split charge system

[georgeh]

Hello,

Can anyone clarify / explain 2 things about / to split charge systems for me please?

Do they prevent one battery running down whilst using ancillaries with the engine turned off? Do they prevent the voltage equalisation that occurs when connecting two batteries together, for example while starting?

If I run the low voltage feed to the relay from the charge warning light in the dash, then this connects the two batteries when the light is on, i.e. the instant the ignition is turned on, which is bad because the voltages will then equalise with the possibility of leaving me with not enough volts to start.

I know i'm getting confused, but can someone help??

Cheers,
George

[jota]

have a look here for some info on dual battery setups and battery isolators.
I have the BIC 85300A on my 4x4 van and it has been great.
http://www.hellroaring.com/

Basically, all acessories are connected to my main battery that is charged by the alternator when the engine is running. The auxillary battery is connected to the isolator/ combiner and also gets charged by the alternator when the engine is running so it stays always fully charged. When my main engine battery gets drained, I switch on the isolator to restart the van to get going and can also combine both batteries when using the electric winch for better pulling power.

[Roman]

<font face="" size="2">Do they prevent one battery running down whilst using ancillaries with the engine turned off? </font>

Yes
====

<font face="" size="2"> Do they prevent the voltage equalisation that occurs when connecting two batteries together, for example while starting?[/B]</font>

Yes

N.B. If split charging could be achieved with five quid relay, there would be no market for electronic gadgets costing 100 quid, such as Hellroaring. The Hellroaring BIC, being an isolator/combiner, also allows you to switch between two modes, with current flowing either towards the isolated battery (only after the main battery has been brought up to full charge), or current flowing both ways, when you need to boost the main battery from the second battery.



------------------
Roman (UK)
www.overlandcruiser.info

[Jose Brito]

Hi,

I have an IBS dual battery system with a battery monitor: http://www.ibs-tech.ch/dbs_e.html

With such a device you can connect/disconnect batteries, when using whinch, fridge, and other electric devices, and at the same time, monitor the both battery levels. It also indicates the charging level produced by the alternator, when the car is moving.

Until, I consider it very reliable and easy to use. The downside is the price....

Cheers,
José

[Sam Rutherford]

I have a split-charge system, but don't trust it when solo in the middle of nowhere.

On my 'starting' battery, I have a big switch on the earth. Once stopped, I turn 'clunk' the switch and no matter what, it's going to be good when I want to start the engine again.

Simple works...

Sam.

[georgeh]

Sam,

that is along my lines of thinking. is your split charge system one of the expensive packages that the other posters are discussing? I can't afford one of these and am trying to come up with a good, simple alternative that i understand and can fix / alter as i see fit.

The simplest would be to have 2 isolator switches - one on each earth and then swap the batteries over as you like for charging / draining but this is too prone to human error for me, the chances of accidentally connecting the 2 batteries and draining the starting one is too high.

i've tried to find a big on-on switch so the 2 can never be connected at the same time, but to no avail. does anyone know where i might find one of these rated to the required curent (300A? i have no winches or anything else that draws massive current).

Failing that, a smaller on-on switch (5-10A) and 2 relays would do the job but the relays still need to be rated high. What is the best relay to use for this? I was thinking maybe a pair of remote start solenoids like the ones originally used on series landie engines..

[Roman]

georgeh,

"...but this is too prone to human error for me, the chances of accidentally connecting the 2 batteries and draining the starting one is too high."

Well, the expensive packages are there to save you from exactly the problem you mention. If you want a simple A - B - A+B switch, you can get them from boat chandlers. An ON-OFF switch can be of the type used to disconnect batteries in emergency. Any car accessory shop shuld have them. Also, you can use an 70amp+ relay. Check the Vehicle Wiring Products website.

------------------
Roman (UK)
www.overlandcruiser.info

[Robbert]

For no winches...

I have a 75amp relais switched by the alternator. As soon as the alternator starts delivering current (i.e. the engine is running) the batteries are connected. Easy, simple and cheap, but not up to winching.

Rob

[Roman]

Originally posted by Robbert:
Easy, simple and cheap, but not up to winching.Rob

Robbert,

If you configure the circuit as for Starter/House batteeries, the switch is for charging, not winching. The winch and any other auxilliary loads need to be connected directly to the second battery. You don't want to combine two batteries for winching and drain both, do you?

In the Main/Backup configuration the main battery is used for all jobs and only when it becomes drained, you combine two batteries to boost the current needed for starting. A 75-100A rated switch should suffice, as the backup battery is not expected to supply all the current required, and in any case only for a short time.


------------------
Roman (UK)
www.overlandcruiser.info

[This message has been edited by Roman (edited 12 July 2004).]

[Sam Rutherford]

In reply to the earlier questions.

It's a relatively cheap electonic system - hence the lack of confidence.

I also have a 4 way switch from a Boat Chandlers, to allow more control both for discharge and charge. Regardless though, is the 'big switch' for the main battery. When I'm stopped, it goes off. No matter what else happens, the engine will start again when I switch on and turn the key.

Sam.

[Robbert]

Roman,

I never considered a winch, so didn't realy look into it, but, when winching with the engine running, both batteries will be connected and when the aux batterie is getting low, the current trough the relais might get to high. I can imagine other switches controlled by the winch braking the connection etc... . Way to complex to run a fridge....

Rob