improved charging

[dor]

I recently bought a new radio for the boat, which needed a continuous feed to maintain the memory (30 ma – so only 5 amphrs per week). Now my battery isolation was on the negative, so this meant I would have to run a separate negative wire back to the battery or change the isolator. The former would mean that when the power was off, the radio wouldn’t necessarily be off so ran the risk of sooner or later being left on. This situation draws considerably more than the maintenance current of 30ma, so I wasn’t so keen to do that.

 

I decided it wouldn’t be too big a job to swap over the isolator to the positive (which is the recommended method anyway). Aquafax do a double pole isolator, which I used on the two positive battery cables, and a “powerpost” (basically a bolt set in an insulating base) which I used to replace the original isolator to join the negative cables. I also replaced some of the thick battery cables

 

Why am I telling you this?

 

After completing the job and starting up the engine, my charging rate had increased by over 25%. I have been concerned for a long time as to why my relatively new 110Ahr Elecsols seemed to have so little capacity, even after a days charging. Also very noticeable was the speed the engine turned over after only an hour’s cruising the night before.

 

My conclusion is that the old isolator switch had a slight resistance – probably only an ohm or two- which affected the regulator enough to restrict the charge. As the resistance in the charging circuit is very low, a significant voltage drop could occur across a few ohms resistance in the switch. (This is of course why split diode charging systems often significantly reduce the charging capacity due to a 0.6 V drop).

 

What is odd is that I have an external (Stirling) regulator with a battery-sensing wire. Theory says that this should increase the alternator voltage to compensate. Maybe it is because the resistance was on the negative side.

 

Anyway, the moral of the story is: If you think your batteries don’t have the capacity you think they should, check out the components in the charging system: switches, relays and cables, for even a slight resistance that shouldn’t be there.

[John Orentas]

DOR.

 

The suspect isolator, was it one of those with stud connectors and a nice red ramovable plastic key?

 

I have found problems on three occasions with friends boats in the last year, they seldom fail completely but as you say they show a high restance accoss the contacts. There are three or four sizes of these with stud sizes varing from 8 - 12mm.

 

The larger sizes seem ok but the smaller ones suffer from very weak spring pressure closing the contacts. All the problems have been with cruiser style boats, I think the damp conditions don't help.

 

Drill out the rivets and take a look at the contacts, if I am right you will find evidence of arcing on the brass contacts. Please let me know.

 

'Call me picky', but strictly speaking you should not be bye-passing the isolator for a normal radio. The regs. say only bilge pumps and navigation equipment requiring memory back-up.

 

John Squeers

Edited October 25, 2004 by John Orentas

[dor]

John: The isolator does have a removable red key, but was fairly substantial, with 10mm termimnal posts. I'm keeping it as a spare - just in case (my life is full of stuff that only half works, but "may come in useful sometime" much ro my wife's despair - however I have just fixed up my old boat radio in my garage, using an old transformer I found in the back of my garage and the diodes out of a 20 year old Scaletrix power supply that didn't work).

 

I understand that electronic equipment such as a radio is permitted to have a permanent supply provided it is appropriately fused "as near to the supply take-off as possible".

[John Orentas]

DOR

 

The isolator is only a medium size one, there are I think two larger sizes both with 12mm studs. I still think you should open it up and clean up the contact surfaces, if only out of curiosity, you can re-assemble it with screws and nuts. (you will probably see what I mean about weak spring pressure).

 

I have checked the book, it specifically mentions "bilge pumps, security alarms, fire pumps and navigation eqipment - some of which may have electronic memories". However it does say "such as".

 

John Squeers