I'm running 2 AGMs. Start and house. Start is fine. House was replaced less than a year ago and I suspect it is already knackered.

House normally gets a reasonable discharge when sailing - say max 50% since I've been running the autopilot.

But.... It is only ever charged off the alternator (I religiously switch to "ALL" when the engine is on).

I tried to charge it with the Mains charger in AGM mode tonight and it's claiming to be full, which is bull****.

Is this why people recommend those redarc charge controllers? Have I knackered it?

Probably not. Buy a cheap modern Chinese pulse charger. Take the battery home and charge it overnight. Fit a solar panel to trickle charge. I run two batteries with two separate solar panels and regs. I don't use the alternator at all though I do have a switch on the Fields wire so I can charge the batteries at night with the motor if required.
My charger was about $25 from aliexexpress.

Charger is a C-tek M45.
More digging required I think.

Lead acid batteries sulphate when they discharge, recharging them reverses the sulphation. Because they accept charge at lower rates as they become full it is difficult to recharge them to completely full just using an alternator or generator. The last 5% of charge could take hours of motoring to top off the battery. Not practical to do

However to reverse all the sulphation they need to be fully charged. If they are not fully charged after every use, over time, the sulphation can crystalise and become impossible to reverse. That diminishes the capacity of the battery. Now with a diminished capacity the alternator still struggles to top off the last 5% of the reduced capacity which doesn't reverse the new sulphation, that further reduces the capacity and on it goes until the battery is stuffed.

So Lead acid needs to be fully recharged after every use, if you cannot do it with an alternator or generator which you can't, you need another charging source to top off the batteries.

Your start battery is probably fine because it is getting fully charged but the house bank is never getting fully charged and the above has happened.

Certain brands of lead acid batteries can be equalised, lifeline and Trojan to name a couple. Equalising is basically a overcharging procedure that blasts the sulphate crystals away restoring the batteries capacity. You need to refer to manufacturers specs to see if its possible and what the procedure is.

Thanks for the pointers breezers, my knowledge is quite out of date.

I disconnected the house battery and plugged in my Repco 2.5A mains charger tonight direct to the terminals. It's not an AGM model but at least, having cleared the path so to speak, it is a known configuration. Will see if it's knackered tomorrow.

I think in the short term I'll keep the 1/2/both/off switch to give me the flexibility to crank the motor from the house battery in a pinch, however under normal operation it will only be in either 1 (starting or charging the start battery) or Off. No normal charging the house battery with the alternator. I'll need a new separate isolator for the house circuit but this will enable me to re-wire the instruments straight away without screwing around with the alternator/cranking circuit.

I'll (re)wire the mains charger to the house battery and charge the house battery every time I leave it in the marina. I can do this straight away.

Then I'll get some kind of VCR/Charge controller to charge the house battery from the alternator only when there's excess power. I might do this at the same time as adding solar.

Thoughts?

Jon, with all the tec around today you're going the right way.imho 2 individual systems house solar/wind or whatever tickles your fancy with an onboard dc to dc charger keep the house battery in the useable range. A shunt to monitor the amps used & and generated is on my shopping list next time I get dc electricly motivated

p3p4p5 said..
I have that CTEK Charger and I have used it on all sorts of batteries right down to 7ah and it never damaged a battery.

Why dont you pull the multimeter out and check each batter individually. You will At least know the state of charge of each battery.

I would separately charge each battery in the "Condition Mode" on the CTEK and then combine them. Then check the terminal voltage after a recondition charge cycle.

One Battery could have a damaged cell and all that you are doing is putting the batteries in parallel which will read the voltage of the good battery which is above the one with the damaged cell. You essentially fooling the charger into thinking that the batteries are charged because the charge state is indicated by the terminal voltage of the battery with the highest terminal voltage. The multimeter will give you a instant answer if one battery is under charged or faulty.

I think the problem is that the Ctek is not wired to the house battery in isolation. In fact I haven't completely figured out how it is wired yet.

So the house battery never gets a proper charge from the mains charger - hence the post title.

Ramona said..

cammd said..
Lead acid batteries sulphate when they discharge, recharging them reverses the sulphation. Because they accept charge at lower rates as they become full it is difficult to recharge them to completely full just using an alternator or generator. The last 5% of charge could take hours of motoring to top off the battery. Not practical to do

However to reverse all the sulphation they need to be fully charged. If they are not fully charged after every use, over time, the sulphation can crystalise and become impossible to reverse. That diminishes the capacity of the battery. Now with a diminished capacity the alternator still struggles to top off the last 5% of the reduced capacity which doesn't reverse the new sulphation, that further reduces the capacity and on it goes until the battery is stuffed.

So Lead acid needs to be fully recharged after every use, if you cannot do it with an alternator or generator which you can't, you need another charging source to top off the batteries.

Your start battery is probably fine because it is getting fully charged but the house bank is never getting fully charged and the above has happened.

Certain brands of lead acid batteries can be equalised, lifeline and Trojan to name a couple. Equalising is basically a overcharging procedure that blasts the sulphate crystals away restoring the batteries capacity. You need to refer to manufacturers specs to see if its possible and what the procedure is.

These repair batteries. Bit noisy but they work as advertised.

www.aliexpress.com/item/1005008487547964.html?spm=a2g0o.productlist.main.35.53f7kpR5kpR5Tj&algo_pvid=d97cd58a-2284-4028-85a3-5fe692aeaa09&algo_exp_id=d97cd58a-2284-4028-85a3-5fe692aeaa09-17&pdp_ext_f=%7B%22order%22%3A%2291%22%2C%22eval%22%3A%221%22%7D&pdp_npi=4%40dis%21AUD%2121.41%2118.99%21%21%2197.76%2186.71%21%4021015b7d17447538400681794eb102%2112000045857590034%21sea%21AU%21753417160%21X&curPageLogUid=k7EYYV7VynO3&utparam-url=scene%3Asearch%7Cquery_from%3A

That's an interesting charger thingy. I've been adding phosphoric acid to flooded lead acid, it's supposed to extend the life of the battery by removing sulphate build up. Bit hard to tell if it works because some scum bag stole them.

OK, first proper sail today with the mast back in after pretty much a complete re-wire of the instruments.

Pulled the fastnet bus apart and re-did it.

Got a length of nice thick marine power cable and ran a dedicated 0 volt for the instruments.

Then I ran a length of 15A cable from the main isolator straight to the power input for the autopilot drive.

No low voltage warnings. No weird **** with the instruments (which was happening before). Ran the pilot for about 6 hours and the battery still showed 12.4V.

Also I didn't charge the house battery when I ran the motor. Just let the alternator charge the cranking battery and left the mains charger doing it's thing with the house battery when I tied up.

So all's well that ends well. Thanks for the pointers and the suggestion to persevere with the battery instead of wasting money on a new one.