Battery charger advice please

pragmatist

pragmatist

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We have been meaning to replace our trickle charger for ages and not got round to it. HWMBO has now decided he'd like one for his birthday (today ! so I'm a bit late) and we were about to buy the Sterling 30A (12V). Then we looked at the price of the 40A and wondered about that. Then yesterday we came across a gismo to reduce the power taken by a charger because they can cause some marina systems to trip.

So I'm here to ask advice on :

1) What charger (make and size) should we be buying ?
2) Has anyone every had need of the gismo to reduce the power requirement ?

We have 330Ah batteries (220 for house and 110 for engine starting). Our drain when on mains comes from fridge, lights, instruments.

TIA
Penny
 
You don't get anything for nothing - and that applies in power terms as well. The device to reduce power load in the marina is either an illegal device that alters the power factor of the load (very naughty thing to do and the small print of any electrical distribution network will specifie that you shouldn't do it!) or it reduces the load in such a way that it will turn your 40A charger into a less than 40 A charger.

However, I don't believe that you should be worried about the load. Assuming you go for a 40A charger, even when it is delivering 40A (which it won't do all the time because of the physics and chemistry of the batteries) that makes 480 Watts (40x12). Sterling are switch mode chargers which are fairly efficient, so even allowing for 20% inefficiency we might estimate 600Watts used, which at 240v is only 2.5 Amps. This is not going to be a problem for any shore power connection.

Our experience supports this. When plugged into a 16A connection with immersion heater running and the battery charger going strongly, there is no problem at all. However, if you start plugging kettles or hair dryers in as well, there might be a problem - in which case the easy answer is to turn the immersion heater off for a few minutes!

Some people say rude things about Sterling. We have used a number of their products on several of our boats and have never had any problems. Pay your money and take your choices about which charger to get. The 40A one sounds a good bet to me though!
 
Thanks for the prompt response (you must be sitting at home looking at the weather like us /forums/images/graemlins/frown.gif). The gismo is a Sterling product which does reduce the load and does turn the 40A into less than 40A as you suggest - but sounds as though we don't need it.

Do you know of any good reason not to go for the 40A rather than the 30A ? For about an extra £50 I would have thought it would add a bit of future-proofing (whoever reduces their electrical requirements ?!) if there are no downsides.

Penny
 
No I can't think of any reason not to go for the 40A. The charger will act as a power supply as well as a bettery charger, and so you effectively run all your 12v off the mains as you are charging. A little extra power available won't do you any harm.

And yes, we would have been on the boat if I wan't looking at a very wet Dartmoor scene out of the window!
 
I too replaced my old charger (a Newmar), with a Sterling and have had no problems with it whatsoever. My battery banks are about the same size as yours and I find the 20A version keeps up with me living aboard, (but I do have twin engines so plenty of charging available when i'm out and about) so the 40A should keep you future proofed for some time. Some people don't seem to like Sterling kit, but I find it refreshingly "honest". Unfortunately, I'm about to go to work in this weather! Wish I could look out on it instead of being in it!
 
I think what he means (always a dangerous thing to say!) is that Mr Sterling doesn't suffer fools gladly. If you phone him with what he thinks is a numpty question he can be a bit prickly. Also his manuals as supplied look as thought they have been autotranslated from Serbocroat via Flemish. The products work though!
 
We have a 360Ah service bank and our 30A Sterling charger has no problems keeping it full on an overnight charge. 40A would allow it to charge more quickly though - especially if you are using lots of heavy DC gear on board whilst charging.
 
You need to look at your needs / requirements. Having spent more than I needed to in the past, I pass on the following points which will probably confuse you more, but could save you money.

You said that you want to replace your old trickle charger so I'm going on that basis.

If all you need to do is to top up your batteries overnight, then one of Stirling's "el-cheapo" Pro-Budget range will do the job (12V @ 20Amps = £99). It's multi stage, small, inexpensive, and quiet. Excellent value for money.

If you believe that you get what you pay for unconditionally on the basis that less dosh means poor quality, then by all means buy the 50 amp charger.

However, if you want to be sensible then my first suggestion will give good results. Quite frankly if you're drawing more than 20 amps continuously (i.e the max output of my choice) then you should have more battery capacity anyway.

I take the view that it's better to charge your batteries slowly as it may (will) make them last longer, so if there's no need to recover the used capacity quickly, then have a smaller (cheaper) charger. Don't forget that if you leave it on while you are using drawing power from the batteries, then you only need to replace the difference (charger power - actual use) overnight.

The Pro Digital range are fine, if you have multiple battery banks to charge then the smaller range can't do that (buy two??), and if you want a quick recovery then again the larger range is better. They are more expensive because they are more complex in their design and use more expensive components. I don't think you need all that.


I have one of each and they both do the job for which I purchased them and I'm well pleased.
 
The max rate of charge is 1/3 of battery capacity so up to 70A should be OK. But - why would you want to bring the batteries up to full charge in only an hour or two when you are likely to be connected to shore power overnight at the very least. On that basis 30A should be plenty.

I too haven't heard of duff kit from Mr Sterling, it's just that he couldn't give Anne Robinson lessons on charm.

To work out the AC load drawn by these chargers, the man himself told me to work on around 65% efficiency. Also, you need to calculate the wattage at the charging voltage (14.8v), not at the nominal 12v. Put those together and you're talking 700w or around 3A at 240v.

Another factor to be taken into account on sizing is the possibility of driving the charger from a generator. I have a cheap suitcase style generator rated at 850w (700w continuous) which should just about be capable of driving the 30A charger but wouldn't look at the demand of a 40A version.
 
I thought of doing the calculations at 14.5 or 14.8 volts, buit I also thought it might confuse the issue - so I allowed what I thought was a generous amount for efficiency. Some switch mode power supplies that I used to work with had efficiencies of up to 90% so I am suprised that Mt Sterling quotes 65% for his chargers. Anyway, it doesn't alter the price of fish as its only another 0.5 amp on what will probably be a 16A supply.
 
20% of the total capacity is usually recommended - ie for 300Ah it would be 60A. But this isn't always practicable. 10% minimum works fine when using a three-stage charger, it just takes a little longer.
 
Thanks everyone for the detailed replies - I shall sit down after work and sift through them in more detail.

Penny
 
Well I'd better let HWMBO come up with the idea or I'll be accused of being a right cheap skate with his birthday present /forums/images/graemlins/tongue.gif - but the idea looks interesting. Does the splitter prevent one battery being dragged down to the charge level of the other (which I always believed was a potential problem) ?
 
Sterlings attitude if something goes wrong is appalling. Very tricky people if you have a warranty claim. I would never deal with them again. Try Adverc or Newmar anyone but Sterling.
 
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