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Snagger

Twin battery, twin alternator vapour build

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...just to add a few notes to the video as the forum software wouldn't let me;

Chronologically stepping through:

  • You can see the fridge is running (-4.3A)
  • When I turn the ignition on the heater fan is running on low and the MS wakes up and primes the fuel pump (-11.5A)
  • When the fuel pump is primed we drop back to -3.8A to spin the heater.
  • You can see the starter current (-225A)
  • Once started, the alternator comes up to 14.1v and the starter battery replenishes (30A) - you can see how quickly this drops off to almost nothing too.
  • Once the main battery voltage has been stable for a few seconds the split charge kicks in and 41A flows into the "house" battery. Bear in mind this is an AGM starter-type battery so will accept a lot more amps than a caravan battery.
  • With the split charge in and the starter battery still replenishing, the total current is 14A + 41A = 55A
  • By only 30 seconds in, the main battery is down to 5A and the house battery is drawing 26A and both are still tailing slowly off.

That video shows a fairly typical start after a day of sitting around with the fridge running.

You can see how the alternator voltage dips a tad under the load, that's the regulator doing its thing as it can't sustain full amps at tickover - but if it was struggling the battery light would be on & the voltage would be down to 12v not 13.8. There's also clearly some losses in my wiring / inaccuracies in the reading but the broad picture is correct.

I will say that I have seen that AGM battery draw 80A very briefly and 50A for a period of maybe 15 minutes after a particularly hard thrashing but your alternator will regulate things the same as mine, dropping the charge voltage a tad until the draw is sustainable. And, again, most leisure batteries won't take 50A+ out of your alternator.

Another thing to note is how quickly the charging currents taper off - the main battery is down to 4A by the end of the video and the house battery is down to 24A already - it's not accurate to just do amps * hours for recharge times but driving for half an hour or more is certainly going to put a hell of a bulk charge back.

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Wow!  That main battery draw drops much faster than I would have expected after starting - I thought it’d be at 10-15a for up to ten minutes.  Very useful.

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I like that guage FF !

Mo

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The Thor engine has a 150 amp alternator, AND on the V8 its nice and high up, out of the way, probably the only good reason to have a Rover V8 :ph34r: Freelander TD4 also has a 150amp unit, but with a different mounting arrangement.

To my simple mind, would make more sense to avoid the complexity of two alternators, and have a solar panel or two instead.

Or maybe a little generator, which is very useful for other things too.

I drove my Renault Master back from Cumbria to Kent at night with a genny running in the back after the alternator died on the way up.  

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17 hours ago, Mo Murphy said:

I like that guage FF !

Mo

If enough people liked it enough to spend ~£200 on it I'd make a run of them. It does two batteries, true voltage & current readings up to 1000A.

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Thanks fridge, I suppose it's not that bad a price as it does amps too.

What size is the finished article ?

Mo

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5 hours ago, Mo Murphy said:

What size is the finished article ?

52mm :D

20190912_164938w.jpg

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Blimey have you mounted yours in an ashtray !

Mo

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9 hours ago, Mo Murphy said:

Blimey have you mounted yours in an ashtray !

Nope, that's the housing, I did it on the lathe for the prototype, didn't have the heart to paint it black!

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I run 2 65 amp alternators on my 110, and I just use an ignition live, through the 24volt warning light on the dash to the 2nd alternator to excite it. 

Perk of 2 alternators is you just keep driving when one breaks. Theres many ways of charging batteries in a vehicle but I see a pair of alternators the easiest to obtain spares for in the wilderness, hence why I chose that route.

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1 hour ago, vulcan bomber said:

I run 2 65 amp alternators on my 110, and I just use an ignition live, through the 24volt warning light on the dash to the 2nd alternator to excite it. 

Perk of 2 alternators is you just keep driving when one breaks. Theres many ways of charging batteries in a vehicle but I see a pair of alternators the easiest to obtain spares for in the wilderness, hence why I chose that route.

That was one of the big attractions for me.  Charge rate of relatively cheap and low rated units so that a short drive would be enough for full charge, near complete separation of the two systems and built in redundancy.  At work, I have 10 generators, including backups, and the new model will have at least two more! 😄

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6 hours ago, Snagger said:

That was one of the big attractions for me.  Charge rate of relatively cheap and low rated units so that a short drive would be enough for full charge, near complete separation of the two systems and built in redundancy.  At work, I have 10 generators, including backups, and the new model will have at least two more! 😄

Dont get carried away wiring them in, just an ignition live off the main loom, to a bulb, to the 2nd alternator. 

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