narrowboatworld

Hi Martin,

Before spending over a grand on a gen I would consider a solar panel first.

I have a 100 watt panel and it is brilliant at keeping battery levels up and even completely charges to 100% when in marina not being used.

I no longer have the boat connected to landline over the winter and very often when using the boat I find that the percentage (say 80%) reading as we go to bed is the same if not more when we get up in the morning (as long as I set the angle for the sun in the morning) and that is with the fridge on.     Best wishes, steve

Hi All,

           I have just returned home for a short visit and can catch up with the discussion. My electrician has spotted that my fridge was wired up to only one battery. This has now been rectified. In addition my isolator switch has pitted contact faces causing high resistance, which will be replaced shortly, and new Mega fuses fitted. When I have my fourth leisure battery things should be much better.

           I would appreciate your views on whether to buy a small whisper generator rather than run the engine, when moored up for longer periods.

                         Cheers Martin.

Not at all, I know that you know what you are talking about but I also know there are probably more boaters who have wrong ideas about how their batteries and charging systems work that who have the correct idea so I try to minimise any misunderstandings.

TB

Thank you Tony,

You are, of course, correct, the Zener diode is a voltage operated device - as was the Neon stabilizer before it I agree also that the design and correct use of lead acid cells and batteries is a complex subject, especially for the uninitiated. 

However, I was only trying to add a slightly different slant to your answer to the original question. Sadly, having retired from teaching electrics & electronics 15 years ago, I obviously over simplified. Having designed many stabilizer circuits over the years I should have known better.

I hereby apologise if I ruffled your feathers somewhat.

Keep up the good work.

Kind regards,

Derek

nb Kit

I do not want to be picky but zener diodes do not react to current, they react to volatge. On the motor cycles they "opened" at the designed safe charging voltage and conducted to negative. This produced a voltdrop across the diode (or across a diode and heavy current resistor) then prevented the voltage rising. In effect it probably kept opening and closing very fast so the average volatge is that designed into the system.

There is still a zener diode in the alternator regulator and it is still only reacting to volatge but this time when it "opens" it feeds a transistor that in turn "opens" and turns another transistor off. This transistor is the one that feeds current to the spinning rotor inside the alternator so with the transistor turned off, no current flow in the rotor and thus no magnetic field the alternator voltage falls (it would go to zero give time). However as soon as the output voltage goes below the pre-set voltage the zener diode turns off and the transistor turns on allowing current back into the rotor. So with the alternator the magnetic field is turned on and off many times a second but the zener diode is far smaller than the motor cycle one and carries a very small current - hence no, or very small,  heat sinks on may alternator regulators - unlike the motor cycle one.

The current flow is "controlled" by the voltage difference as described BUT the maximum charging current is designed into the alternator so it can never exceed its designed maximum charging current. This is achieved by a sort of "back volatge" caused by the strength of the AC induced magnetic fields in the alternator working against the charging voltage. The maximum voltage an alternator can achieve at full output first thing in the morning could be as low as 13 volts, but it is usually a bit higher than this but the current will be at maximum.  As the charging current falls the charging voltage gradually rises until it reaches the regulated voltage of typically between 14 and 14.5 volts or so (more on some very modern alternators) and at that point the regulator starts to work.  No "advanced" controller can do anything up to the point the regulator starts to work because the alternator is already delivering maximum current.

I would also point out that an advanced regulator can not burn an alternator out. However insufficient cooling will and it often only shows when an advanced regulator is fitted. so the regulator get the blame. (there have been a very few crap alternator designs that did fail but it is very rare). I also get fed up with people saying that high charging voltages on first start up will blow bulbs etc.  This is just plane wrong because the volatge is depressed, not raised.

Once the regulated voltage gets to 14.4 volts and above the effectiveness of any advanced regulator (or alternator controller - same thing) must be open to question. If they appear to work they are probably covering up a fault in the charging system wiring/splitting. To be sure you have to know the gassing volatge of the batteries because once they start gassing the extra current you see being delivered by the advanced regulator has a significant amount wasted in breaking the water down into hydrogen and oxygen.

Tony Brooks

May I add a bit more to TB’s explanation about battery charging?

Generally, an alternator can be considered to have a fairly constant voltage output – about 14.6 volts these days I think. The result is that when a working alternator is connected to a discharged battery, the voltage difference from alternator to battery is relatively high and therefore a high charge current is produced. Current is directly proportional to the voltage difference. This high current may be limited to a safe value by a Zener diode and associated circuitry or bysome other means.  

As the battery charges, its voltage increases and the voltage difference between battery and alternator decreases. The charging current consequently falls.

It is worth noting that some battery management systems maintain a high charging current by electronically sensing and adjusting the alternator voltage to maintain a relatively high difference in alternator voltage to battery voltage to keep the charging current high.

That was a Zener diode that simply "dumped" excess currant to earth. It needed the heat sink because it got so hot.

Some solar regulators may do it in a similar way but alternators definitely do not.

The voltage regulator alters the effective strength of a spinning magnetic field so the alternator only produces the voltage per-set in the regulator. (see TB-Training.co.uk in the electrical notes)

Tony Brooks

Isn't any 'spare electricity' lost as heat through a heat-sink on the alternator regulator pack. I haven't looked at mine, but I remember back to my days on a motor bike, there was an air cooled heat-sink under the battery.

If that is the case, it's a shame to be heating something up with no other use.

I have a switch on the wiring from the solar panel for off or domestic or starter.

There is also a 10 amp max ammeter  inline so I can see how much I get.

Here's a question and I know it may sound silly but when the batteries are maxed out where does all that energy go?  like when the alternator stops charging but you still motor on for hours, what happens to the energy generated?  Guess this one is for tony brooks.

Interesting, I like the sound of that. I've been tinkering with a small 15w or 20w 0 .81amp solar panel, the results at this time of year surprised me even for such a small panel. Recently I put it on my cranking battery (86amp/h deep cycle) after the battery was charged by a 35amp alternator. It sat there doing it's thing on a patchy cloudy/ sunny day. I checked the volts and nothing seemed extraordinary, about 13v or so. Next day I turned the engine, it's never started so well. I can only assume the steady trickle topped the battery beyond what the alternator could give. I'll be investing in a bigger panel when my finances allow it. That and a smart gauge type of thing.

My batteries are also around 8 years old, I want to add another one, but I'll wait until these expire first.

(Apologies to the OP for deviating off the original post).

Hi,

I have had a smartgauge for seven years now and I swear by it.

it is the best monitor out there and you actually get 100% , albeit declining with age, but I can still go 36 hours before it gets down to 70% where I run the engine or move on of course.

Together with adverc battery management and an 1800 heart interface inverter/charger.

A domestic integrated fridge (AC), microwave, 20" lcd tv, satellite dish and god knows how many gadgets like walkie talkies,  my batteries have so far lasted 8 yrs.........oh! and 18 mths ago got a 100 watt solar panel.   So am happy with my set-up

Hi Martin,

I'm no electrical expert, and my boat and TV  are all 12v. My fridge is gas though.

The trouble you're having there I reckon is the shut down thresh hold of the fridge and the inverter, the fridge may have a higher voltage setting, so it trips off and the inverter enjoys the extra available voltage.

I spend a lot of time looking at and monitoring my battery input/output and usage just so I know what's going on. My 12v TV draws 5 amps and I can watch it for  6 hours or more without fear of dropping below 11v. It may drop further, but the voltage bounces back overnight. I've got 2x 110amp/hr batteries in the bank and they are a bit old, but so far they do alright. I wouldn't like to put them up against a fridge and an inverter though, not both running at the same time.

As for a generator set, If I had the space and the money, I would use one. Small, portable, quiet and will run a decent mains charger to get keep the batteries topped up properly without the engine wear or alternator  imperfections.

Sorry I can't answer your question on the draw of your TV volts watts, amps.. How many watts at 240v is it ?

Thanks everyone,

                              I appreciate the answers so far, but I wonder about the way for me to proceed. Does a 240v tv use more power than a 12v of the same size ? Also is a silent petrol generator the better way than a bigger alternator, mine is a 70a ? The engine has done nearly 7000 hrs, and I understand I should stop running it under no load.

                        Martin.

A SmartGauge is another device for monitoring battery condition. It does this in a relatively unique manner by accurately measuring battery volts & the small changes in such which determine battery state. Programmed with battery capacity & type it builds up a profile of their performance & can thus allow for aging & other vagaries.

It can't measure drain or charge current, but the amp/hr (SOC) counter doesn't go out of sync as any shunt based battery monitor inevitably will. Not requiring a shunt its probably easier to fit as well.

Hi Martin,

To add to Moonie's excellent reply; I've fitted a Victron BVM600 battery monitor to my boat. This has a current shunt supplied with it, so it not only monitors battery volts, but if installed correctly, monitors all the current going into and out of your domestic battery bank.

Better still because it integrates that current with respect to time it gives a reading of Ampere Hours (plus and minus).  With this device you can not only monitor how many Ah you have used since your last charging session, but by switching loads on and off you can see exactly where the current is going.

As Moonie alludes to at the end, I'm one of those that doesn't move every day, so energy monitoring, especially with the current price of diesel, is very important.

Ralph

Hi Martin

Don't rush out spending money without checking out a few things first.

The fridge will be stopping because it has sensed the battery voltage is too low. (probably 11.0 to 11.5volts). What diameter cable runs to the fridge? It should be pretty thick, someting like 10mm2 for best effect to minimise voltdrop.

I guess the invertor is connected quite close to the battery bank with 25mm2 or fatter cables and the invertor will probably work down to a battery voltage of 10.5 or 11.0 volts.

It is worth getting a multimeter and checking actual voltages around the electrical system with everything running. Check the battery voltage on the battery, the fridge side of the fuse or circuit breaker (there should only be a very small difference in voltage here with the fridge compressor running) and the down to the fridge where if the cables are nice and thick maybe a 0.2-0.3v less than the battery.

On a slightly different note a 70Amp alternator is going to struggle to maintain a decent charge in your battery bank without running for 3 or 4 hours. OK if your are cruising most days but a pain if you are moored up for any period of time.

Steve

I have recently puchased a second hand 62 foot narrowboat. It has a 12v fridge, 1800w inverter, 3 soon to be 4 x 110v leisure batteries. Charging is done by a 70A alternator using a pdar digital charger.

My problem is that when I watch my  240v led tv the fridge stops working after 3 hours. Although the inverter will continue to work the tv for much longer.

I need to know how to proceed. Do I use a 12v tv ? Do I convert the fridge to 240v ? I want to avoid a gas fridge if possible. Do I buy a small generator ?

Would appreciate any useful advice or people to talk to.

                                            Thanks Martin