Club 80-90 Forums

As part of an electrics redesign I'm doing, I want to have a circuit that's only active when the engine (i.e. alternator) is running. The right way to do this would be to have a diode downstream of the alternator, and then tap this circuit in upstream of that.

Anyone know if there's already a diode for this in the 'standard' wiring?

(Basically I have a bunch of rechargeable 'things'. Left idle, they go flat. Part of my new design is to take the 'thinking' out of charging. I'll also need to put the output from the solar upstream of this diode too.)

have a relay off the ignition circuit ? then when ignition on relay energised and stuff can charge

jamesc76 wrote:have a relay off the ignition circuit ? then when ignition on relay energised and stuff can charge

+1

Basically, use the second relay type shown under 'split charge relays explained'. You don't have to use it for split charging but you can use blue wire from alternator to trigger it. https://club8090.co.uk/wiki/Ca ... it_charger" onclick="window.open(this.href);return false;
As said, relay is the answer.

jamesc76 wrote:have a relay off the ignition circuit ? then when ignition on relay energised and stuff can charge

I did ponder that, then remembered... Solar.

Basically there's a few times a year I'm properly off-grid, static for a week or two at a time, and want the solar on equal footing with the alternator, I.e. If it's making juice, I want that to go into the main battery and my charging circuit (unattended like ).

Now I've found a suitable diode easy enough - there's an inline 12v 50a off the shelf component. But having just done an initial reccy on the wiring in the engine bay, I fear this might be a bit more hassle than I imagined. Possibly need to run a new feed from the engine bay to the battery box in order to isolate the alternator via the diode. Hmm. Time to dig out circuit diagrams.

So, here's the schematic for my crazy electrics plan...

The design here is to cover three scenarios:

Standard - extraneous gumph like charging etc is limited to alternator / solar only. Just core stuff + lights + stereo gets battery power. Basically, avoid running battery flat when parked up, especially if solar is doing chuff all, as indeed it might for long periods during the winter.

Battery - let rip. Everything can chew at the battery if it needs to, but will also take from solar or alternator if they're makin' bacon. 240v sockets limited to inverter power (no heaters, kettles, cement mixers etc)

Hookup - flip everything over to external mains. 240v sockets can let rip within the hookup limit. Not just for campsite use, also for driveway... 12v batteries charged from hookup. If the hookup falls over, most stuff won't failover to battery, apart from lights and stereo.

https://docs.google.com/drawings/d/1wIf ... M9c2I/E D I T" onclick="window.open(this.href);return false;

I think I'll need to tweak this to stop the inverter low voltage alarm going off in unintended scenarios. And it's also vaguely possible that I don't need the diode if I put a chunky solar regulator in it's place.

Is this all a bit over the top? Completely.

Pretty diagram.....couldn't make head nor tail of it but pretty all the same.

My advice to you....don't re-invent the wheel....all the solutions to your particular needs are out there and available off the shelf.

Martin

If you use a voltage sensing relay and have the solar charging going to the starter battery - just recharge your items from the leisure side. That way everything receives charge from both solar and alternator. (+ hookup if you charge the vehicle battery whilst hooked up). You do seem to be overcomplicating things somewhat!

California Dreamin wrote:Pretty diagram.....couldn't make head nor tail of it but pretty all the same.

My advice to you....don't re-invent the wheel....all the solutions to your particular needs are out there and available off the shelf.

Martin

Yep - anything where I can use off the shelf parts, I will. All suggestions welcome.

Oldiebut goodie wrote:If you use a voltage sensing relay and have the solar charging going to the starter battery - just recharge your items from the leisure side. That way everything receives charge from both solar and alternator. (+ hookup if you charge the vehicle battery whilst hooked up).

Do you mean the solar solely going to the starter?

A *key* requirement is to be able to live off the solar ad-infinitum. The longest stint of the year is usually about two weeks. No driving, no engine running, no hook up. Fully off grid. My panel worked brilliantly for this last year, I'm just trying to (with some complication indeed!) make it slightly easier to manage.

So err, yeah, my needs are a bit unusual. But that's not to say there isn't a better way of implementing it - all ideas welcome.

(The "charging circuit" idea is one of convenience, not really necessity by the way. If it wasn't for the solar in the equation, James' suggestion about running off the Ignition would have worked perfectly.)

If the solar panel feeds the starter the voltage sensing relay takes care of charging the leisure. Of course it will not be putting much into the starter if there is no drain on it as there shouldn't be if you have everything run off the leisure. I have done mine that way as I can cope with a flat leisure battery if I am out in the wilds of Scotland but I want to ensure that I can start the van. You always have the option of running the engine if the leisure is flat and it has p***ed down for a week, it is hard to do anything if you have flattened your starter. I have always wild camped so never see a hookup. Six weeks around Scotland with no hookup - just solar and some driving. What size panel are you using to live off - you may need a minimum of 110/120w depending upon how frugal you are with power and what you are trying to run. I only use a 40w one with 110Ah battery but then I only use a few leds lights,water pump and a bit of radio use. Charging of phones is a minimal drain.
On my Merc I manage with 80w solar and 220Ah of batteries.

Oldiebut goodie wrote:If the solar panel feeds the starter the voltage sensing relay takes care of charging the leisure. Of course it will not be putting much into the starter if there is no drain on it as there shouldn't be if you have everything run off the leisure. I have done mine that way as I can cope with a flat leisure battery if I am out in the wilds of Scotland but I want to ensure that I can start the van. You always have the option of running the engine if the leisure is flat and it has p***ed down for a week, it is hard to do anything if you have flattened your starter. I have always wild camped so never see a hookup. Six weeks around Scotland with no hookup - just solar and some driving. What size panel are you using to live off - you may need a minimum of 110/120w depending upon how frugal you are with power and what you are trying to run. I only use a 40w one with 110Ah battery but then I only use a few leds lights,water pump and a bit of radio use. Charging of phones is a minimal drain.
On my Merc I manage with 80w solar and 220Ah of batteries.

Good to hear there's another odd-ball like me. I'm running a 100w panel.

(Bit sleepy now, will have a proper ponder of your thoughts tomorrow)

Just a quick note from me as most bases seem to have been covered above, but note = you cannot use a diode the way you wish to. Silicon diodes always drop roughly .6 of a volt across them. This would knock the entire feed from your alternator from 13.8 to 13.2 volts = not enough to charge your batteries properly etc.

As above, just use a relay

Not read all the thread but, if required, you can get "solid state" relays with no moving parts who's "trigger" current is minuscule, even micro amps to turn it on = might be of use for long unattended periods...

ghost123uk wrote:Just a quick note from me as most bases seem to have been covered above, but note = you cannot use a diode the way you wish to. Silicon diodes always drop roughly .6 of a volt across them. This would knock the entire feed from your alternator from 13.8 to 13.2 volts = not enough to charge your batteries properly etc.

As above, just use a relay

Not read all the thread but, if required, you can get "solid state" relays with no moving parts who's "trigger" current is minuscule, even micro amps to turn it on = might be of use for long unattended periods...

Ah. Diode voltage drop not good... a flaw in my plan.

Gonna have a look at the voltage sensing relay idea.

if you go the voltage sensing relay way, when you buy one, buy two..(if you have a spare you will never need it kind of thinking)... if they fail while you are "offgrid" they may well connect everything you dont want connected !!! i personally dont trust them. ( Just my experience)