Bro

Hi Tony. I may well have a poorly specified charging circuit, I don't know. Having two alternators, one for engine start battery and other for aux/ domestic battery bank It looks conventional to me. Boat instruments indicate both alternators charge at your 14.4 to 14.6V. I do know that after a short time, though the voltage remains high the amps output falls away dramatically and consequently it takes longer to charge the batteries. I had assumed alternators with battery sensing might maintain high output for longer.

Recent interweb trawl for an alternator seemed to indicate Battery sensing jobbies are becoming more readily available at sensible prices. As an alternative to additional systems for faster battery charging (such as Adverc, good as they are) do they now make sense on our narrow boats?

Thank you gentlemen. Seems there is nothing for me to worry about and I don't even have to insulate the terminal.

Apologies Tony for tardy response but have been away some time. Photo attached which shows the alternator terminal marked 'B-' which seems not connected to anything. It's positioned just below and to the left of the 'D+' terminal (black/ yellow cable to warning lamp). Ought this 'B-' terminal be connected to anything? And if not then ought it be insulated? Alternator is not giving problems, I'm just curious.

Subject alternator has B- terminal (having small spade type tag) which is the only terminal not connected to the loom. I should say there is a heavy cable from the alternator which goes to earth/ battery negative. The alternator charges batteries fine. Question is, ought the spade connector B- be also connected permanently to the battery neg or earth (same thing effectively) or to somewhere else or not at all?

Many thanks. I'll do just that as soon as I get back to the boat (week or so).

Would "Oil Pressure sender" or "Temp sender" circuits cause the alternator warning light to activate? I'm no electrician.

We don't. Simply that both alternators seem OK yet the warning buzzer and engine alternator warning indicator light are active so I'm looking for possible cause. Buzzer diodes seem worth a check. Shall be grateful if you have other suggestions.

Thanks Steve.

Thanks Steve for clarifying resisters issue (yes they are wired across the two warning lamps as you say). Not at the boat at present but took a photo of panel wiring before leaving last time and yes there does seem some plastic tubing on various cables so I suppose I must cut the tubing away to find diodes. Having only a little electrical knowledge I assumed the diodes would be of reasonable size and clearly visible. Can you suggest diode spec. I might ask for at Maplins?

I'm not an electrician so need help. Isuzu 35 engine with standard wiring and engine control panel. Problem:- Control panel warning buzzer is sounding, not continuous but with frequency increasing with engine revs, and engine alternator warning light is similarly showing. On board electrical panel indicates engine alternator is pushing +14.4V and charging amperage is satisfactory (as is auxiliary alternator), both engine and auxiliary batteries charge fully no problem. Both alternators bench checked OK so, looking at the Isuzu wiring diagrams I see 3 diodes at warning buzzer and thought I'd check them. NO JOY! Can't find diodes in panel wiring at all but do find 2 resisters (CGS SBCHE4 47R J PW LA) which according to the diagrams ought not be there. Shall be grateful if someone will tell me what's going on as the sound from the warning buzzer is driving me crackers and I don't really want to disconnect it as it serves as warning for oil pressure and water temperature as well as engine and auxiliary electrics.

I don't understand your reply. Which is the best way to connect the alternators to the batteries, via the switch or not?

Not a split charging system! Boat has two alternators, one for domestic batteries t'other for engine battery and each has isolation switch. If the alternators were to be connected direct to the batteries (not via the switches) then with engine not running and switches open, the alternators would still be connected to the batteries. So, would that be a problem in any way? Effectively, could there be issues with batteries permanently connect to alternators?

Is it better to connect the alternator to the battery via the isolation switch or direct to the battery terminal, or does it make no difference?

Some time ago there was thread here explaining how to convert a small table top 230V freezer (much better insulation than fridge) to run as a fridge and use the inverter on demand (only comes on when fridge wants it). I don't need a large fridge so I followed the advice. Bought 2nd hand newish freezer (£30) and I find that if I don't go into it too often it holds temp for just under 1hr and when the inverter does cut in it pulls about 4 amps for about 5 mins. That'll do for me.

Hudl is great (for me) but they did have issue with charging voltage being critical. If you buy the latest Hudl charger you might find it works well enough. Do not be tempted with alternative chargers.

It is quite possible to wire and control an AC freezer to run as a fridge (better insulation) and have the inverter cut-in on demand only (thus limiting inverter loss). Bear in mind that when running the engine (travelling) inverter loss will be insignificant. I would however switch off the inverter when asleep or away from the boat and also ensure a good fire extinguisher is always in the vicinity.

Consider using strong plastic tie-wraps. If the button does get caught up on a lock door it will rise until the wrap tension gets too much and then snaps. Result, your boat doesn't get flooded and sink.

Thanks for the link Smiley. Seems there are no adverse reports on the Sunshine Solar inverters so I reckon I'll go for the 1200W jobbie at £159 which will hopefully deal with the fridge start-up load.

I spoke with Sollatek who say the Freosave is intended for OEM supply to be inbuilt to fridges. They would not be happy to supply over the counter for after fitment. Shame!

Has anyone tried inverters from Sunshine Solar? Their 'Sunshine Power Inverter 1200W 12V Pure Sine Wave' claims "2400W SURGE POWER; 1800W for 10sec, 2400w for 2sec". For £149 a pop it sounds a snip (if it's for real and is reliable).

Thanks for all the good stuff. I'm away from the boat at present so can't give details about inverter and haven't tried using it with engine running. I can say though that batteries are 110Ahr x 2, fully charged and cabling is of substantial thickness. Circuit from batteries (+) to inverter is through isolator, 150A shunt, 120a relay then back to batteries (-). Apart from the 120A relay this circuit is in accordance with instructions for MCS Boat Products "15Amp DC Panel".

Thanks Paul. I used your link to the calculator which, based on freezer annual power usage of 150kW/hr, suggests a 500W start-up and an inverter having 317W min. output should do it. The inverter I have is rated 800W but doesn't work so something is adrift. Any ideas?

And that size would be?

My present inverter is too small to fire up a Curry's table top freezer (model, Essentials CTF34W15) and whilst I'm resigned to buying a larger inverter I'm loath to buy one that's over-big for my needs. Would soft start unit such as "United Automation 25 A Soft Starter, 230 V ac" (RS Stock No. 330-5358) be helpful?