batteries - Maximum charging current

[zefender]

I'm putting together my daily amp hours requirement. If this were to be, say 200 amp hours, I'd need to charge at the rate of 8 amps or so to replenish the batteries every day - unless I'm missing something here. Does anyone know what maximum charge batteries can cope with before 'boiling over? I have a regulator and presumably this limits the inbound current to keep the batteries in condition.

Also, does any one know where I could buy an amphours counter for the battery bank?

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[Talbot]

Different battery types will accept different charge rates (Carbon Fibre reinforced and gel seem to be the best at this, and larger banks will accept a higher charge rate than small banks. A standard regulator is not designed to get the maximum charge into a battery as fast as possible, to do that you need to add a stepped charge alternator regulator from adverc or stirling. These work in a similar manner to the stepped mains chargers where they have the ability to push in max power when needed and a floating charge where required.

There are several devices that will tell you charge in/out. assuming you have two battery banks, then look at the Link 200 or BEP.

Recommend a long talk to <A target="_blank" HREF=http://www.barden-uk.com/>Barden Batteries</A>

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[snowleopard]

maximum charging current is generally taken as 1/3 of the battery capacity, e.g. a 75AH battery can be charged at up to 25A.

the best known amp-hour meter is the Link 10 battery computer which reads amps, volts, amp hours and time to discharge.

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[Robin]

200 amps per day on your boat would be very high usage and 8A charging is unbelievably low so maybe you meant 80A?

Firstly remember you shouldn't discharge a battery beyond 50% or it won't last long, so your total battery capacity is really only half what it says on the box. Secondly with smart regulators (either on alternaor or shorepower mains charger) you can pretty much throw any amount of amps at the battery until it is about 80% charged, then the charge has to reduce to avoid gassing and 'boiling' the battery.

I think we need more information on what you are trying to achieve.

Robin

<hr width=100% size=1><font size=1>Sermons from my pulpit are with tongue firmly in cheek and come with no warranty!</font size=1>

 

[Anonymous]

RE Ahr counter

I have just installed the BEP. Too early to give proper feedback but we liveaboard and if anyone asks in a month or so I'll post an update. My present feeling is very positive indeed, but do ask for an update, I only got it working last night!

As I write, I am carrying out a discharge test on our main house battery which would be impossible without such a device, while living aboard, since the load necessarily changes.

Meanwhile, the bilge pump monitor, which is an integral function of the BEP, is brilliant. It tells you the number of times the bilge pump has operated and the total pump running time in mins and seconds, resettable. I've actually got my weepage (stern tube and rudder gland mainly) to such a low level that the pump doesn't need to come on unless one of the shower trays overflows so any unexpected pump operation will be worth investigating. Well worth having for safety and peace of mind.

One final point - you do need to install these monitors with care. No bodges or lash-ups will do because if you put too much resistance in the boat's battery supply you will have nothing but electrical problems for ever more - serious hell, believe me. Also, the output from the shunt (the current monitoring device) is very low (millivolts) and you must follow the manufacturer's instructions. If, like me, you don't wish to afford overall screened twisted pair and prefer to make your own twisted pair with a drill or electric screwdriver then you can use a tightly-twisted pair for the signal, with the earth return running loose alongside. Seems to work with my SSB transmitting on full power, when modulated normally, but it reads a silly, high, current when I deliberately overmodulate it. I can live with that!

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[zefender]

I know useage seems high but considering the following, it's entirely plausible, if a bit scary:

Fridge - 4a - 20 hours - 80 amp hours
Autohelm - 3.5amp - 24 hours - 84 amp hours
tri-light - 2 amp - 12 hours - 24 amp hours
Interior lights (3) - 5 amps - 5 hours - 25 amp hours

... I appreciate the above may not be entirely accurate, but I think 200 will not be wildly out. Alastair Buchan, in his book ' Sailing an Atlantic Circuit', talks about his power budget being 110 hours - and he had windvane steering and no fridge!

My 8 amp was my estimate of likely charging per hour. So, in 24, I'd be achieving 192.

If I assume a 80w solar, this should (assuming 70% efficiency and 10 hours sunlight per day) give me 46 amp hours. A duogen (in water mode) may give another 140 or so. The total of both of these is 186 - which is near my budget.

So, my worry was whether 8 amps going into a battery would boil it or whether it would be OK. Given that it seems, from other replies, they will be able to cope with a far bigger charge, this doesn't seem to be a worry. But I'm still left with something of a concern about how to produce a reliable 200 amp hours a day!

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[bedouin]

As an aside, if you are expecting your fridge compressor to be operating 20 hours out of every 24 then that sounds uncomfortable to me - perhaps you should consider more insulation, or a more efficient heat exchanger?

Also note that if you have charging devices operating most of the time then not every Ah you require has to go through the battery bank, so the peak charging rate is less important.

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[zefender]

Much of what I've read suggests that 16 hours working seems more normal. I've actually no idea (yet) how many hours a day mine needs to operate for - but It'll obviously be for more hours in warmer climes. I suspect though that power peaks at first, as the compressor kicks in, before settling down - and thus the estimate of hourly consumption is an average.

I take your point about the real usage/charging rates though I suspect that at night, when power consumption will be less, there will be more charge than use, if you know what I mean - albeit with no solar power natch

<hr width=100% size=1><P ID="edit"><FONT SIZE=-1>Edited by zefender on 02/11/2004 12:04 (server time).</FONT></P>

 

[Anonymous]

>>Much of what I've read suggests that 16 hours working seems more normal. I've actually no idea (yet) how many hours a day mine needs to operate for - but It'll obviously be for more hours in warmer climes.<<

I'm in a similar position. We have a keel-cooled fridge and at the moment we are using it as a deep-freeze in the bottom section and fridge on top. It seems to be running most of the time. Elsewhere I have written about the BEP battery monitor which also has a bilge pump monitor/log. I am thinking of temporarily disconnecting the bilge pump signal and taking the fridge compressor signal to the BEP monitor so that I can get the total number of cycles and the total run time. If I do this, I will probably wire it via a toggle switch so that I can always change the function over as circumstances change. You sound as though you have a good general understanding of electrics and you might also benefit from a monitor such as the BEP.

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[zefender]

"You sound as though you have a good general understanding of electrics "

Very kind - completely wrong of course, but very kind

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[pvb]

Amphours counter...

You asked where you could buy an amphours counter. Lots of better chandlers stock the Link 10, or you could talk to <A target="_blank" HREF=http://www.merlinequipment.com/prod_area.cfm?area_id=40&ind_id=1>Merlin Equipment</A> who sell both the Link range and the BEP range.

I've had a Link 10 for years, and it gives very useful information. It's also available in a number of re-badged versions as a Mastervolt product, an E-meter, etc. The Link 20 will monitor 2 battery banks, but for most people I don't think it's necessary to monitor the engine start battery as long as it's properly isolated from the domestic bank. The BEP DCM600 will monitor up to 3 banks (or 2 plus a bilge pump). Although I'm happy with the Link 10, if I was buying a monitor today I'd go for the DCM600 because it has better graphics. Both the Link and BEP monitors are programmed to use Peukert's Exponent in their calculations - an essential feature if the data is to be accurate. Note also that it's important with any of these monitors to set them up properly initially, according to your battery bank size and type.

One thing you'll find when you get a battery monitor is that there are all sorts of little power drains which you may not have thought about before. Although you're approaching your power usage calculation very sensibly, you haven't allowed anything for instruments, gauges, GPS, VHF, radar, CD player, etc, etc. These are very real consumers of power, and it all adds up!

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[Talbot]

One way to cut down on your budget is to use an LED tricolour light. Most efficient is from <A target="_blank" HREF=http://www.deepcreekdesign.com/tristarpage.html>Deep Creek</A>and should reduce your estimated use by abt 15 amp/hrs/day.
Your biggest loss seems to be the Fridge Freezer. This estimate would seem to be very far out on what I would expect (and reports from other boats). Therefore there is either something wrong with your system, or the insulation is totally inadequate. I would strongly suggest that you should investigate this. Possibly you are running to small an evaporator, or too small a plate, or you have lost some of the refrigerant. Most reports talk abt a 50% duty cycle.

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[pvb]

Sorry, correction....

Sorry, folks, I didn't explain that very well, and it's too late for me to edit the post. The Link 20 has a dual shunt and so will monitor 2 battery banks separately and simultaneously, including Ah measurements on both banks. The BEP DCM600 (like the Link 10) only has a single shunt and so can only show Ah data for one battery bank. But it can show voltage readings for up to 3 banks (or 2 plus a bilge pump monitor).

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[zefender]

Re: Amphours counter...

Thanks for the info - I'll follow them up.

You're right about the need for a full list of kit to scrtach away on the overall consumption. I was just using some in my post to illustrate the point that it's quite easy to need 200 amp hours/day. Even in standby mode the radar takes up quite a bit, as well as the PC, water/shower pumps etc. Looks like my nice new big LCD display won't get much of a look in for those DVD evenings we'd planned!



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[zefender]

I've seen details of the LED tri-light. Although not strictly compliant with the regs, it does seem very tempting and a great way of saving a lot of power. I read of one 'test' that seems to reckon that it didn't have the required visibility - but was close.

Interior LEDs are a possibility though. I understand that there are new 10 LED ones available now which are a bit brighter than the existing alternatives. So this might be a possibility.

As far as the fridge is concerned, maybe my estimate is far too pessimistic - I hope it is! I need to get out the manual and check the details to be sure. When I get a better fix on usage overall, I'll post the details. But I do suspect that 200 is not that wide of the mark (sadly!)

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[Robin]

The fridge consumption should be way less than your figure if the insulation is good enough. It may be possible to add more insulation or even to build an 'inner' lining to the fridge with extra insulation between it and the original. The pilot should average nearer half your quoted figure if it is an inboard version. So this will help your daily figure but there are others you haven't listed that will hurt, like instruments, vhf, pressure water pump etc.

If you then look at the replace amps side of the equation there are lots of options:-

Consider a towed water generator at sea. This will cover the times when the pilot and nav lts are in use and hopefully have some extra as well.

Solar panels. We have a fixed 75W one on our gantry and a 'roving' one we put out on deck when needed which is a whopping 110W. Wiring is arranged so that we can have either or both charging either or both of our two main battery banks.

Wind generator. We have a big one, an Aerogen 6 that puts out a lot of amps and feeds any or all of our 3 battery banks as needed. via a splitter/regulator.

Shorepower. A high powered smart charger will help when AC is available. We have a 40A one with a control that allows power reduction either to run from low power shore outlets or from a small petrol generator.

Engine alternator(s) We have 2 alternators each with smart regulators, one charges the instruments/pilot/lights battery as well as the engine one, the other charges the fridge/SSB/more lights/#2 plotter etc. Each alternator has a max output of 90A. At least if we must motor we are stocking up on amps.

I have a simple spreadsheet that allows 'what if' interrogation to see the effects of reductions in usage or increases in charging, if it helps PM me an I'll e-mail a copy.

Robin

<hr width=100% size=1><font size=1>Sermons from my pulpit are with tongue firmly in cheek and come with no warranty!</font size=1>

 

[zefender]

Thanks - see pm

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[dickh]

Your fridge rating looks high. Assuming it has a Danfoss or similar compressor, these usually pull about 4 amps to get down to temperature then about 1 amp per hour a thereafter. Autohelm also looks to be on the high side but not having the figures may be accurate.

<hr width=100% size=1>dickh
I'd rather be sailing... /forums/images/icons/smile.gif

 

[Evadne]

Re interior lighting, have you considered oil lamps for ambient with electrics for reading etc.? I find going onto someone else's boat at night that the lighting is very cold and harsh compared to our little paraffin-powered glow-worms. If you're reading or washing up or whatever then you need more light but you can switch them off again afterwards. Even saving one electric light would cut quite a bit from your amperage budget.

I've not used interior LED lights but if they are anything like the LED torches I wouldn't have them. Very bright to look at, but a weird colour that doesn't seem to reflect from anything. Or maybe its my eyesight deteriorating after years of straining throught the dim glow of oil lamps?

Re. pessimistic estimates, the autohelm seems a bit high as well to my eyes. If the boat is passably well balanced or you're motoring then you would hope the motor is not running at full power continuously. It would be interesting to log the consumption over varying conditions to see just how much they do use.


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[zefender]

I need to check the fridge rating but your estimate is useful. The Autohelm (ST600+) uses 1.5 - 3 amps according to the manual I've just checked. I know that in a following sea, it works at its hardest so I wouldn't be surprised to see a 3 amp figure emerging and its most appropriate I think for a planned Trade Winds transat.


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