Adding 'House' batteries to my MK7 Transit. (Standard Starter & Auxillary Batteries)

[nickdrye]

I have a 2012 Transit (2.4L Diesel Duratorq 115PS). Following some starting problems, I had the battery fitness checked at Halfords, their basic battery tester classified each of the batteries as 'shagged'. I didn't know until now that the batteries were independent of one another and that one is designated as a starter battery and the other is for the vehicle's accessories, learning this caused me to wonder if my installation of additional batteries may have caused a problem.
My additional batteries (3# 120Ahr) are mounted over the back axel and are there to service a couple of inverters and a handful of small 12v DC loads. It turns out that I had connected these three 'House' batteries to the Starter battery so when the Starter battery began to fail it resulted in the starter motor drawing too much current for the 100A fuses on the link cable.
From what I have read recently, it seems that the vehicle batteries are connected/separated using a split charge set-up so I now believe that I should have connected my House batteries to the vehicle's own Accessories battery.
HOWEVER:
I have to wonder if connecting my 3 House batteries to the Accessories battery is a good idea?
Your thoughts please.

 

[Bessy765]

The thing about batteries is how many and how you will charge them. At best most motorhome makers do not make any great efforts to accomplish this. The wiring from the split charger is often undersize. so to try and charge somewhere around 400 amps of batteries is a non starter. At best your van would cope with 2 x 120 amps. But would struggle to cope with more.

 

[The Wino]

Is this a home conversion?. I think the house batteries need to definitely be on a separate system to the starter battery. It sounds like you have a lot of battery capacity what are you charging them from?.

 

[nickdrye]

Surely the alternator will attempt to service the charging load pretty evenly across all the connected batteries to the maximum of its ability. ie. if the alternator can produce 100A then crudely speaking, each of the 5 batteries can only receive a proportion of the available current.
I'm suggesting a configuration something like this:

 

[nickdrye]

The idea is that the house batteries may be charged by the alternator when running or by a generator-driven charger built into the inverter. The system has been working well for the past 5 years, albeit it was unwittingly connected to the wrong vehicle battery!

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[cmcardle75]

I have a 2012 Transit (2.4L Diesel Duratorq 115PS). Following some starting problems, I had the battery fitness checked at Halfords, their basic battery tester classified each of the batteries as 'shagged'. I didn't know until now that the batteries were independent of one another and that one is designated as a starter battery and the other is for the vehicle's accessories, learning this caused me to wonder if my installation of additional batteries may have caused a problem.
My additional batteries (3# 120Ahr) are mounted over the back axel and are there to service a couple of inverters and a handful of small 12v DC loads. It turns out that I had connected these three 'House' batteries to the Starter battery so when the Starter battery began to fail it resulted in the starter motor drawing too much current for the 100A fuses on the link cable.
From what I have read recently, it seems that the vehicle batteries are connected/separated using a split charge set-up so I now believe that I should have connected my House batteries to the vehicle's own Accessories battery.
HOWEVER:
I have to wonder if connecting my 3 House batteries to the Accessories battery is a good idea?
Your thoughts please.

The starter battery is the correct place to connect your array of batteries. However, it needed to be isolated by either a split charge relay (cheap and uncontrolled), or a B2B charger (expensive, but has controlled charging that might charge more quickly and will definitely protect your batteries better). Simply connecting them all together makes a massive starter battery, as you saw when it blew the 100A fuse.

If you connect to the auxilliary battery, you probably get the benefit of the built in Ford split charge relay. However, charge speeds may be very disappointing.

 

[nickdrye]

I think that I could live with disappointing charge speeds. We carry a nice quiet electric start 3.5kw inverter generator and usually switch over after an hour of arriving on site. The house batteries keep the inverters running whilst we are on the move to keep the computers and equipment battery chargers running. I just wish I hadn't installed the bulkhead when we fitted it out. now there is no chance of a cuppa on the hoof!

 

[VXman]

I guess there are lots of different systems, particularly for conversions.

It is normal on professionally built motorhomes to keep the starter battery and the leisure (house) battery (s) separate.

On ours (and most modern motorhomers) charging is managed by the electric control unit (in my case a schaudt elektroblock ebl 119) https://www.apuljackelectronics.co....-Fuseboard-with-Integrated-Charger__p-35.aspx

This allows the majority of the alternator power go to the starter battery when the engine is running and only a small amount to the leisure batteries. Once the starter is full more goes to the leisure. When hooked up on EHU it is reversed with just a trickle charge to maintain the starter and most power going to the leisure batteries. In addition I have a solar panel with is directly charging the leisure batteries.

Another risk you have with your set up of all the batteries linked is running your starter flat if you used too much when camping off grid.

 

[Jamesh]

AFAIK if it's like my mk8 transit the system will charge the starter battery first and then the aux battery.

I'd tie into the aux battery with a vsr / split charge relay whereby the hab batteries only charge at 14.7v when the alternator is running, so that the hab batteries don't discharge the aux batteries.

Btw where are you in Yorkshire?

I'm in Baildon.

 

[autorouter]

The correct place to take a feed for your extra batteries is from the alternator. There is a wire directly from the alternator to the starter battery, so tap into that. The usual place is just as it gets to the starter battery terminal. That's why people say you are connecting to the starter battery, but what you a really doing is connecting to the alternator.

You'll need some device to disconnect the extra batteries from the starter battery when the engine is stopped and the alternator isn't charging. This will avoid the huge starter motor amps surge coming from the extra batteries along the link wires. It also avoids flattening the starter battery if you accidentally flatten the extra batteries.

The traditional way to do this is a relay, triggered by the D+ signal from the alternator. That simply connects the extra batteries, and lets the alternator do its thing of charging all the batteries together. Works reasonably well for a single extra battery, but less well for more than one.

The other way is to use a B2B, which is a proper battery charger that takes its power from the alternator while the engine is running. It will ensure that the extra batteries are fully charged, and not overcharged. A B2B is also called a Boost Charger or DC-DC charger.

If you connect your extra batteries to the auxiliary battery, then all the charging amps will go through its split charge relay, which will probably only be designed for one battery. You are risking burning it out. Better to have a separate split charge relay/B2B for the extra batteries.

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[nickdrye]

VXman, The starter battery is disconnected from the other batteries.
There are two vehicle batteries, one is the starter and the other is the auxiliary, the starter is isolated by a relay when the ignition switch is off. The Auxiliary battery then takes care of all the vehicle accessories. When the engine is running (so the ignition switch is on and the alternator is running) both batteries are being charged. However, I do not know if there is any charge prioritisation going on. The bottom line is that all I am proposing to do is extend the capacity o the Auxiliary battery by adding a few more Batteries so that the domestic capacity is substantial enough to run our equipment. In the unlikely event that I was to exhaust the c.400AH capacity of the non-starter batteries, the starter battery itself would still be isolated and charged ready to turn the engine over.

 

[nickdrye]

If you connect your extra batteries to the auxiliary battery, then all the charging amps will go through its split charge relay, which will probably only be designed for one battery. You are risking burning it out. better to have a separate split charge relay/B2B for the extra batteries.

If the Ford relay simply connects/disconnects the auxiliary battery for charging then I would expect it to be comfortably capable of carrying more current than the alternator is capable of generating... otherwise it wouldn't be fit for purpose!
Additional batteries will not increase the alternator's ability to generate current. I just hope that the magic in the black box chooses to charge the starter battery before charging the auxiliary battery/batteries!

 

[autorouter]

We carry a nice quiet electric start 3.5kw inverter generator and usually switch over after an hour of arriving on site. The house batteries keep the inverters running whilst we are on the move to keep the computers and equipment battery chargers running.

So are the batteries connected to the generator/inverter, so you can have mains power from the batteries while the generator is switched off? I don't know much about generator/inverters, is that usual with all of them or is it a special brand/model that does this?

 

[nickdrye]

So are the batteries connected to the generator/inverter, so you can have mains power from the batteries while the generator is switched off? I don't know much about generator/inverters, is that usual with all of them or is it a special brand/model that does this?

Our genny is an inverter generator, it has nothing to do with the Inverters in the van, the inverters in the van get their power from a bank of batteries.
Our inverter generator is a stand-alone unit which has an inverter that gets its power from its integrated dynamo/alternator which is turned by a c.300cc Petrol engine. The reason we use an inverter generator is that it produces 3.5Kw of well-regulated pure sine wave electricity with a nice quiet petrol engine which is good for sensitive electrical equipment and my ears respectively.
We have two inverters in the van, one is a 3.5kw pure-sine, the other is a 4kw pseudo-sine (basically a form of a square wave), the crappy one is usually only used to boil the kettle or run a drill etc.
We can run the van's pure-sine inverter on the move, when stationery we can choose to add the genny and turn off the inverter, alternatively, we can use the genny to power the battery chargers.

 

[autorouter]

Our genny is an inverter generator, it has nothing to do with the Inverters in the van, the inverters in the van get their power from a bank of batteries.

Ah, OK, it's an inverter generator and a separate inverter with a battery bank. I have a Victron Multiplus inverter/charger, where the charger runs from the mains supply. I thought for a minute someone might have invented a similar thing, like a power pack with a built-in gennie. Oh well, maybe next year...

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[andy63]

for what its worth I would leave the ford batteries as they are and install your hab batteries as a separate set using a battery to battery charger or as I did on my transit conversion a large 100amp blue sea dual sensing voltage relay to charge the hab from the alternator ..
the ford twin battery system I thought was excellent..as you say they are isolated when the engine is shut down but are connected when the engine is running... ford supply a couple of 60amp fused feeds on the back of the seat plinth to allow the user to connect loads to their aux battery,( can be seen in attached photo ) but again if you are installing your own hab batteries you most probably won't need to use them ..
a picture of my battery set up in my last transit conversion..