AGMs and Dumb Regulator . . .

[stevensuf]

My batteries are dud,they are agms, i've checked the alternator output and it is 14,4v fixed, simple reg.

I am assuming this has hastened the battery life.
Now id like to replace the agms with agms, but i dont fancy the shortened battery life that 14,4v non stop would cause.

I'm thinking a simple cheap solution, would be to add an extra diode in the charging circuit (make it switched) so i can manually drop the voltage by 0.65v by adding the diode to the loop, sounds much cheaper than a smart controller..

Any thoughts? good or bad idea?

[Paul L]

Why not add a smart regulator and a smart charger? It will significantly extend the life of the AGMs. And given the cost of the batteries, seems like a wise investment.

[stevensuf]

The point is to avoid expense! The Extra cost of the smart charger is almost as much as the batteries!

I'm hoping the 320w of solar I am installing will cope with most of my charging requirements, so really dont want to spend double the cost of the agms on a smart charge/regulator that will rarely be in use.

Im thinking of a way to stop the alternator over charging the agms on the odd occasion i need to motor for a long duration.

Granted doing it manually ill have to remember to switch it over.
Maybe i should just go with cheaper flooded cells.. no fancy regulator required just top up regularly!

[Seahunter]

Smart charge with standard wet cells. You'll get more AmpHrs and reliability, cheaper albeit with a little more work. However, what makes you think the AGMs are "dead"? Most times they're not.

[DeepFrz]

steven, keep us in the loop and let us know how it works for you.

[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?

[Cruisin Cat]

Good question!

I have agm's on my boat and two dumb internal regulators that come standard with volvo engines. Most of the time my batteries are charged by solar and wind so very seldom run the engines for charging.

On the rare occasions when I have to motor for a long period it just requires a bit of discipline to watch the charging current. My agm's are Lifeline and their charging spec is...
- bulk charge at 14.3V (+/-1V) until charging current is <0.5% of capacity, then
- float charge at 13.3V (+/-1V).

So putting a diode in the charging circuit won't overcome the problem that when charge current falls below 0.5% of bank capacity you need to either stop charging the batteries or at least reduce charge voltage to around 13.5V, ie float charge.

On a long passage into the wind like Panama to Galapagos (900nm motor sailing) I watch the charge current and when it gets down to around 0.5% I shut off the engine (only run 1 engine while motor sailing) bear off the wind and sail for just 30min. In this 30 min period I turn on everything that consumes power and the bank SOC will drop from 100% to 96% - 97%. Then restart the engine and motor sail for 3 or 4 hours before I have to repeat the process. Dropping only 3% or 4% doesn't sound like much but it is surprising how long it take to put the last few % back into the batteries....the charge current at this time is around 0.8% (and very slowly reducing towards the magic 0.5%).

This seems to work for me and it isn't really a hassle...after a couple of cycles you know pretty well how many hours to run the engines before current will get below 0.5%.

Forgot to mention....you need to shut off all other charging systems (eg solar, wind) during the 30 min battery draw down, otherwise they will just supply all the power and battery SOC wont drop much. I shut them off and leave them off for the whole of any motor sail passages.

[stevensuf]

Thanks for the advice cruising cat, good to remember to switch off the solar, nb the diode dropping the voltage to 13.8 will drop the charging current compared to 14.4 by a considerable amount, the agms im looking at recommend a float of 13.4-13.7 so i doubt 13.8 wont do too much damage!

Bear in mind the charging current is directly related to the charging voltage, constant current chargers work by slowly upping the voltage of the output as the battery charges to maintain the same current flow.

[Seahunter]

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!

Is the proper charge getting to them. Did you clean all the terminals and check the battery cable continuity and connections?

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

Go to Lifeline's website and download the manual for your specific batteries. The charging volatage needs to be as indicated along with float voltages. Most AGMs cannot be equalized so make sure your charger is set NOT to equalize.

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

This seems to be an ongoing argument. However, if constant charging was okay, why do chargers have a "float" setting? My opinion, charge your batteries according to manufacturers specs; most tell you not to overcharge.

[stevensuf]

Seahunter:
They are definitely done for, holding very little charge, connections are all good, checked them all, charger ok, alternator ok, id say im getting about 50 amp hours out of them before they slip under 12v

[hellosailor]

steven, no matter how dumb the alternator's internal regulator may be, it should have a voltage sense lead that runs from the alternator to the battery positive. With many boats this is just connected to the alternator output, effectively disconnecting it, because the sense lead must be switched to each battery bank if you have two banks, and that costs a little more.

If you connect the sense lead (i.e. by using a battery switch that has an extra "field sense" contact set, and using that for the sense lead) so the alternator can actually see battery voltage, it will do a much better job.

The automobile type internal regulator is actually designed to "not overcharge" an SLI battery suring long road trips, and that usually works as long as the sense lead is hooked up and used. But this also means it normally never puts a full or fast charge on the batteries, and that also shortens their life.

So using a proper regulator for deep cycle batteries is not just a matter of not overcharing them, it also ensures they will be fully charged--unlike the automobile regulator, which may take hours and hours to put the last 10% back into a battery.

Lifeline is also one of the very few companies that instruct customers to perform a regular equalizing charge (i.e. about 15 volts) on their AGM batteries. There's no way to easily do that with an internal regulator, and it could be that is part of why your AGMs are not holding a good charge.

With the cost of batteries going up so high, and likely to be higher again the future, investing in a good external regulator that charges correctly may not be a bad idea. Manually flipping back and forth and guessing battery charge state simply will not be as good for the batteries. If there's any way to ante up and buy a proper regulator...it may be the best investment, long term.

[Cruisin Cat]

Originally Posted by hellosailor

Lifeline is also one of the very few companies that instruct customers to perform a regular equalizing charge (i.e. about 15 volts) on their AGM batteries.

The lifeline tech manual that I read does not recommend regular equalisation...it recommends equalisation only when there is evidence of loss of battery capacity

[colemj]

The 14.4V constant alternator output was not the cause of your dead AGM's unless you have been running your engine 24hrs/day for a week or more.

If you feel the need to cut the alternator output, simply put a disconnect switch on the field wire. That way you don't need to kill the engine to stop charging.

A Sterling smart alternator controller can be added to an internally regulated alternator for $95USD - probably equal to, or less than, what you would pay for a suitable diode bank, heat sink and switch to do what you want to do (you weren't thinking of just putting a simple electronics diode directly into the charging circuit, were you?).

Mark

[FlyingCloud1937]

The dumbest regulator is.

The one whom thinks he can do a better job than a purpose built regulator, that will on average outlast 4 well maintained bat banks, for a 1/3 the cost of first bank. Which will also provide temp compensation, as well as voltage regulation, as well as stop the alternator from over temping.

The old saying is more true in this regard than ever. "pay now...or pay 5 times over all" plus labor, plus inflation.

There is not a sole whom can out perform a purpose built regulator, if ya buy a quality piece of merchandise....think balmar!!!

Lloyd

this is just a ridiculous conversation

if this was just the bat in your auto, then fine...but it's not.

[goboatingnow]

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

The other thing is AGMs are very sensitive to undercharging and to overvoltage. It's suprising how easy it is to kill AGMs. ( see several AGM threads). Also it needs a temperature compensated charger at the very least.

In summary AGMs have advantages that do not transfer usefully to boats and disadvantages that do. Replace them with good quality accessible LA. If you insist on AGM, all your charging sources must remain within the manufactures specs. This means smart chargers on alternators. Solars and mains chargers