12v battery or do i go 6v

[nicknorman]

1 hour ago, Mike the Boilerman said:

 

 

Not that much bigger. Approaching 100% SoC represents a really big risk of wrecking the set. If you hit 100% and charging continues (how confident are you the charger will know, during charging?) then the batteries will probably be wrecked. So charging to 80% SoC is prudent. Maybe 90% if you are sure you know the SoC whilst charging and feel brave. And at the other end discharging to say 20% then starting to charge means you are using only 60% of capacity. 

 

The other approach is to hand it all over to say Victron, RELiON or Valence and pray their integrated management actually works. Every single time ever. 

 

 

 

Oh and another reason not to charge to 90% or more is these cells don't like being stored at over 80%. Not sure why not or what happens if you do. 

It is not that much bigger if you only consider AH and only charge to 80%. However don't forget that a LI battery at 50% SoC has a higher voltage than a LA one, especially under significant load, thus the WH advantage is much more than the AH advantage. Many devices are constant power devices - fridges, regulated LED lights, anything powered by an inverter, switch mode device chargers, water pumps to a slightly less extent - and thus will take more current to achieve the same thing if the voltage is lower. A LI battery under modest load will give 12.7v or more. A LA battery under the same conditions will give under 12v. An added effect is that with the higher current required from the LA battery to do the same work, one gets more voltage drop and hence more power lost in the wiring.

 

As to operating above 80% SoC yes of course one would have to have a well designed system to ensure no overcharge, but that is something I'm sure DMR is quite capable of.  Storage at high SoC is to be avoided, but wouldn't be an issue for a live aboard - discharging will start as soon as charging has finished. The only thing to be avoided would be to leave the batteries at 100%SoC having turned off the master and gone on holiday for a month, or for a leisure user, leaving the boat in the marina for months over the winter with the batteries full.

[Tony Brooks]

1 hour ago, Neil2 said:

The last time there was a long thread on this I did a back of an envelope calculation based on members experiences with cheap batteries vs my experience with Trojans and to be honest it seemed to be a six and two threes. 

 

But these days I suspect buying cheap and accepting you might have to replace more often makes more sense financially.  I think now we have cheap solar the problems of keeping batteries charged tilts the seesaw towards cheapos. And if you only boat during the "season" I think buying cheap wins hands down.    

 

Personally next time around I'd be tempted to go down the 6v route but only because they are easier to manhandle and I've never had a boat where the batteries were easily accessible (is there such a boat?)  

Yes, mine. Ex hire with 3 x 110Ah or taller through a hole in the  cruiser stern deck. Just take the board off, disconnect  lift them ut. Downside is it will be a pig to modify for more batteries or anther case style/size.

 

However I tend to agree with your second paragraph. 3 x 110 Ah Exide leisures fitted June 2003 and still performing as we require. Admittedly a holiday boat but it is never connected to shore power but does have modest solar. It powers an electric 12V fridge lamps (florescent & LED mainly), Pumps, laptop, TV, car radio-CD player, charging phones, and small inverter to charge idiot Apple stuff with odd charging leads etc. We are now in the sixth year and the only "equalisation" is done by the solar at 14.8V every 30 days (or so the instructions say). Reading what others say about equalising Trojans it woudl mean running a generator and buying a sutably battery charger. I am not sure Trojans are as good as is claimed if you have to keep messing about with equalisation.

[dmr]

2 hours ago, nicknorman said:

But a massive advantage for a live-aboard surely has to be the much faster recharge time - the charge current barely tails off as the battery approaches 100% SoC - and the absence of need for daily charging to ward off sulphation. So it is not just about the cost of the product, it is also about the cost and convenience / nuisance value of daily charging. I wonder how many hours of engine running would be saved per day, times 365 (well OK, times the number of static days) times say 20 years, and what the cost of that is in terms of fuel and engine wear not to mention annoyance.

The more I think about the Lithium vs Trojan decision the more subtle it all becomes.

The better charge characteristic is probably the biggest advantage for me, but then much less important for someone with your style of boating.

(There is no need to charge the batteries daily, if you need to do this then you need more batteries? )

The absence of sulphation and equalisation is also a big advantages.

Lithiums are "clean" whilst wet batteries are always a bit wet and nasty.

No topping up, or forgetting to top up and feeling bad!!!! Lithiums are almost "fit and forget".

 

The faster charge is perhaps not quite as great as it first appears. If I only run the engine every second or third day (in winter) then I need a longish run to get the hot water hot and the washing machine doing its stuff. Also a lot of engine wear is due to start up rather than hours running. A very rough calculation suggests that my engine running hours might drop from about 1100 each year to maybe 900. For boats with a lot of solar the faster charge is less important, especially if the "winter generator" is too small to produce a big charge current.

 

The high cycle life is probably a disadvantage!!!! If I can squeeze 7 years out of the Trojans then that equates to 28 years from Lithiums, thats just too much, they will be obsolete before they wear out, and I am unlikely to be boating in 28 years times anyway (because the canals will be repurposed as cycleways). Lithiums would be more attractive if they had half the cycle life and half the price.

 

I still think Lithium is the way to go, but not just yet. For me I think the main advantage is that I just don't like running my big engine to trickle 15 or 20 amps into the batteries.

 

..............Dave

 

 

[Matt&Jo]

So how do you calculate the size of genny needed for your battery charging....i am intending to fit 500+w of solar and use a small petrol genny (yes i know they are a nuisance and dangerouse) but needs must in the winter......to top up and power my 4 x 110amph battery bank. Sorry if this is blatantly obviouse but fool for 5 mins rather than a fool for buying the wrong genny and all that....

[nicknorman]

2 minutes ago, Matt&Jo said:

So how do you calculate the size of genny needed for your battery charging....i am intending to fit 500+w of solar and use a small petrol genny (yes i know they are a nuisance and dangerouse) but needs must in the winter......to top up and power my 4 x 110amph battery bank. Sorry if this is blatantly obviouse but fool for 5 mins rather than a fool for buying the wrong genny and all that....

No not blantantly obvious. The genny doesn’t charge the batteries directly, but via a charger. So it depends on the size of charger you get. Bigger charger means less running time (but with diminishing returns) but needs bigger genny to run it.

 

Also, for a given continuous rating different gennys have different capabilities to deal with the surge load encountered when the charger is switched on. And some charger present a big surge load, some are “soft start”. Yup, all quite complicated!

 

I’d be inclined to go for a suitcase inverter genny around the 1.5 to 2kw which should have enough margin to run a reasonable charger around 30 or 40 A. But the best way is to copy someone else’ combination of charger and genny that you know will work.

[Matt&Jo]

So i have an inbuilt charger inverter anyway that looks fairly beefy il have to read up and check out its capabilities....all this talk of pure sine wave and it not being pure is hurting my teenie tiny brain........

[MtB]

29 minutes ago, Matt&Jo said:

So i have an inbuilt charger inverter anyway that looks fairly beefy il have to read up and check out its capabilities....all this talk of pure sine wave and it not being pure is hurting my teenie tiny brain........

 

The sining and waving is nothing to do with the battery chargings, so you can stop reading that section.

[Tony Brooks]

1 hour ago, Matt&Jo said:

So i have an inbuilt charger inverter anyway that looks fairly beefy il have to read up and check out its capabilities....all this talk of pure sine wave and it not being pure is hurting my teenie tiny brain........

The pure sine wave bit probably refers to the output of the inverter part BUT some electronic equipment gets very miffed if its fed a waveform that is less a smooth wave than that of mains electricity so to be sure a generator will  drive a charger it really should be a pure sine wave on like most suitcase inverter generators. You may be lucky with a modified sine wave one but its a risk.

 

If the generator you choose can not drive the battery charging part of your inverter because its not powerful enough then you may find the charger part can be adjusted to take a lower power but deliver a lower charge. More head hurting in the instructions I am afraid.

[WotEver]

If you tell us exactly what you have we may be able to advise. 

[Gareth E]

I have a Kipor 770 with 20a Sterling charger. Works for me and the genny is only 11kg so easy to handle and move around. It lives chained to the cruiser deck in the winter, when it's used. In the summer it's drained of fuel including carb etc. and chained inside the cratch. 

[sirweste]

I've a Mastervolt Combi, which has a 100 A charger. At bulk charge me Honda 2 kW genny siiiiiings, but has enough capacity left to also run the fridge.