12V problem

[Morag123]

Hello I wonder if anyone can help me please. I have an oldish 54plate lorry that has a PC100 control system in its living area. If I am plugged in to 240V everything works perfectly but I'm having no joy using the 12V battery system. Ive replaced both the batteries that are used to run the system and the control panel. With two fully charged new batteries when I press the main power switch on the control panel I just get a green flashing light indicating low battery charge or voltage. Has anyone got any ideas please?

 

[MichaelT]

There is probably a biggish fuse near the batteries have you checked that?

 

[autorouter]

The PC100 is the control panel of the system, there should be another 12V fusebox and distribution unit somewhere, maybe hidden away in a locker or cupboard. It should have a label showing the model number. Like these, maybe:

CBE PC100 PMS Kit control panel charger consumer 12v 240v campervan motorhome | eBay

CBE PC100 Kit - New sealed box. The CBE Fresh Water Probe is not included as available in various lengths. The PC100 Kit includes PC100 LED Display Panel. DS300 12v Distribution box & fuses. Waste couple screws, connections and pins.

www.ebay.co.uk

One box for the mains 240V switches, one battery charger, and one box for the 12V stuff.

That 12V box will have a thick wire going from a heavy-duty terminal to the leisure battery. There should be a big fuse, maybe 30A to 50A, in that wire very near the leisure battery. That's the first thing to check, if you're sure the leisure battery itself is OK.

Another question, when you say 'both batteries' do you mean a pair of leisure batteries connected together to make one big battery, or are you talking about the leisure battery and starter battery?

 

[Morag123]

Thanks for getting back to me. I was looking for responses but didn't realise I needed to refresh the page! anyway I know now. So Ive checked the fuses and have also checked that I'm getting 12V as the supply to the new distribution box, I replaced the old one as thought this was the problem. And correct it is a DS300.
The lorry has two leisure batteries we are not 100% sure why but assume it is something to do with the fact that it cannot run from the 24V system which powers the lorry, both of them are brand new and fully charged.

 

[autorouter]

The lorry has two leisure batteries we are not 100% sure why but assume it is something to do with the fact that it cannot run from the 24V system which powers the lorry, both of them are brand new and fully charged.

Yes I was going to ask about that. You need to know that 12V batteries can be connected in two different ways: series and parallel. These must not be mixed up.

Positive to positive, negative to negative is called a parallel connection. Two 12V batteries in parallel make one big 12V battery. This is used for example to make the capacity of the leisure battery bank bigger, so the power lasts for more nights off-grid. It is very common in many motorhomes.

The other connection method is called series connection. The positive of one is linked to the negative of the other. Power is taken from the other two positive and negative terminals that are not linked. Two 12V batteries in series makes a 24V battery. The vehicle electrics of the lorry will be 24V.

As I'm sure you know, habitation electrics are nearly always 12V, because things like 12V water pumps, lights, fridges, heaters and water heaters all run from 12V. With the information above, you should be able to look at a pair of 12V batteries, and see if they are connected in series (24V) or parallel (12V).

The lorry engine will have an alternator, which will output 24V, and will charge the lorry starter battery. There may be some arrangement for charging the 12V leisure batteries. This could be a second alternator, with a 12V output, or a 24V-to-12V DC-DC Converter Charger that can charge a 12V battery from a 24V alternator.

This mixture of 24V and 12V electrics is usually only seen in big motorhomes and RVs ('gin palaces') so it's a nice problem to have.

https://www.power-sonic.com/wp-content/uploads/2020/08/How-to-connect-batteries-in-series-and-parallel.pdf

^{_{Subscribers  do not see these advertisements}}

 

[Morag123]

Yeah we've tested the supply and it is very definitely only 12 V at the distribution board so batteries wired in parallel. Again your right the alternator has a 24v to 12v dc converter. I was going to change the Pc 100 control panel thinking maybe that could be the issue having changed the batteries and distribution board but thought id ask for an opinion first. What is so weird is that everything is perfect when plugged in so it is only an issue on 12V. Maybe there is a short that makes the distribution board solenoid not receive the full 12V of power?? Or a dodgy wire somewhere.

 

[autorouter]

The PS300 is usually used for a motorhome or caravan with a 12V starter battery, and a 12V supply from the alternator. There are three big bolt connections at the lower edge of the PS300 PCB, labelled -B2, +B2 and +B1. The leisure battery connections should be connected to -B2 (negative) and +B2 (positive). What, if anything, is connected to the +B1 terminal? Do you get 12V between the -B2 and +B2 terminals?
Another question, has it ever worked properly?

I think there is a problem with the thick power wire from the leisure battery to the PS300 +B2 terminal. There should be a 50A fuse very near the leisure battery, check that is OK. Do you get 12V at the +B2 terminal when the mains is unplugged? I'd go back to basics and put the meter negative probe on the leisure battery negative, and check you get 12V at: the positive battery terminal, the positive terminal clamp, the 50A fuse input, the 50A fuse output and the end of the wire at the +B2 terminal.

 

[Morag123]

Amazing thank you I will try that later and report back. Yes it has worked in the past just FYI.

 

[Morag123]

Thank you so much for your suggestions. Turned out that there were two earths that weren't fantastic and that in the end the main power supply wire from the main leisure battery must have been shorting somewhere when a load was put on it. Anyhow suffice to say now all back up and running thank you.

 

[MisterB]

Pleased that you got everything sorted.

Perhaps the responses and help you got, saved you a lot more money than an annual subscription would and might come in handy further down the line? I have found that there is always someone who has had a similar issue or can offer the correct advice, which for me, more than covers the subscription...

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[HKF]

Yes I was going to ask about that. You need to know that 12V batteries can be connected in two different ways: series and parallel. These must not be mixed up.

Positive to positive, negative to negative is called a parallel connection. Two 12V batteries in parallel make one big 12V battery. This is used for example to make the capacity of the leisure battery bank bigger, so the power lasts for more nights off-grid. It is very common in many motorhomes.

The other connection method is called series connection. The positive of one is linked to the negative of the other. Power is taken from the other two positive and negative terminals that are not linked. Two 12V batteries in series makes a 24V battery. The vehicle electrics of the lorry will be 24V.

As I'm sure you know, habitation electrics are nearly always 12V, because things like 12V water pumps, lights, fridges, heaters and water heaters all run from 12V. With the information above, you should be able to look at a pair of 12V batteries, and see if they are connected in series (24V) or parallel (12V).

The lorry engine will have an alternator, which will output 24V, and will charge the lorry starter battery. There may be some arrangement for charging the 12V leisure batteries. This could be a second alternator, with a 12V output, or a 24V-to-12V DC-DC Converter Charger that can charge a 12V battery from a 24V alternator.

This mixture of 24V and 12V electrics is usually only seen in big motorhomes and RVs ('gin palaces') so it's a nice problem to have.

https://www.power-sonic.com/wp-content/uploads/2020/08/How-to-connect-batteries-in-series-and-parallel.pdf

This subject is of no consequence to me but I like to learn and understand things. Your response to this post is so plain and simple (with every respect!) that even I understood it Every day's a school day