12V split charge system ideas

[normspanners]

That is purely because the resistance of the front to back cable comes into play. Two identical batteries connected in parallel, with equal length cables will behave as one large battery and charge to the same level.

Not allways I tried that as well and still the batteries are never identical and you will always get a more dominant battery

 

[normspanners]

I never had this problem in my cars years ago with batteries in the boot for big ICE installs

Well it is a problem that even specialists struggle with !!

 

[123hotchef]

Well it is a problem that even specialists struggle with !!

i did not realize it was so complex

 

[rtbcomp]

...
that is the problem !! the low battery will not charge properly, because the higher voltage battery will control the charge !! that is why trucks have problems with the first battery that a radio is connected to, even in a 24v system because just a radio will drop the voltage enough to prevent the battery from charging correctly

The alternator voltage output is constant (as near as matters) regardless of current draw** due to the regulator, so you'll have (say) 14v across both batteries. Each battery will take the current it requires to charge it, irrespective of what else (batteries, lamps &c) is connected to the circuit.

** In exceptional cases the alternator voltage will drop to limit the current to a safe level, but if this needs to happen you've a fault that needs fixing

 

[armalites]

If you want the best setup you have to spend some proper money on something like a CTEK DC-DC charger, that the primary is charged as normal and the secondary is then charged by what is just a DC powered battery charger so does a proper job even on a heavily discharged battery.

 

[rtbcomp]

...still the batteries are never identical ...

In that case that's what's causing the problem, not one battery having less charge than the other.

 

[scotb]

fit a merlin smartbank, and a merlin battery guard on the chassis battery.

 

[normspanners]

there is forumula ie peukerts equation sometimes called the 'shrinking battery effect'

In that case that's what's causing the problem, not one battery having less charge than the other.

sorry but you are wrong,they dont charge properly because there are three stages of battery charge, and different batteries could be at differnt stages of charge, that is the problem you only have to look at peukarts equation sometimes called the shrinking battery effect

 

[armalites]

The alternator voltage output is constant (as near as matters) regardless of current draw** due to the regulator, so you'll have (say) 14v across both batteries. Each battery will take the current it requires to charge it, irrespective of what else (batteries, lamps &c) is connected to the circuit.

** In exceptional cases the alternator voltage will drop to limit the current to a safe level, but if this needs to happen you've a fault that needs fixing

Charging on many modern cars is controlled by cars brain and not the alternator and they vary the voltage to suit conditions so the voltage output is not constant.

Discovery 4 vary the voltage based on things like temperature/charge/load

 

[123hotchef]

this is not a modern car it is a 2003 pick up

 

[normspanners]

why would the mod spend millions on specialist companieshttp://www.smartgauge.co.uk/index.html
if it was just a matter of simply connecting two batteries together and letting the alternator get on with it ?
ambulances etc all have major problems with this exact scenario

 

[normspanners]

battery charging is a very complex subject hense why cars now have smart charge control

this is not a modern car it is a 2003 pick up

that will not have smart charge but smart charge especially doesnt like twin battery setups because the two batteries are always at different stages of charge.

 

[ajlelectronics]

why would the mod spend millions on specialist companieshttp://www.smartgauge.co.uk/index.html
if it was just a matter of simply connecting two batteries together and letting the alternator get on with it ?
ambulances etc all have major problems with this exact scenario

Because lots of people are earning lots of money from providing a solution to a problem yet to be discovered?

 

[normspanners]

smart charge has a small voltage sensing wire direct to the ecu from the battery that senses millivolt changes in the battery state, so two batteries can never give the same reading

 

[normspanners]

Because lots of people are earning lots of money from providing a solution to a problem yet to be discovered?

Its not yet to be discovered !! I cannot believe you are saying this its been around for years !!

 

[ajlelectronics]

Its not yet to be discovered !! I cannot believe you are saying this its been around for years !!

So have I Norm and I have been in electronics since the early 70s. I have seen all sorts come and go to sort out a non existent issue, including rebodied capacitors and silver mains cable. In order to sell something, you have to show a need. Some salepeople are more skilled than others of course, except where government contracts are concerned of course, where they will just shell out on the flimsiest of "evidence".

 

[normspanners]

Ford have spent lots of time and gone to long lengths to put twin battery setups in modern transits splitting the battery usage and draw and also the way they are charged to help solve this long standing problem

 

[123hotchef]

the merlin smartbank lite does sound like a good solution does it not

http://www.jgtech.com/pdf/SBLitemanual.pdf

 

[normspanners]

So have I Norm and I have been in electronics since the early 70s. I have seen all sorts come and go to sort out a non existent issue, including rebodied capacitors and silver mains cable. In order to sell something, you have to show a need. Some salepeople are more skilled than others of course, except where government contracts are concerned of course, where they will just shell out on the flimsiest of "evidence".

Believe what you will, all I know is twin battery setups do not work effectively and end up costing batteries, in fact all pajerero's and the like, now, I am advising people to do away with the extra battery and fit one larger capacity battery because the batteries are only lasting a short time and end up 'shrinking' in capacity . I have done/modded loads and they have never had a problem after.

 

[rtbcomp]

Charging on many modern cars is controlled by cars brain and not the alternator and they vary the voltage to suit conditions so the voltage output is not constant.

Discovery 4 vary the voltage based on things like temperature/charge/load

I was half expecting that one If that's the voltage at the alternator then they'll have to increase it slightly under high load conditions to compensate for voltage drop along the wiring, so the voltage at the point of delivery is correct. Modern cars also use thinner wire with heat resistant insulation in their wiring to keep cost & **weight down, so voltage drops along the wiring need to be taken into account.

** I can't find it now, but there was a discussion about reducing the weight of wiring harnesses to avoid injuries to the production line workers who fitted the harnesses.