508 - battery block

[Deadsfo]

I apologise for posting in English but I do not speak any Dutch,I post here because it has more information on Merc 508's than anywhere else I have an Ex Nato ambulance1987 ,there are many of these ex nato ambulances on this site ,I hope to ask many questions
if you answer in Dutch I can translate on google. My question is ,what is the electric block with the cables from the battery attached that sits on the drvers side step, and what does it do,I have attached a picture.
Thank You

[Admin]

Hi Denis,

The box you show looks like a "series/parallel relay". In normal driving conditions and when standing still, the two batteries are switched in parallel, thus giving 12 V and a capacity of twice that of a single battery.
For long life the two batteries should be identical.
The moment you touch the start button, one battery is switched off from ground and its minus pole is connected to the plus pole of the other one (switched in series). So there is 24 V available for the starter motor. When you release the button the two batteries return to the parallel situation. The alternator and all other electric parts are 12 V.
If you have the instruction booklet, there is an electric diagram somewhere in the back.

I thought NATO ambulances all worked completely on 24 V, but apparently there are different versions. The 12/24 V version is common to most civilian 508s.

CORRECTION
When I looked closer to your picture, I missed some fuses and some wires.
Your relay is a main switch for heavy currents. There should be a switch somewhere on the dash, which operates this relay. You should be able to hear a click when it comes in.
Sorry for the confusion.

[Anton]

Hoi,

Ernst heb je dat wel goed?
Er staan twee dikke kabels op, het lijkt mij eerder een zeer zwaar relais / hoofdschakelaar.
Helaas is mijn Engels niet so good...

Groet Anton

[Admin]

Anton,

Je hebt het goed gezien: het is een zeer zwaar relais! Ik dacht eerst het serie/parallel-relais om op 24 V te kunnen starten, maar dit exemplaar heeft een paar draden minder.
Het is de hoofdschakelaar voor de hele elektrische installatie. NATO, dus degelijk.

[Deadsfo]

Hi Denis,

The box you show looks like a "series/parallel relay". In normal driving conditions and when standing still, the two batteries are switched in parallel, thus giving 12 V and a capacity of twice that of a single battery.
For long life the two batteries should be identical.
The moment you touch the start button, one battery is switched off from ground and its minus pole is connected to the plus pole of the other one (switched in series). So there is 24 V available for the starter motor. When you release the button the two batteries return to the parallel situation. The alternator and all other electric parts are 12 V.
If you have the instruction booklet, there is an electric diagram somewhere in the back.

I thought NATO ambulances all worked completely on 24 V, but apparently there are different versions. The 12/24 V version is common to most civilian 508s.

CORRECTION
When I looked closer to your picture, I missed some fuses and some wires.
Your relay is a main switch for heavy currents. There should be a switch somewhere on the dash, which operates this relay. You should be able to hear a click when it comes in.
Sorry for the confusion.

when starting the van I have a funny looking key that looks like a carpenters nail,this is pushed in and turned ,I then push in a button on the dash that switches on the battery,I guess this activates the switch I am asking about,I then push the starter button to start the van .
I was told of the 12/24 volt thing but everything i have tested has been 24 volts so your suggestion that it is simply a big switch
is probably correct
There are not many 508,s left in England ,and not many mechanics left who no anything about them

[Leo]

Is een hoofdrelais, waarschijnlijk op massa.
Hetzelfde relais zit op m'n O303, wordt ook met een aparte schakelaar bekrachtigd nadat de contactsleutel is ingedrukt.

[GerardM]

This is indeed the main relay connecting the battery ground to the chassis of the truck. It is activated by a switch on the dashboard, the switch has an indicator light in it. This relay is also found in the Dutch version of the ambulances.

Regards,

Gerard

[Admin]

So the experts agree: it's the master relay.

The funny looking key (in Dutch called "spijker"="nail") operates the contact switch by just pushing it in. Turning it switches on the lights, one click: parking light; two clicks: main beam.

[GerardM]

Turning it switches on the lights, one click: parking light; two clicks: main beam.

That is indeed the standard behaviour, however in the NATO vehicles this function has been moved to a separate light switch to the left of the dashboard, including black-out lighting.

Regards,

Gerard

[Admin]

Thanks for the addition!

[Arno Z]

My 608 is currently in pieces because of restoration, so the starter/main relay are not build in. Easy to take a picture of.

The main relay is of a different make and type than yours, but should have the same functionality. The starter relay is probably mounted in the battery compartment under the driver's seat.

Welcome here, by the way. I hope Google Translate can make something useful out of all the mumbo-jumbo here.

[Deadsfo]

My 608 is currently in pieces because of restoration, so the starter/main relay are not build in. Easy to take a picture of.

The main relay is of a different make and type than yours, but should have the same functionality. The starter relay is probably mounted in the battery compartment under the driver's seat.

Welcome here, by the way. I hope Google Translate can make something useful out of all the mumbo-jumbo here.

Thank you for the kind welcome ,Google translation can be a bit hit and miss but I read 'between the lines' and get an understanding
I think my 508 is a little different to yours.I only have the switch (shown in my pic.) there is not another switch in the battery box under the seat ,unless I heve not found it yet.
Thanks for the answers to my question ,the answers to many questions I would ask are already on this very informative site.

[Deadsfo]

Turning it switches on the lights, one click: parking light; two clicks: main beam.

That is indeed the standard behaviour, however in the NATO vehicles this function has been moved to a separate light switch to the left of the dashboard, including black-out lighting.

Regards,

Gerard

That is exactly how mine is set up. not surprising really as we seem to have the same vehicle

[Wolvesamongus]

Hi and sorry to kinda hijack this thread started by fellow Englishman Deadsfo but the problem I have is built around the same components i think having the same Bus, when I insert the key I get a double loud click from the relay on the drivers step when there was no click before as well as a single softer click when pushing the battery button to the left of the steering wheel this I understand is normal? the loud clicking from inserting the key or as Deadsfo Says nail has only just started strange thing any ideas please?
Regards----Kim

[GerardM]

The double-clicking of the relay could indicate a short voltage drop. Have you checked battery voltage ? Any new/additional installations done that could cause this ? Does the bus start at all after this ?

Regards,

Gerard

[Wolvesamongus]

Hi Gerard, thanks for the reply the voltage is good and the bus fires into life first time always, I have fitted a Durite voltage sensitive relay between the start and leisure batteries with a cut out switch just the other side of the start battery so that should not be a problem as I only turn on when the bus is running. When the key is inserted there should be no click only a single click when the battery switch is pushed in, I will check the voltage again in the morning it will be Ok always is.

Regards--------Kim

[Wolvesamongus]

Update, I left the bus standing for 48 hours and checked voltage early on a cold morning 25.6v was the result so OK, if I push the battery button in first there is one click on the relay normal, then put the key in there is no click dash lights come on normal, if I don't push the battery button in and then insert the key there is a double loud click on relay dash lights on is this a problem? It's just that when I first had the bus and put the key in there was no click on the relay only when the battery button was pushed in did I get one click on the relay, I am thinking auto electrician now, he will have much fun my wiring diagram and codes are in Dutch
Regards-------Kim

[melvin]

Normally this relais in the doorway is for the mass of the starter batteries, but if you make an extra mass (the mass of youre lighting batteries) he doenst do his thing anymore what he should to do, the electricity goes now over the - of youre lighting batteries.

Maybe youre relais stays connected, in that case the switch on the dashboard had no sence because you get youre earth from youre lighting batteries. You can remove the earth of youre lighting batteries and try it again..

Sorry for my bad English but i think you wil know what i mean