Anyone put a diode in a spit charge system?

[ringo]

In an effort to keep my leisure batteries completely seperate at all times, i have bought a shottky power diode to put in series with my 110 ah battery so that this doesnt discharge into the smaller leisure battery when they are all on charge (via seperate split charge circuits).

My questions is, for those whom remember more than I, will my 110ah battery ever charge because it will always have 0.3V less over it than the other batteries?

Anyone ever tried it?

Regards,

Richard

[1664]

Yes it'll charge up but 0.3v less than the other one given enough time to fully charge them both. I can understand having two leisure batteries as it gives you a lot more leisure capacity but why do you want them seperating rather than using them in tandem? You running seperate bits of equipment off them?

[ringo]

Thanks Bren.

Yes, one battery is for the van electrics (65ah) and the other (110ah) is for the eberspacher. I also want to keep them seperate so they dont drag each other down when one breaks (this has happenned to me twice in seven years).

What i am planning to do, is create a distribution block so i can switch sources. so for example in summer, if the van battery goes low, i can switch it to the eber battery (as i wont be using the eber).

I just had a chat with one of the hardware guys at work and he doesnt even think the diode is necessary as charge wont go from a fully charged 110ah to the 65ah because the alternator will always be higher voltage than the batteries - hence forcing current flow in a charging direction.

Sounds reasonable to me - what do you think?

Thanks,

Ringo

[1664]

I just had a chat with one of the hardware guys at work and he doesnt even think the diode is necessary as charge wont go from a fully charged 110ah to the 65ah because the alternator will always be higher voltage than the batteries - hence forcing current flow in a charging direction.

On paper that sounds right but I'm worried certain senarios may crop up where things might go a bit pear shaped. For instance; what rating alternator have you? Picture the scene where the camper battery and the Eber battery are heavily discharged, you've just started the van (cold day, fair few turns required etc) and you have three batteries plus possibility of headlights, heated rear window, heater blower etc all competing for juice off this poor defenceless alternator. If the Eber battery is more discharged than the camper battery, current will flow between them unless another diode is used with the camper battery. We already know how a flatish battery will drag a hefty current from the alternator until the charge has built up a bit. At best the alternator voltage could drop if it was pushed beyond it's limits, worst; who knows?? (I'm not very 'up' on alternators / voltage regulators)

If it were me, I would have a traditional (but still robust) split charge set up for the starter and camper batteries as per what I have now and I would set up the Eber battery so that it had to be physically switched into the charging system while the (by now fully charged) camper battery was disconnected, by 2 position switch for example although there are lots of ways you could achieve this.

Other folk may have a different opinion on this........

[ringo]

Agreed Bren.

I really would like an intelligent system and i plan to build one one day - but for now it will have to be basic.

The split charge circuits have 30A fuses in them so these should blow if things go breasticles up. Its a 90A alternator so should be up for the job.

Im also struggling with switches - the biggest i can find is a 15A DPDT and i have to connect two poles in parrallel to give me 30A - so i really do need a 30A switch.

I've had the setup without the diode running for years now and i've not had any fuses go yet - i might leave it like it is....

Cheers,

Richard

[jamesc76]

Im also struggling with switches - the biggest i can find is a 15A DPDT and i have to connect two poles in parrallel to give me 30A - so i really do need a 30A switch.

Richard

Might struggle to find anything over 20amp, but with a relay you can switch that with any switch you want?

[ringo]

Yes - i know what your saying but I dont really want to use a relay because of the power drain. I leave the switches in postition for months at a time if not more. Its Rare that i actually switch them unless i have exceptional circumstances like the eber battery has drained and i need to switch it to the camper battery. Its a backup really.

Cheers,

Ringo

[ringo]

This bad boy might do the job

http://cgi.ebay.co.uk/RED-3-WAY-BATTERY ... 53e4e834fa


Its never cheap is it

Ringo

[jamesc76]

what about isolator switches then? ok there big but 2 of um should work?

[jamesc76]

This bad boy might do the job

http://cgi.ebay.co.uk/RED-3-WAY-BATTERY ... 53e4e834fa


Its never cheap is it

Ringo

that will do it plus whilst van parked up for any time you can switch um off completely!

[Mocki]

i used a 40amp 5 pin relay to do this, with the normally closed position when unpowered for the "normal" selection, and it only needed power when in "emergency" mode. WOrked fine, and was no power loss, or drain.
and just used a tiny toggle switch for control.

your mans right about the alternator keeping the batterys seperate, even if the batterys are below voltage. however id be making the control signal for the two split chargers switchable to give the main battery a chance on short drives in winter.
and if the leisure batterys are low, you can switch the signal off to avaoid stupid amps being drawn on start up

[ringo]

i used a 40amp 5 pin relay to do this, with the normally closed position when unpowered for the "normal" selection, and it only needed power when in "emergency" mode. WOrked fine, and was no power loss, or drain.
and just used a tiny toggle switch for control.

your mans right about the alternator keeping the batterys seperate, even if the batterys are below voltage. however id be making the control signal for the two split chargers switchable to give the main battery a chance on short drives in winter.
and if the leisure batterys are low, you can switch the signal off to avaoid stupid amps being drawn on start up

Very interesting that Steve - point taken on board for the split charger signal to be switchable - i will do that.

Ringo

[1664]

I'd be inclined to fit 2 relays with the signal wire being switched - possibly even a 3 position switch. 'Camper', 'Eber', and 'Off' ('Off' in the case of the starter battery getting a sustained hammering due to difficulty starting the van which would make it's recharging a priority). The senario I suggested was an extreme one but not that unlikely an event considering our capacity (and desire) for winter camping these days. Good that you have a 90amp alternator. Yes, your 30A fuses will protect the system but in extreme cases these can blow too. The obvious answer to all this is not to discharge any batteries to such a large extent in the first place but then you can't tell just by looking at them. You've seen them bluddy big fuses I've fitted to mine haven't you?





You could use intellegent relays; one that senses the starter battery voltage and switches the camper battery to charge and one that senses the camper battery voltage and subsequentially switches the Eber battery to charge.

There's all sorts of configurations you could opt for - and on the load side too

[ringo]

Yes, i have those fuses fitted Bren - nicked the idea from you a while ago

For now they are going to stay pretty much as is.

I plan to build a intelligent split charge system based on a PIC processor to monitor the battery voltages and to charge accordingly. First things first though it will just create a switchable system from a LCD menu so i can change which batteries are being charged.

I've been intending to do this for years so dont hold your breath....

Ringo

[jamesc76]

I plan to build a intelligent split charge system based on a PIC processor to monitor the battery voltages and to charge accordingly. First things first though it will just create a switchable system from a LCD menu so i can change which batteries are being charged.

I've been intending to do this for years so dont hold your breath....

Ringo

well if ya do ever make it do me one