours before dropping under 12v, from being left on charge for a few days... they are pretty dead!

I think I will add an extra diode on the alternator output with a bypass, this should drop the voltage to 13.8v and back to 14.4 when i switch the bypass on.

Now what would be worse for battery life? constant overcharging or occasional under charging?

How long are you running the engine? Do you have a sailboat or trawler? The most common cause of AGM death I see is chronic under charging leading to sulfation not over charging via a 14.4V alternator on a sail boat.

If your batts are Lifeline they advise against "trickle charging" but if you leave loads on at the dock it may be necessary.

A purpose built charger or regulator that can be programmed for your bank, with temperature compensation, is a very wise idea not only for your AGM's but also for your alternator.

Still you'd need to run the engine for a loooong time, and do this often, to destroy Lifeline's at 14.4V, unless of course they are in a hot space, like your engine bay, and are not temp compensated...

You probably need to do a conditioning/equalizing charge if they are Lifeline's before pronouncing them dead...

That being said you are not the first and probably won't be the last to see short life with AGM's.

[Cruisin Cat]

Originally Posted by goboatingnow

Why use AGMs. Other then spillage they offer nothing for boats in reality.

The reason I use AGM's is that the top of the batteries is very difficult to access in my battery compartment. Also, AGM charge acceptance rate is much higher so I get a higher SOC after x hrs of sunlight on solar cells

[colemj]

Originally Posted by Cruisin Cat

The reason I use AGM's is that the top of the batteries is very difficult to access in my battery compartment. Also, AGM charge acceptance rate is much higher so I get a higher SOC after x hrs of sunlight on solar cells

The first is a very valid reason for AGMs. The second is incorrect unless you have a very small battery bank or an extremely large solar array.

The higher charge acceptance is a red herring for AGM preference for most cruising boats because most boats can't generate enough charge to take advantage of the higher acceptance rates for the average cruising battery bank of 400-1000 Ah capacity.

Mark

[Cruisin Cat]

Originally Posted by colemj

The first is a very valid reason for AGMs. The second is incorrect unless you have a very small battery bank or an extremely large solar array.

The higher charge acceptance is a red herring for AGM preference for most cruising boats because most boats can't generate enough charge to take advantage of the higher acceptance rates for the average cruising battery bank of 400-1000 Ah capacity.

Mark

Well Mark, I'm glad we see eye to eye on the first point

However, I don't entirely agree with you on the second point. What you said is true for when the battery bank SOC is below 85% - 90%....not many cruising sail boats have charging systems that can exceed the acceptance rate of any type of battery bank if it's SOC is < 85% to 90%.

But, as somebody said above, the main cause of battery failure on sail boats is undercharging, so if you want to minimise this you need high acceptance rates above 85% to get SOC up as high as possible each day. For example, I previously had sealed lead/calcium batteries on my boat and when SOC got to around 90% their acceptance was <1% of bank capacity. With AGM's at 90% SOC, acceptance rate is still >5% (which is the max output from my solar cells). In case you're wondering....I did have the voltage regs set to higher voltages when I was charging the lead/calcium batteriess.

Barrie

[Maine Sail]

Originally Posted by Cruisin Cat

Well Mark, I'm glad we see eye to eye on the first point

However, I don't entirely agree with you on the second point. What you said is true for when the battery bank SOC is below 85% - 90%....not many cruising sail boats have charging systems that can exceed the acceptance rate of any type of battery bank if it's SOC is < 85% to 90%.

But, as somebody said above, the main cause of battery failure on sail boats is undercharging, so if you want to minimise this you need high acceptance rates above 85% to get SOC up as high as possible each day. For example, I previously had sealed lead/calcium batteries on my boat and when SOC got to around 90% their acceptance was <1% of bank capacity. With AGM's at 90% SOC, acceptance rate is still >5% (which is the max output from my solar cells). In case you're wondering....I did have the voltage regs set to higher voltages when I was charging the lead/calcium batteriess.

Barrie

Perhaps your method of determining SOC was incorrect, your bank was heavily damaged or your controller or regulator reducing the voltage far to early resulting in low current? Less than 1% acceptance is basically full.

The wet cell bank on our boat takes about 6-7%+ at 90% SOC and declines until it is accepting less than .5% at 99-100% SOC (voltage dependent). I have seen little difference in acceptance rates between wets and AGM's above 90% SOC. I get to see this sort of thing daily on many different boats and many different charging systems.


I am heading out sailing right now and will try and drop 10% out of my bank to 90% SOC, then make a video for you... What you saw, less than 1% acceptance at 90% SOC, is not normal..

[Cruisin Cat]

Originally Posted by Maine Sail

Perhaps your method of determining SOC was incorrect, your bank was heavily damaged or your controller or regulator reducing the voltage far to early resulting in low current? Less than 1% acceptance is basically full.

The wet cell bank on our boat takes about 6-7%+ at 90% SOC and declines until it is accepting less than .5% at 99-100% SOC (voltage dependent). I have seen little difference in acceptance rates between wets and AGM's above 90% SOC. I get to see this sort of thing daily on many different boats and many different charging systems.


I am heading out sailing right now and will try and drop 10% out of my bank to 90% SOC, then make a video for you... What you saw, less than 1% acceptance at 90% SOC, is not normal..

Maybe you're right....some defect in my old lead/calcium batteries could have caused or at least contributed to low acceptance rate problem. Interested to see your video.

[Maine Sail]

Originally Posted by Cruisin Cat

Maybe you're right....some defect in my old lead/calcium batteries could have caused or at least contributed to low acceptance rate problem. Interested to see your video.

Only got the bank down to 94% but she was still taking about 20 amps +/- which is about 7% acceptance between 94% and 95% SOC. No loads were on, sloar and combiner turned off. Bank was 100% full when I got there having been charged via solar with a Genasun MPPT...

Will try to upload the video, but it is quite boring..

[hellosailor]

I'm suspecting that the "low acceptance rate" when 90% charged batteries were being charged fro a conventional "automobile integral" alternator, is in fact nothing to do with the acceptance rate of the batteries, but rather this sounds like the conventional alternator saying "they're nearly at 13.8 now, I'll really cut back on output power".

Not what the batteries can absorb--but the miserly bit that the alternator puts out to prevent them from being overcharged in that situation. 100% SOP.

[goboatingnow]

+1 hellosailor. Like I said AGMs really offer nothing to boat systems. They were designed initially for military aircraft, where issues like inverted use , resistance to leakage when bullet ridden and low self discharge are very useful. But very limited applicability in boats. ....!

Dave

[Maine Sail]

Originally Posted by hellosailor

I'm suspecting that the "low acceptance rate" when 90% charged batteries were being charged fro a conventional "automobile integral" alternator, is in fact nothing to do with the acceptance rate of the batteries, but rather this sounds like the conventional alternator saying "they're nearly at 13.8 now, I'll really cut back on output power".

Not what the batteries can absorb--but the miserly bit that the alternator puts out to prevent them from being overcharged in that situation. 100% SOP.

Can you or someone please explain in detail, electrically, how this happens? I have tested lots of auto alts and find the regulators simply regulate or limit the voltage to a preset voltage limit. They have two stages bulk and absorption or wide open/CC and voltage limited. If you have an antique alt with a low set point like 13.6-13.8V you will chronically undercharge the batts and there is no way around that. A dumb regulator with a 14.2+ set point will work well, though it will lack other features that only an external reg can offer like temp compensation.

Most alts for the last 20+ years have been coming through at 14.2V+. I have even compared a dumb regulator to a "smart" at the same voltage set point and the field voltage and current were nearly identical. The batteries decide what to accept once the alt reaches the regulators set point.

I have also done exhaustive A/B comparisons between smart and dumb regulators, on the same alternator, with two batteries discharged in parallel to the same DOD. I set them to the same absorption voltages and, like Practical Sailor found, I saw no faster charging and no "cutting back" by the dumb regulators if all is "equal" in terms of the voltage set point. In bulk both regs performed virtually identically. Below the voltage set point both regs apply enough field to run them to full output and I found this was only limited by the alts physical temp. Both scenarios yielded charge curves that were barely discernible as being different..

They simply limit voltage, that is all they know. Some regulators have built in thermal protection, which can limit the field, but I've not seen it very often in marine alts.

A couple of years ago I spent nearly an entire Saturday throwing random dumb regulated alts into a large test machine with a huge heat sink and loading them up. Every single dumb regulator had the ability to throw enough field at the alt so the alt put out its rating, and often times, even beyond what the alts rating was when cold. Even when heated up to over 200f the dumb regulators continued to push the alts to work to their full potential provided I applied enough load to keep it from hitting its voltage limit.. When loaded up many alts hit 200F pretty quickly..

I install lots of alternators and smart regulators, did one just last week, but on my own boat, with basic wet cells, I still have, gasp, a dumb regulator. I know I am sooo crazy.. The reality is that I have no need for anything more. Sure my bank will take more in bulk than what I can currently give it but I really don't need it as our energy use is quite minimal and we supplement with solar.

Our dumb regulated alt does not cut back it simply gives the batts what they will take or will accept. This little 50A Mitsubishi alternator has over 30k nm on it and has traveled from Newfoundland & Labrador to South America, through the canal and up to Alaska. It's also been across the Atlantic and still keeps ticking.. The only thing that holds my alt back is when it warms up and puts out 40-43A as opposed to its rating of 50A. If I deplete to 50% SOC it will pump 40+/- until the voltage comes up then the batteries start declining acceptance but even then it is still pumping out WAY more than 1% acceptance.. At 94-95% SOC it is still pumping in 20A +/- into our 375Ah bank.. Not bad for an alt that "cuts back"..

Can you please explain electrically how what you've stated actually happens because I have tested this every way from Sunday and just not seen it happen that way.

This winter I will likely install an Electromaax alt & serp kit, not because I need it, I don't, but more so to show customers who do need it what it is and how it works.

For 3200 engine hours our little dumb regulated alt has performed very, very well.. The only change has been to direct wire it to the house bank with 4GA wire...

[btrayfors]

The amount of amperage a battery will accept depends on the type of battery, it's state-of-charge (SOC), its condition (health) and, most directly, the applied voltage.

The amount of amperage a given battery bank will accept at, say, 95% SOC is directly related to the voltage output of the charging source. The higher the voltage, the more amperage the battery bank will take...up to a point.

Here are some real world numbers from a quick & dirty test in my shop this evening.

Pair of T-105's and a 50A battery charger with variable voltage output:

@ 13.6VDC......................10.6A

@ 13.9VDC......................11.4A

@ 14.17VDC.....................17.2A

@ 14.67VDC.....................17.7A

Thus the acceptance rate of this small T-105 bank (225AH) ranged from 4.7% of capacity @ 13.6VDC to 7.9% of capacity @ 14.67VDC.

Voltage measurements were taken with a Fluke 189; amperage measurements with a Fluke 337.

Bill

[stevensuf]

Oe advantage of agms many people apear to miss is the fact that they have a lower internal resistance compaired to normal lead acids, so you can save about 10-15% in charging time.