split charge solenoid or diode? - Horizons Unlimited

**Chris Scott** · #1 30 Jan 2004

What's more common among you lot?

Chris S

**Robbert** · #2 30 Jan 2004

I've solenoid. No probs so far (4 mnths on the road now)
Other set up's I've seen are gismo electronics with lots of LED's and problems, or just an Isolator switch (problem free)

**diesel jim** · #3 2 Feb 2004

i have a different route to this... i run a 300Tdi with twin alternators and twin batteries. that way my auxiliarry battery (runs my winch) is totally separate from the main vehicle electrics.
i have a link switch to join both batteries together for a "double" boost, plus if either of the alternators dies then i can link them and charge both off of the remaining one.

**SandyM** · #4 2 Feb 2004

Yours sounds a nice complete solution, Jim. What better place to carry a spare alternator than in situ?

I had a solenoid type split charge circuit, but it started to give trouble, so I reverted to a heavy-duty (manual) battery switch.

I think my split-charge system was badly designed. It consisted of a solenoid that connected the two batteries together when the engine was running (thus charging both batteries), but otherwise separated them (thus discharging only the secondary battery, to which a winch, fridge etc. might be connected).

The snag was that the solenoid could only handle a continuous 30 amps or so. Fine for charging, of course, but if you operate a heavy current accessory like a winch while the engine is running, the solenoid might allow several hundred amps to flow from the primary to the secondary battery.

I don't have an electric winch, but I am pretty sure that using my air compressor with the engine running was responsible for frying my split charge solenoid.

I don't know about solid-state systems, but I would guess they would work (and maybe fail) in the same way. If I wanted an automatic system again, I would use a solenoid type, but with a BIG solenoid.

Michael...
www.expeditionoverland.com

**Jabbawocky** · #5 2 Feb 2004

I have spent quite a long time looking at this one, as I require quite a bit of power for the fridge and the eberspacher. It seam that the best option is to look at the systems used on emergancy vehicles. These are mostly marine systems, that sence the amps going into the battery and then control the alternator to make sure the batteries are fully charged. Vehicle alternators sence at the alternator and this means your batteries are normal only 75% charged. if you use a diode, this will be even lower. using an altenator controler gets around the problem of the voltage drop caused by using diodes and can increase battery power by 50%. I have no experience of any of the products on the market and there ia a large difference in price, from £150 to £500. Some are use on military vehicle, so they should be up to the job we want to use them for. Type 'Split Chargers' in to your search engines and find out for yourselves.

I am very interested to know if anyone has an experience with these units in their vehicle.

Cheers Mick

[This message has been edited by Jabbawocky (edited 02 February 2004).]

**Sam Rutherford** · #6 2 Feb 2004

I use a marine 4 option rotary switch.

Batt One
Batt Two
Both
None

Easy. Also, on None, the engine won't start - basic anti-theft.

About GBP30 from any chandler.

Sam.

**Robbert** · #7 2 Feb 2004

Yep,

I have a 75amp solenoid which is switched by the alternator, and no winch to melt it down.

Sams switch is the coolest, but my fancy disco dash doesn't like em.

Rob

**ollieholden** · #8 5 Feb 2004

Err, I've often thought I was missing the point on this. I've run the last two Landies with twin batteries with a simple Lucas split charge relay, with no issues. I can't remember the voltage drop but it wasn't much. Dead simple, not much to go wrong in terms of the relay itself. Am I missing something??

**Chris Scott** · #9 5 Feb 2004

Am I missing something??
Utter reliability so there is no chance of flattening 2 bats by mistake or finding a 2nd flat when yoiu need it - I've heard complaints about split chargers doing weird stuff - esp when fridges etc are involved - and was curious
I choose solar charge for the second bat and buy long life milk.

Ch

**Bundubasher** · #10 5 Feb 2004

I also have a Lucas split charge relay in my 4Runner - and although they have been called "spawn of the devil" by another overlander - I have had no problems with it. If there was a problem how would it present itself? (Other than flat batteries)

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Enzo
BUNDUBASHER.com

**Roman** · #11 6 Feb 2004

Hi all,

A diode is the worst possible solution as it causes a 0.8V drop in the charging circuit, so the battery connected through a diode will always be undercharged. A relay won't cause this problem - it allows two batteries to be separated, but it's use is limited. Also, as it is meant to charge both batteries equally - when you switch the ignition key it causes the charge from the good battery to flow back into the discharged battery before both can be recharged from the alternator. A proper split charging system will prevent this as it senses the capacity of each battery and acts accordingly.

I have a Hellroaring system I can highly recommend (I also had one in the Disco). It has one more very useful function - it allows two batteries to be combined. Hence one battery acts as the all purpose battery, the other as a backup. When the main battery is too low to turn the engine, with a remote switch both batteries are paralleled for a short while, then the split charger takes over. Only when the main battery is fully charged, the second battery will receive charging current. Of course you could try to emulate this with a manually controlled relay, but the split charger does the job more safely, accurately and completely automatically.

Any one interested in a split charging system as above implemented in a 12V/24V Landcruiser HDJ80 (with two batteries fitted as standard to run a 24V starter motor), please chack this link: http://www.adgy62.dsl.pipex.com/publ...t_charging.pdf

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Roman (UK)
www.overlandcruiser.info

**Chris Scott** · #12 8 Feb 2004

Hi Roman, have you had to fit 2 of these HR gadgets in parallel, as they recommend for diesels? Seems like an and expensive way of doing it.

Ch

**Roman** · #13 9 Feb 2004

Quote:

Originally posted by Chris Scott:
Hi Roman, have you had to fit 2 of these HR gadgets in parallel, as they recommend for diesels? Seems like an and expensive way of doing it.

Ch

Chris,

No, one split charger unit per side is enough, because in a 24V starter system each battery outputs only half of the cranking current. Hence the cost of electronics was the same as for a diesel engine with a 12V starter motor.

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Roman (UK)
www.overlandcruiser.info

**andybee** · #14 13 Feb 2004

Hi - I like the Hellroaring split charger idea, but my Land Cruiser is 24 volt all round. Does anyone know if you can get 24v split charge units, or whether it is possible to do something reliable and relatively simple with 2x 12v ones? Clearly, any such option involves a total of 4x batteries, but this is the same as Roman's solution for his 80 - so must be 'physically' achieveable.

cheers - Andy