using 12 volt setting on fridge

[Accipiter Nisus]

I've just started my Accordo 105 up for its first trip of the year. I note that with the engine running the voltage at the vehicle battery terminals is 14.24 volts and much the same at the habitation battery - 14.22 volts.This is much as I expected as both batteries are in good condition and are fully charged, so very little current would be supplied to the leisure battery.

 

However, when I turn the fridge onto 12 volts, the voltage across the engine battery remains close to 14.2, but the voltage measured at the habitation battery drops to 13.68 - more than half a volt. (I believe the fridge takes about 10 amps, I haven't measured it). Given the two batteries are only about three feet apart, I was surprised to record such a big difference. I assume there is only one relay pulled in by the alternator which supplies both the battery charging and the fridge via its control switch.

 

I would be interested in any thoughts as to why there is such a big voltage drop, bearing in mind this a fairly new van.

[Alanb]

You do not state what make of 12V control panel is installed in your vehicle. Eldis also are reticent on this matter. It is therefore only possible to reply in general terms.

 

You are correct in assuming 10A or more for the fridge 12V supply. However as regards one relay linking the two 12V systems when the engine is running you are incorrect, unless there is one relay with three connections which are coupled together when the relay is operated. Possible but not common. If you had only one relay it would discharge the habitation battery rather quickly, if the fridge was left selected to 12V.

 

A single power connection to the vehicle battery routed to two separate fridge and charge/coupling relays is more likely. These relays may be incorporated into the 12V control panel.

 

The 12V connection to the vehicle battery should be fused close to the vehicle battery, and this is where I suggest that you start looking for loose or corroded connections including on the fuse.

 

You may wish to note yours is not an unusual problem, and similar problems have appeared on this site in the past. One contributor had problems with poor soldering on a CBE isolation relay "Boite de Securitie" which caused similar symptoms to yours.

 

Alan

[Brian Kirby]

My guess would be undersized wiring between fridge and 12V fuse board, or possibly a poor connection somewhere along the 12V fridge circuit (or both :-)), creating a higher than desirable resistance, and consequent voltage drop.

[Derek Uzzell]

Alanb - 2017-03-16 1:35 PM

 

You do not state what make of 12V control panel is installed in your vehicle. Eldis also are reticent on this matter. It is therefore only possible to reply in general terms...

 

Alan

 

I don’t think it’s going to help, but the drawing of the 12V control-panel in the Accordo handbook is of a BCA GROUP-made unit.

[StuartO]

I agree that without knowledge of the specific Elddis arrangements it's a bit of a guessing game but is it not possible that the voltages being measured are entirely normal for this system, with the engine started but merely ticking over?

 

If the habitation battery is where the 12v power for the fridge comes from (ie this circuit is isolated from the starter batter so it cannot be flattened inadvertently) then you would expect a voltage drop when 10 amps or so is being drawn at tickover revs, wouldn't you?  Does this voltage rise if the engine revs increase to 1500 or so?

 

[Alanb]

The fridge supply must effectively be from the vehicle alternator.

 

If the path from the alternator has a higher than normal resistance, the fridge may discharge the habitation battery when the engine is running, and you are expecting to be charging the habitation battery.

 

This is because the D+ connection or equivalent, will still operate the fridge and battery coupling relays. If the current drawn by the fridge drops the voltage to or below that of the habitation battery, some of the fridge power will flow from the habitation battery.

 

Alan

[Accipiter Nisus]

Thanks for your thoughts. With regard to the control panel, it is a BCA power distribution unit. It's the basic 20 amp model which supplies a permanent regulated 13.8 volts to both leisure battery and 12 volt habitation equipment.

 

I'm taking measurements across the terminals of each battery with the engine running, and the readings are roughly the same at about 14.2 volts until I switch on the fridge, when the reading at the leisure battery drops to about 13.7 volts (remaining at 14.2 at the engine battery terminals). I'm thinking that any high resistance in the fridge circuit wouldn't register at this point would it?. Also since the voltage is well above its resting voltage, which I measured at 12.85 volts, the leisure battery is receiving a charge.

 

I wondered, then, if what I am seeing is the controller regulate the voltage to 13.7 volts when the fridge is turned on so as to avoid damage by over voltage. If that is the case, this controller being fairly basic might well apply the same regulated voltage to the leisure battery under these conditions.

 

Alanb is certainly right about Elddis being reticent to supply any information. I had a conversation with them some while ago on another subject, and they openly admitted that they deliberately provided little technical information in order to stop owners interfering as they saw it.

 

As I stated earlier, the controller is a BCA basic 20 amp model, and I would be grateful if anyone out there knows how these work with regard to the above. Many thanks.

[Keithl]

Hi,

 

The 'usual' or some may say 'proper' way to wire leisure battery charging and 12 V feed to fridge is to have totally separate relays and fuses adjacent to the starter battery and then run separate wires to the relevant loads.

 

But, some manufacturers cut corners and take one feed from the starter battery via a single fuse and relay to the leisure battery and then from there add another relay and carry on to the fridge. This means that the wire from starter battery to leisure battery carries the load for the fridge as well.

 

So if you have any connection with a high resistance, or the manufacturer used low grade wire, then with the load of leisure battery charging plus fridge running you will get a voltage drop much as you are experiencing.

 

To trouble shoot your voltage drop you will have to measure the voltage at every fuse, relay and connection you can access along the wires route to ascertain where your problem lies. It might just be that the length of wire is the cause in which you will have to either upgrade the wire or re-route the fridge wiring as I have previously described.

 

I hope this all makes sense.

 

Keith.

[Alanb]

Hi,

 

A masterful summation by Keith, but may I add that the CBE PC200 system and possibly others use the second method of connection, in that only one connection is made to the vehicle battery.

 

The CBE system also does not use a D+ connection to control power to the fridge, and habitation battery charging. Instead of using D+, a connection is made to an ignition switch controlled supply. The voltage on this supply is then electonically monitored to create a "simulated D+".

 

Alan

[Accipiter Nisus]

Thanks Keith, that makes perfect sense. Indeed, the fact that I drop half a volt at the leisure battery terminals suggests that the fridge could well be connected via a relay in the control box and a single wire from the vehicle to the control box is being used for both. fridge and charging.

 

I assume you don't think the theory in my last post of the charger regulating the voltage to avoid over voltage to the fridge is likely.

 

[Keithl]

Accipiter Nisus - 2017-03-18 3:47 PM

 

I assume you don't think the theory in my last post of the charger regulating the voltage to avoid over voltage to the fridge is likely.

 

I doubt it. (But stand to be corrected if anyone knows otherwise).

 

Keith.

[aandncaravan]

We agree with Keith.

 

The voltage drop you are seeing at the habitation battery, which as noted by Keith is sometimes where the 'real' Fridge supply comes from, is voltage drop from the Alternator to the Habitation battery.

Hence you seeing the drop at that point.

 

The wiring on the Elddis MH's isn't the most chunky going so some voltage drop is likely, but your issue is more probably from the Alternator connection to the Habitation battery being the problem, not from the Habitation battery to the Fridge.

 

Most likely Earth issues, see other Posts.

 

I have a BCA diagram which will most likely apply to your Motorhome if you email me.

[Accipiter Nisus]

Thanks aandncaravan. I did try running a jump lead from the negative terminal of the leisure battery to chassis ground with engine running and fridge switched on, and this only improved the voltage drop by 5 or 6 millivolts, so I suppose it's the positive connection that is high resistance.

 

I would indeed like to have a BCA wiring diagram and am grateful to you for your offer. I will send you an email - I'm new here,so I need to find out how to email through this forum. Thanks again.

[aandncaravan]

Your test with the Jump lead is only testing the battery to chassis connection which is usually sound and assumes the Alternator to the chassis connection is good, when it probably isn't.

 

Try running the jump lead from the Alternator body to the battery negative terminal, that is the one that has the greatest impact on voltage?

[Accipiter Nisus]

Thanks. I'll try connecting a jump lead from the alternator, though having had a quick look under the bonnet, it's not the easiest of things to get at on a 2016 Peugeot Boxer.

 

I originally measured the leisure battery with the fridge on in order to see a small voltage drop by way of proving the fridge was working on 12 volts. What I questioned was whether the amount dropped when measured at the leisure battery terminals (56 millivolts or about 4%) was, let's say, normal for an Elddis Accordo 105 or is due to a genuine fault. I would be very interested to know what other similar motorhomes read under these conditions. I don't really want to tear the van apart in order to redesign it.

[aandncaravan]

"What I questioned was whether the amount dropped when measured at the leisure battery terminals (56 millivolts or about 4%) was, let's say, normal for an Elddis Accordo 105 or is due to a genuine fault. I would be very interested to know what other similar motorhomes read under these conditions. I don't really want to tear the van apart in order to redesign. "

 

 

It depends on what you consider a fault. If the definition includes poor cable design and execution then the answer is yes, but it doesn't need to be.

 

We worked on a brand new Dethleffs in 2016 that had Starter Motor sized cable for all main cabling between the Starter battery and the habitation battery. The architecture was designed to handle high currents passing around the van with real integration and great thought.

One of the design features was to be able to use the batteries at the very rear of the vehicle to Start the engine. Not an 'assist' system, but real "disconnect the Starter battery and operate the Starter button" stuff.

 

The Alternator Voltage to the Starter battery at the front of the van was exactly the same as the habitation battery voltage despite them being mounted at the very rear of the van, even with the Fridge running on Alternator, etc.

 

We were so impressed we documented it here : http://www.aandncaravanservices.co.uk/the-future.php.

 

 

The use of decent sized cable can make a dramatic improvement to charging the habitation batteries and running the Fridge. A Fridge getting only 12.9v can be significantly less efficient than one getting 14.4v.

 

Everyone one knows that most battery chargers 'boost charge' at 14.4v, and the trickle/Float voltage is generally 13.8v. If your Alternator 'boost' phase is 'voltage dropped' to just a 13.8v 'trickle', you can see the potential difference (pun intended) that a 'missing' 0.5v will make.

 

 

The BCA installation is probably the worst we have seen due to far to many connectors and skinny cable.

 

So yes what you are seeing is not untypical, but not normally such a big drop. However, a redesign would give you a more efficient Fridge when temperatures get a bit high, faster and more full charging when on Alternator. The BCA mains charger is often only 13.5v so cabling won't make a lot of difference to that.

 

Especially a good idea on UK built vehicles if you want to add a second battery.

 

Many people fit a B2B at great cost, when close on the same effect (or even better because battery drying out voltages are not employed) can be achieved just by putting in decent cable 'battery to battery to Alternator'.

Further installing a 100amp Split charge relay (£7 on ebay) that has really chunky contacts (chunky contacts will give better long term conductivity through reduced resistance from burning/wear) plus screw/clamp terminals instead of the Spade type.

See : http://www.ebay.co.uk/itm/Universal-12V-100Amp-4-Pin-Heavy-Duty-ON-OFF-Switch-Split-Charge-Relay-For-Car-/262101152648?hash=item3d06723388:g:yx4AAOSw5VFWJGnl