Charging Problem

Goldie

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Advice please folk! My domestic battery bank does not appear to be charging effectively, whilst the engine battery does. The engine battery is approx 10 years old, the domestics (2 x 110 AH) approx 18 months. The problem manifested itself in low charge in the domestic bank despite several hours of motoring in a flat calm the previous day. The french electrician spoke no english and my french is very much of the long forgotten schoolboy level. After 3 hours of deliberations, including taking away what I believe to be the split charge relay to his workshop for testing (C'est bon apparently) he put it all back together again, pronounced himself mystified, collected his money and departed. However, whatever he did - intentionally or otherwise - seemed to work. The visual tell tale was the fridge. It's an Isotherm unit that senses when extra power (higher voltage?) is available and automatically switches to "freeze mode" to store "cold" for future use. The tell tale is that a red light comes on. After our French friend left, the red light came on when we ran the engine - it hadn't just before we experienced our low batteries. We now seem to be back to the same state again in that the domestic bank is low and the engine battery fully charged (voltages without engine running and after a rest period were 12.06v and 12.92v respectively). However, with the engine running, those voltages increased to 12.96v and 13.95v respectively. That to me indicates that some charge must be getting to the domestic bank. Does it?

The charging set up is a 70A alternator through a little green Lucas box (marked with the numbers 33 RA 12v NT and 3345 1B 1288 which I believe is the split charge relay) to 2 battery banks with independent isolator switches (no change over switch). An Adverc charge controller is also incorporated, sensing of the domestic bank and the indicator light suggests normal operation. In the hope of illuminating replies, please bear in mind that the "little green box" description is indicative of my abilities as an electrician - please phrase replies accordingly! Your wisdom is much appreciated.

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Nickcf

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You really need to get hold of an ammeter, connected as near the battery as possible, and see what current is going in/out of the batteries. First check with usual things switched on, but the engine off, what the current flow (out) is. Then run the engine to put the batteries under charge and the ammeter should show current flowing in at several amps depending on charge state. Then check with everything switched off that there is no current flowing out of the battery. If all this looks ok then the battery is faulty.

nb ensure you NEVER run the engine with the batteries disconnected- blows up the alternator usually!

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johna

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It may well be the contacts in the relay that are either burned or not making a good contact. Is the set up long standing or has anything been changed recently? or is this the first time the domestic bank has been low from heavy use? From information I have the Lucas 33RA is rated at 60 amps at 12v so with your 70 amp alternator and the Adverc you may be overloading the relay when the domestic bank is low. I believe most people using an Adverc would install a split charging diode unit rather than a relay, rated at 100 amp+ for yopur setup. The diode does the same job as the relay but there are no moving parts. The diode should have an input terminal from the alternator and at least two output terminals, one for each battery bank.

I am interested in the arrangement you have for your fridge as I want to incorporate a system that will switch the fridge on when the engine is running and give me the option to switch it on when the engine is not running. Will anyone reading this post with such a system let me have details. Should I use a relay (as for split charging) with overriding swich or is there a better electronic system.

John

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Nickcf

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John

To solve your fridge switching requirement all you need is to put a large diode (same sort as would be used in a charging splitter ie about 30A forward current capacity) from the alternator output to the fridge and a second diode in a circuit direct from the battery, via a switch, to the fridge. The two positive ends of the diodes are hence connected together at the fridge end. This is a diode 'OR' circuit where either connection being made will power the fridge but will also prevent either current source from going back up the other direction. Make sure you install fuses though, as near the current source as possible, if not already installed.

Don't forget that the diode will 'lose' about 0.7v across it so the fridge voltage will be around 11.3v when running direct from the battery but this shouldn't be a problem for the fridge. This will be much more reliable than using relay switching.

nick



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charles_reed

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Throw away

the Lucas serial charger and get a simple diode splitter from Adverc.

Personally I find the engine only battery a nonsense and use all 4 of my batteries reserving one in rotation as the panic back-up.

At least with the diode splitter you can check if your domestic bank has a faulty cell somewhere.


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charles_reed

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Throw away

the Lucas serial charger and get a simple diode splitter from Adverc.

Personally I find the engine only battery a nonsense and use all 4 of my batteries reserving one in rotation as the panic back-up.

At least with the diode splitter you can check if your domestic bank has a faulty cell somewhere.


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Goldie

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Thanks John, I'm beginning to think that the relay might be the problem and your technical information goes some way to corroborate that. The system is longstanding - the relay is probably original; which would make it circa 1990. The Adverc was added in about 1996.

As to the fridge; it's a standard Isotherm model. We switch the unit on in economy mode and the cold plate cools to (about) -4 degrees before switching itself to a standby mode, reactivating the compressor by thermocouple when necessary. Without any manual input, starting the engine and (presumably) raising the voltage, the unit switches to freeze mode; only shutting back to standby when either the engine is shut down, or a cold plate temperature of -11 is reached. Should we want to select freeze mode manually, then that is possible too - but we tend to leave the system to its own devices. Works a treat, we switch the fridge on when we go aboard and off when we leave after the weekend/week/month. When everything is working, we never have a problem with power consumption. Thanks again for your help - would fitting a diode in place of the relay be a one for one swop? The relay has one input from the alternator with an output to each battery bank. finally, any suggestions as to suppliers likely to be familiar with the problem?

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Gunfleet

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<<nb ensure you NEVER run the engine with the batteries disconnected- blows up the alternator usually! >>
Good advice but it depends on the set up. Hitachis usually have avalanche diodes, Lucas not. YMMV

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johna

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Goldie
You say <<The relay has one input from the alternator with an output to each battery bank.>>

This makes me think you already have a split charging diode as split charging relays are only required in the feed to the domestic bank, or are you saying the output from the relay feeds each of your domestic batteries and the engine battery is connected directly to the alternator.

If you do already have a diode then may be it has failed. Can you emali me a picture of the green box. I will put my address in a PM.

John

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johna

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Nickcf

Not sure your system would give me exactly what I want. Although I advised Goldie to use diodes and not a relay for split charging, in fact at present I use a relay. So if I connected the fridge diode to the alternator the fridge would run off the engine battery even if the direct battery feed was off. I could of course put a switch in the alternator-diode circuit but that defeats the objective as I can manually select when the fridge runs now.

It appears that there is some circuitry in Goldie's fridge that senses the different voltage and takes advantage of it. Perhaps the relay paralleled with the split charging relay together with an over ride switch is the way to go.

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Nickcf

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john

depends on your alternator setup. On mine there is separate diode pair on the back of the alternator which splits the charge between the engine and accessory battery banks. If you can get access to the alternator output before the diode splitters (fairly easy on my alternators as the terminal is there) and use this feed via another diode to the fridge then it should work ok as this isolates the battery from back feeding the fridge.

Had a look at the isotherm fridge- not come across them before. I guess they have a voltage controlled switch which detects typical charging voltage (say greater than 12.7v) and then switches in the main cooling cycle. The fridge relies on a heavy 'cold storage' plate (which is only chilled when the battery is under charge) to keep the fridge cool in the standby cycle.

nick

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Rick

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Nick wrote:
"all you need is to put a large diode (same sort as would be used in a charging splitter ie about 30A forward current capacity) from the alternator output to the fridge and a second diode in a circuit direct from the battery, via a switch, to the fridge."

ummm - the alternator output (usually deemed to the the B+ terminal) typically remains tied to battery while batteries are on, regardless of engine running condition .......... perhaps a relay on this line driven by the field terminal to feed the engine running diode?

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Nickcf

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yes you're right. I should have added that on some systems with both engine and accesory batteries the alternator has a diode splitter to feed both battery banks. It is usually possible to get to the alternator terminal before the splitter and pick up the supply from there. This would stop the battery backfeeding the fridge due to the diode splitter.

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Budgie

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With the engine running one would expect a voltage of at least 14v. 13v will not charge the service batteries. The Adverc works on a step system with Volts varying from 14.1 to 14.6 if my memory is correct. The first step occurs after 5 minutes. Check your Adverc literature, and then run the engine for a few minutes with a voltmeter across the service batteries and watch for step changes.

Your setup seems similar to that on my Moody. When the engine is running both battery voltages should be the same. Check this with a voltmeter across the batteries, rather than using the boat voltmeters.

I presume you have checked that all connections are sound (not always obvious - give the wires a good tug).

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Goldie

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Re: Diagnosis/solution

Thanks very much to all who posted advice and opinions. It transpires that the "little green box" was a simple split charge relay which was intermittently sticking in the open position. When this happened, only the engine battery was getting any benefit from the alternator. Having considered a number of options - most of which have been covered in the threads below - the relay has been replaced with a Driftgate X-split which came highly recommended from a number of sources. An initial assessment over the weekend indicates all is well and both banks are once again receiving a healthy charge.

Many thanks again to all who responded, I just thought you (someone, somewhere, possibly?) might like to know the outcome.

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