Batteries and charging

[prv]

OK, this question is inevitably a big can of worms, but I can't decide what to do and maybe chewing it over in the forum will help.

Ariam's snakes' wedding of a battery bay has now been ripped out. Something better than the pair of bog standard 60Ah car batteries she came with is clearly indicated.

The space is a bit of an awkward shape, made worse by the fact that cables and hoses emerge through the base of it in annoying but immovable locations - but I want to pack as much battery into it as possible. I've determined that the best way to do this is with three 110Ah Red Flash Deep Cycle batteries from DMS Tech, stood on end (DMS confirm this orientation is acceptable). There is just space left in the bay to also fit a small Red Flash High Rate to start the engine. I'm not violently anti-flooded-lead-acid, but they can't be stood on end to fit the space and the non-spill, fit-and-forget nature of the AGMs is attractive. I don't have much space for acid-proof inner boxes and the like.

Charging will mostly be from the engine, a D1-30 with a 115 amp alternator. According to the manual (I've not measured) it's regulated at 14.2 volts. I'll fit a mains charger as well, but we don't currently have permanent power at our home berth so this will mostly be used when visiting marinas elsewhere (and I often prefer to anchor).

Obviously I want to pack as much power into the batteries as possible in a short engine run down the river.

DMS don't really publish full data on their batteries (in an email I asked for more information but not much was forthcoming). In the photo on their website it can be seen that the battery has the following printed on it:

Charging (Constant voltage)
Float Charge: 13.6v - 13.8/25ºC
Cycle Charge: 14.5v - 14.9/25ºC

One piece of information that they did offer was "the voltage applied to one of our batteries should not exceed 13.8V when it is fully charged in order to avoid gassing". Obviously in a sealed AGM where you can't replace the water, gassing = damage.

Those are the facts. Now, how do we synthesise them into an effective charging system?

My natural leaning is towards a voltage-sensitive relay (or the Smartbank equivalent). Gibbo is persuasive when he argues that fancy chargers are not necessary when you have a modern alternator that already charges at over 14 volts (they were useful in the past when alternator regulators were set lower than that). However, DMS advise against this on the grounds that the engine battery will be overcharged while filling up the service bank. That said, I think they're missing the point anyway in that the voltage seen by the engine battery (and the service battery, come to that) will be 14.2 volts regardless of what phase of charge anything is in, because that's what the alternator is regulated to. So if I were motoring across a windless Channel, once I'd filled the service bank I'd be overcharging (by their standards) all four batteries, with my 14.2v alternator.

DMS (or at least the individual I exchanged emails with) didn't really seem to know much about the small sailing boat electrical environment, but they were very keen on smart chargers, saying that even modern cars essentially have smart chargers controlling their alternators. So I guess in our context that means something like the Sterling Alternator to Battery Charger. Claims of recharging the battery five times quicker (than what? A hamster on a wheel?) are attractive, if not wholly believable. But once that bulk charging is done, my understanding is that the A2B doesn't actually control the float voltage, it just turns off its boosting and passes through whatever the alternator is producing. Which DMS assert will kill their batteries. I filled in Sterling's "email" contact form asking for advice, and got sweet FA back.

Is the Volvo alternator simply incompatible with AGM batteries?

I know we have a couple of people with deep battery knowledge on this forum; I hope they will see this and comment.

Whatever I say I know everyone else will chip in their 2 penn'orth anyway

Pete

 

[William_H]

Yes quite simply the charge voltage as regulated by the alternator regulator is a compromise. Higher voltage gives more current in for the short engine run. However on a long engine run thios can overcharge and boil dry the batteries. Hence a regulator which can charge at high voltage then reduce to the float voltage is recommended.
This can be the alternator reglator type which will protect your engine battery and service battery because using a VSR they are all in parallel so effectively one battery
If you use an alternator to battery charger then the service batteries will be well charged and protected but the engine start battery will be susceptible to overcharge at 14.2 volts.
if you fitted a diode type charge splitter you end up with a .7 or more volt drop in the alternator charge which will certainly protect your batteries from overcharge but very much limit the refill charge you need in a short engine run after some weeks inactivity.
Yes a regulated (smart) charger charging at higher voltage will recharge a low battery faster than a normal charge voltage alternator. I can't imagine 5 times as fast bu perhaps twicve as fast under some circumstances. The thing is that a large bank of batteries (or high capacity battery) will naturally take more charge at a lower charge voltage than a smaller bank. So charge current could be limited by the alternator capability anyway. (not likely to be near the 115 amp rating of the alternator but stilla fair bit)

So I can't suggest an obvious solution apart from fitting a smart alternator regulator to fast charge and protect all batteries.
A cheap solution might be to fit a large silicon diode in the alternator output line which will reduce charge voltage so make all batteries very safe. (or fit a diode splitter) then fit a switch where you can bypass the diode(s) to give full (fast ) charge to the batteries when just doing a short engine run. However you must remember to open the switch after perahps 30 mins or you will boil the batteries on a long run.
good luck olewill

 

[prv]

I forgot to mention that the alternator is battery-sensed, although that doesn't directly relate to your answer.

My concern about the "smart" charger - at least the Sterling one - is that it doesn't actually lower the float voltage to a sensible float level. It just stops boosting it. I don't know much about the regulators that you open up the alternator in order to fit, but my understanding is that they generally augment, rather than replace, the original one. So when the "smart" regulator thinks it's time to float, will it just hand over to the (too keen) basic one?

I don't want anything that involves manual switching. It seems like a retrograde step when everything else I'm fitting is designed to make things effortless - and one day someone will forget it and ruin hundreds of pounds worth of battery.

Pete

 

[William_H]

I am pretty sure that the alternator to battery smart chargers will not let full charge of the alternator into the battery. They have internal losses which mean that they have full control of the output voltage to the domestic batteries. ie even with 14.2 volts in the float will only be around 13.75. Check with the makers. However that will not help your engine battery connected to the alternator at 14.2 volts.
Yes it is conceivable that the alternator regulator will only boost alternator output but not reduce it lower than that voltage of the alternaor regulator unless the original alternator regulaor was disconnected. This should be your direction of enquirey to makers if you go down that path. good luck olewill

 

[Plevier]

I've determined that the best way to do this is with three 110Ah Red Flash Deep Cycle batteries from DMS Tech, stood on end (DMS confirm this orientation is acceptable).

Just double check on that. It depends on the layout within the battery. If you have the plate stack horizontal the weight may squash the bottom end squeezing the glass mat and upsetting the acid distribution. This is critical in AGM batteries. They are not saturated (typically 95%).
If the terminals are at opposite ends of the battery it means the plates run across the case and you should not stand it on end i.e. one terminal at the bottom and one at the top. You can put it on its side.
If both terminals are at the same end then the plates run along the case and you can put it on end but not on its side.
I can't see from the data sheet which way the 110Ah one is configured, but terminals at opposite ends is much more common on batteries of this size.

 

[pvb]

But once that bulk charging is done, my understanding is that the A2B doesn't actually control the float voltage, it just turns off its boosting and passes through whatever the alternator is producing.

That's not my understanding of the A-to-B charger. According to the Sterling manual, it does drop the voltage to a float level of 13-6-13.8v. The start battery output however is simply the same as the alternator voltage.

I'm not convinced that constant charging at 14.2v will wreck an AGM battery - after all, AGM batteries are now being fitted to cars, which often have alternators regulated at 14.4v.

 

[Buck Turgidson]

My first question would be do you really need a separate starter battery? With 3 big AGMs in parallel you have loads of cranking amps. Doing away with the separate battery will simplify the charging system and an automatic low voltage cutout can be used to ensure you have the oomf to start the engine when the batteries get low.
There are plenty of alternator regulators around now which will work in 2/3 or 4 steps to keep your batteries in good health. Mastervolt make some very interesting products as do Sterling and others.

 

[neil1967]

Pete

Have you looked at the optima range of AGM batteries - red top for starting, yellow top for domestic (I've not used yellow)? These are spiral wound and can be mounted in any position. They can be charged up to 15v without gassing or damage. I have a redtop starter battery, which is charged from the alternator and an old sterling alternator controller, through a no-loss splitter that also charges 400AH of Trojan wet acid batteries at up to 14.8v, with a float at 14.2v (from memory) . Additionally, when on mains the red top is charged from a dolphin 30A charger on a lead-acid setting (to suit the Trojans). I've only done one season in this configuration, but all seems well and the wet acid charging regime is within the optima charging specification. I think they are slightly larger than the red flash though.

Neil

 

[jac]

Think you're wrong re the sterling A to B. I have just installed one and 3 key points for me.

1. It can be set for different types of battery, so wet batteries have different charging profile to AGM. Just need to review the float and bulk phases profiles and ensure they match your battery.

2. It does drop to float voltage - in the manual it has some very pretty graphs of what happens to volts and current over the charging cycle

3. The boost only goes to domestic. The starter gets an unboosted charge first for about 3 minutes to replace what starting may have had, then the A to B goes to work on the domestic, switching back to the starter as required. (Every 20 mins iirc)

Think if you get one you would need to set up as AGM exide spec not AGM US spec.
Exide spec specified 14.4v then dropping to 13.8
US spec is only 14.2 v then dropping to 13.5 float.

It should work fine with your alternator - it specifies 13.8 to 14.4. The alarms go off and it trips over 15v and you have to do some resetting if voltage is below 13.8 but your alt seems nicely in the normal range!!

 

[RobbieW]

I'd go with jac, he's installed a Sterling A2B - I've only read the marketing stuff. It certainly looks as if it does the same job as a 3 or 4 stage mains charger, I guess it must dump voltage it doesnt need and it appears to be the only 'alternator controller' on the market that does this - EDIT actually because its not an alternator controller but a battery charger that happens to use the alternator output as its feed. I've thought about replacing the existing Adverc with one but not quite got round to it.

fwiw, I have a not dissimilar set up to yours in that I chose DMS Red Flash house batteries. My engine battery, currently an Optima Red Top, needs replacing this year. Long story short; I'm not replacing the splitter diode that was too small, I'm going to wire the alternator direct to the house batteries. To charge the engine battery, I'll use the emergency changover switch for 1/2 hour as required. This idea came from a paper I found through the CA; it addresses both KISS and the thought of overcharging the engine battery.

 

[prv]

I am pretty sure that the alternator to battery smart chargers will not let full charge of the alternator into the battery. They have internal losses which mean that they have full control of the output voltage to the domestic batteries. ie even with 14.2 volts in the float will only be around 13.75. Check with the makers.

I tried. They didn't respond.

However that will not help your engine battery connected to the alternator at 14.2 volts.

The Sterling blurb says there's a diode in the starter path, so that will at least cut the voltage a little.

Pete

 

[prv]

Just double check on that. It depends on the layout within the battery. If you have the plate stack horizontal the weight may squash the bottom end squeezing the glass mat and upsetting the acid distribution. This is critical in AGM batteries. They are not saturated (typically 95%).
If the terminals are at opposite ends of the battery it means the plates run across the case and you should not stand it on end i.e. one terminal at the bottom and one at the top. You can put it on its side.
If both terminals are at the same end then the plates run along the case and you can put it on end but not on its side.
I can't see from the data sheet which way the 110Ah one is configured, but terminals at opposite ends is much more common on batteries of this size.

Thanks for this. I have an email from DMS saying that on end is ok - I was very specific about differentiating between "end" and "side" - but there's always the possibility of the person answering email that day getting it wrong. Not sure how to address that except to contact them again (maybe phone) and hope I get someone else. The 110Ah battery (according to the photo, anyway) has the terminals at opposite ends.

Pete

 

[prv]

Doing away with the separate battery will simplify the charging system and an automatic low voltage cutout can be used to ensure you have the oomf to start the engine when the batteries get low.

I don't much fancy the idea of everything - GPS, nav lights, autopilot, VHF, internal lights, etc - suddenly cutting out one night in the middle of the Channel.

Pete

 

[prv]

Have you looked at the optima range of AGM batteries - red top for starting, yellow top for domestic (I've not used yellow)? These are spiral wound and can be mounted in any position. They can be charged up to 15v without gassing or damage.

I'll have a look. I spent many many hours in the autumn trawling through battery specs, although originally (till I got some help with the cost from my co-owner ) a lot of that was looking at wet batteries. But most of what I found wouldn't quite fit - or rather, with the maximum number of units that fitted, the amount of wasted space was high and the number of amp-hours was low. The Red Flash ones seemed to be a marginally different size that just cleared some of the hoses and allowed a different configuration. But I may not have checked the Optima range. Certainly if they can tolerate a high float voltage then that will be useful.

Thanks.

Pete

 

[Plevier]

Thanks for this. I have an email from DMS saying that on end is ok - I was very specific about differentiating between "end" and "side" - but there's always the possibility of the person answering email that day getting it wrong. Not sure how to address that except to contact them again (maybe phone) and hope I get someone else. The 110Ah battery (according to the photo, anyway) has the terminals at opposite ends.

Pete

Try asking them if they have considered this particular point, particularly for batteries that won't be taken out for a long time.
DMS are a competent outfit but this is an easily overlooked point. If they still insist it's OK, fair enough, maybe there is something clever in the design, but it certainly mattered when I was involved in AGM batteries, admittedly a good many years ago now but sometimes things have to be learned again. (Boring old fart mode )
I don't know who make that particular range of batteries for DMS to check unfortunately.

 

[prv]

2. It does drop to float voltage

Is that with an old 13.8v alternator, or a newer 14.2 / 14.4 one?

in the manual it has some very pretty graphs of what happens to volts and current over the charging cycle

...with what input voltage?

Pete

 

[prv]

Have you looked at the optima range of AGM batteries - red top for starting, yellow top for domestic (I've not used yellow)? These are spiral wound and can be mounted in any position. They can be charged up to 15v without gassing or damage.

I've just checked the specs. They list a float voltage of 13.8, same as the DMS batteries.

Pete

 

[Buck Turgidson]

I don't much fancy the idea of everything - GPS, nav lights, autopilot, VHF, internal lights, etc - suddenly cutting out one night in the middle of the Channel.

Pete

They would anyway if you let your house bank get low enough. It's no different except the time to turn on the engine is a little earlier. On the plus side simpler electrical system and you're not lugging around a starter battery. The voltage cutout is the safety system for when the user fails to monitor the voltage closely. You could just as well have an alarm rather than a cutout.

 

[halcyon]

I've just checked the specs. They list a float voltage of 13.8, same as the DMS batteries.

Pete

Float voltage is a permanent on charge voltage, charging from the engine will not need this as running time is limited by fuel tank.

The other thing to remember is that the voltage you see when charging from the alternator is not DC, it is half a sine wave, the top section above the DC voltage is the bit that charges the battery. So say the DC meter says 14.2 - 4 volt, the peak measured on a scope can be 15.5 - 16 volt, hence the high gassing with high levels of alternator boost.

It's the pulse above the DC voltage, that allowed us to fully charge a standard flooded battery with a mains charger running 14.3 volt.

Running the boat from a single bank with low volt cutout is not new, goes back to 1982, the unit also had a LED voltage monitoring and audio drop-out option. The reason back then for pushing a separate engine start battery was low voltage and spikes during engine start, causing problems to nav equip.

Brian

 

[jac]

Is that with an old 13.8v alternator, or a newer 14.2 / 14.4 one?



...with what input voltage?

Pete

Either. It will work with a voltage up to 15v before it cuts out. As robbiew says, it dumps extra voltage, I believe as heat as it has 3 fans in it but I didn't design it so not sure on the details.

You're welcome to come and have a look if you want. (If it helps) am at Deacons most weekends.