Vehicle batteries

[Kittyhawk]

Some things are too clever for their own good, as it would seem with the setup on the OPs truck.

Exactly so.
I understand what the designers are trying to achieve with this dual battery setup - having a dedicated cranking battery ensures that there will always be sufficient power in it to start the truck. Instead of two batteries I would infinitely prefer one large capacity heavy duty start battery a la old school. But no fun in that for an electrical engineer when you get the opportunity to design a highly complex and expensive dual system that no end user understands or wants.

 

[Sideways]

When you run the starter motor, it draws a massive current from the battery and causes the battery voltage to sag while it's doing so. I wonder if the reason for two batteries is related to the size of the truck making this a particular issue while something else essential to starting such as an electronic control unit or even basic electronic ignition needs a full 12V to operate properly.

Trucks normally use 24V and no doubts that will be because bigger engines need more powerful starters and it's preferable to double the voltage than the current. Perhaps your truck is near the limit for reliable starting with a 12V battery and using two separate ones was an easy fix for a design issue caught early on.

 

[Kittyhawk]

When you run the starter motor, it draws a massive current from the battery and causes the battery voltage to sag while it's doing so. I wonder if the reason for two batteries is related to the size of the truck making this a particular issue while something else essential to starting such as an electronic control unit or even basic electronic ignition needs a full 12V to operate properly.

Trucks normally use 24V and no doubts that will be because bigger engines need more powerful starters and it's preferable to double the voltage than the current. Perhaps your truck is near the limit for reliable starting with a 12V battery and using two separate ones was an easy fix for a design issue caught early on.

Something I should clarify.
In my 60's the child bride pointed out that I was bored in my retirement and that I should find something meaningful to do. I am grateful for her pointing out this discrepancy as I was obviously labouring under the delusion that I was totally happy pottering about in my workshop. As a result I went back to school and retrained as a front line EMT with our ambulance service. One tends to pick up words here and there and I suppose 'ambulance' is a bit of a mouthful because our vehicles were invariably referred to by staff as 'trucks'. I'm afraid the terminology stuck. What I have been referring to as my truck in these posts is in fact a long wheel base Ford Transit diesel van.
I apologise for giving the wrong impression.

 

[Jameshow]

When you run the starter motor, it draws a massive current from the battery and causes the battery voltage to sag while it's doing so. I wonder if the reason for two batteries is related to the size of the truck making this a particular issue while something else essential to starting such as an electronic control unit or even basic electronic ignition needs a full 12V to operate properly.

Trucks normally use 24V and no doubts that will be because bigger engines need more powerful starters and it's preferable to double the voltage than the current. Perhaps your truck is near the limit for reliable starting with a 12V battery and using two separate ones was an easy fix for a design issue caught early on.

I think in mine it's Done for the rear lights, a/c, step etc that's fitted to my ex minibus. .

 

[glenfield2]

Don’t know if it’s of any relevance but like most canal boats and camper vans we have separate starter and leisure 12v circuits (basically so you don’t flatten your start battery by over-using domestic stuff - you can’t bump start a boat) with a split charge relay.
Ours also has an emergency ‘start assist’ (there are various off the shelf types) which lets you link start and leisure circuits together if a tired start battery needs a boost.

 

[MikeJhn]

I find this all rather strange for what is a 2013 Ford Transit Mk.7, 2.4L turbo diesel van, my 2014 3.0L turbo diesel BMW has only one battery and has never let me down in the ten years I have owned it, can't understand why the battery demand on the said vehicle is so high, I can only think Ford envisaged the van area being fitted out with lots of lights and equipment putting a greater demand on the battery system when stationary.

 

[Stuart Moffat]

Similar frustrations on my Toyota hybrid Auris. Twice I’ve found myself with a car that’s got fully charged batteries with several hundred volts of kick behind it, but with a flat 12v battery cos I left something turned on. It needs 12v in order to boot up the electronics. No way to borrow a bit of the motor batteries!

 

[Jameshow]

I find this all rather strange for what is a 2013 Ford Transit Mk.7, 2.4L turbo diesel van, my 2014 3.0L turbo diesel BMW has only one battery and has never let me down in the ten years I have owned it, can't understand why the battery demand on the said vehicle is so high, I can only think Ford envisaged the van area being fitted out with lots of lights and equipment putting a greater demand on the battery system when stationary.

I expect it's a common architecture not just for ford vans but Peugeot / fiat etc.

And to cover all scenarios too including ambulances, welfare vans, utilities vans etc...

 

[John Brown]

Similar frustrations on my Toyota hybrid Auris. Twice I’ve found myself with a car that’s got fully charged batteries with several hundred volts of kick behind it, but with a flat 12v battery cos I left something turned on. It needs 12v in order to boot up the electronics. No way to borrow a bit of the motor batteries!

My wife had an Auris Hybrid, nice car, but when the 12v battery went flat, you couldn't even charge it in situ. As soon as the battery voltage reached a certain point, it would try to fire up the car, and immediately use all the juice the charger had just put in. Only way was a jump start.

 

[Spectric]

When you run the starter motor, it draws a massive current from the battery and causes the battery voltage to sag while it's doing so.

On older diesels with the big starter motors that could be true but they now use smaller starter motors with epicyclic gears as it works out cheaper, smaller cables and battery.

 

[David Lloyd]

Exactly what I do with my Cherokee, and caravan. Just make sure the panel is connected via a suitable regulator. I just have a roughly 18x6 inch panel which rests on the jeep dash, the caravan has a slightly bigger one permanently installed on the roof. I think go outdoors etc now sell ones with a built in regulator.

I used to compete in off road 4x4 trials in a home built special, the events were monthly and the trialler sat outside my workshop for 353 days a year. I had a chep solar charger from Halfords and that kept the battery, that came from a scrapyard, charged up enough to start the engine every time for over 4 -5 years.

 

[stefan szoka]

Don’t know if it’s of any relevance but like most canal boats and camper vans we have separate starter and leisure 12v circuits (basically so you don’t flatten your start battery by over-using domestic stuff - you can’t bump start a boat) with a split charge relay.
Ours also has an emergency ‘start assist’ (there are various off the shelf types) which lets you link start and leisure circuits together if a tired start battery needs a boost.

Out for a sail this week and one of my crew mentioned that a local lifeboat battery was down on charge with emergency callout. So they bump started it sliding down the slipway with engine in gear and when the prop hit the water it started !!

 

[Inspector]

Something I should clarify.
In my 60's the child bride pointed out that I was bored in my retirement and that I should find something meaningful to do. I am grateful for her pointing out this discrepancy as I was obviously labouring under the delusion that I was totally happy pottering about in my workshop. As a result I went back to school and retrained as a front line EMT with our ambulance service. One tends to pick up words here and there and I suppose 'ambulance' is a bit of a mouthful because our vehicles were invariably referred to by staff as 'trucks'. I'm afraid the terminology stuck. What I have been referring to as my truck in these posts is in fact a long wheel base Ford Transit diesel van.
I apologise for giving the wrong impression.

Is your "truck" the motorhome you were traveling around in last/earlier this year? If so perhaps an RV dealer has a trickle charger kit that can be installed that you can use when it is in storage. You could always copy it if it is spendy and have a look at the parts.

Pete

 

[okeydokey]

Out for a sail this week and one of my crew mentioned that a local lifeboat battery was down on charge with emergency callout. So they bump started it sliding down the slipway with engine in gear and when the prop hit the water it started !!

Surely not - its not April 1

 

[Kittyhawk]

Is your "truck" the motorhome you were traveling around in last/earlier this year? If so perhaps an RV dealer has a trickle charger kit that can be installed that you can use when it is in storage. You could always copy it if it is spendy and have a look at the parts.

Pete

Yes - same vehicle.
I have a nice little 3 stage easily portable charger. The problem was that the two start batteries required a disassembly of the drivers seat to get access. The cranking battery had testing/charging terminals outside of the battery box but the auxiliary start battery didn't but I have fixed that now with a bit of a simple wiring installation so don't need to pull things to bits any more.

 

[Kittyhawk]

Out for a sail this week and one of my crew mentioned that a local lifeboat battery was down on charge with emergency callout. So they bump started it sliding down the slipway with engine in gear and when the prop hit the water it started !!

I can't verify it but a trawlerman pal told me a similar story. Being weather bound in a remote anchorage, one of the boats got a flat battery. She was towed fast by another and the engine started. Trawlers generally have large props turning through a 2 - 3:1 reduction gear and I can imagine that getting the prop rotating by towing and then dropping in the engine decompression levers would get her going. Perhaps the same with the lifeboat.