Electrical setup, options and answers, from scratch!

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NeilV
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Electrical setup, options and answers, from scratch!

Postby NeilV » Wed Jul 22, 2015 8:15 pm

Well, no system starts truely "from scratch" as all MH start with a 12 or 24v battery and alternator for their motor...

So after flip/flopping between I'm currently running
My 2x104ah 12v batteries (AASolar) in series as a 24v supply, with a 10A12V 'buck' charger for the thetford toilet, fresh water pump, and 8LED "house" lights (I left most of the 24V bus incandescent/fluorescents in situ as these provide alternative options when driving anyway).
This is not set in stone, as I have only invested $30 in the step down 12-24v transformer- so far...

The Danfoss 12/24v compressor fridge I just bought will go either way, so works just as well (at lower amps=thinner wires on 24v anyway)

I have a quality 3stage dual 24V smart charger (bought for bus batteries when I was living off the original bus wiring/lights alone) which also lend themselves better to the 24v setup too I guess

I have a "free to me" 20A 12/24v PWM solar charger already too, so I'm looking at either one or two (budget controlled decision) 30V solar panels, currently 250W from AASolar work out around $1/W, so excellent value, and better output at 24v (if only 8A out either way anyway?)

I have 2 inverters, an older 600W 12v modular, and a new 24v1200W pure sine also...
Specific questions to follow...
8.5m 1990 Dennis Dart bus, 6L turbo -4 pax
- 24v system: 2x 104ah AGM, 20a PWM controller 500W solar; 1200w puresine inverter
120L grey/fresh water, 75L compressor fridge, gas Califont, Diesel MK85 heater [awaiting install]

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NeilV
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Re: Electrical setup, options and answers, from scratch!

Postby NeilV » Wed Jul 22, 2015 10:11 pm

Charging:

As my smart charge is dual 24v (8A) anyway, this would be suited to permanently be wired to the eventual charging system whenever connected to 24V, and could work well with solar and (either) inverter if needed too?

I chose 24v currently as this slows 'native' charging via the existing alternator when paralleling with bus starter batteries (and lower voltage drop too)

I would expect 250W @30V via the PWM controller to [theoretically] put out (into batteries) 8A [max] ... So 24v@8A is 192W but at 12v is only 96W? Can this be true??
8.5m 1990 Dennis Dart bus, 6L turbo -4 pax
- 24v system: 2x 104ah AGM, 20a PWM controller 500W solar; 1200w puresine inverter
120L grey/fresh water, 75L compressor fridge, gas Califont, Diesel MK85 heater [awaiting install]

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NeilV
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Location: Franklin

Re: Electrical setup, options and answers, from scratch!

Postby NeilV » Wed Jul 22, 2015 10:19 pm

From the refrigeration thread... viewtopic.php?f=102&t=11388&p=96912#p96912

Neddy wrote:This will not enable you to maximise the charging of your House batteries while under way. It is a ut in your case, one method stands out, well ahead of the rest.

You have got a new 24v 1200W pure sine-wave Inverter. All you have to do is plug its output into the 3-stage 24V smart charger that you have already got and the problem is solved. Effectively, elegantly and very, very cheaply. Mad if you don't, really!

Neville.


So I plug my smart charger via the inverter to the starter batteries (as suggested to Mark on HIS fridge thread) and effectively the alternators current somehow is maximised through the use of 2different devices? Shouldn't there be significant losses associated in the 24v-230v-24v conversion???
8.5m 1990 Dennis Dart bus, 6L turbo -4 pax
- 24v system: 2x 104ah AGM, 20a PWM controller 500W solar; 1200w puresine inverter
120L grey/fresh water, 75L compressor fridge, gas Califont, Diesel MK85 heater [awaiting install]

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Re: Electrical setup, options and answers, from scratch!

Postby Neddy » Wed Jul 22, 2015 10:58 pm

The regulated charge voltage of your alternator is relatively low, probably even less than 28 volts. You could have your Smart charger set to as high as 29.8 volts, thus your House batteries get a much higher charging current than your Starter batteries = faster charging for your House batteries (which you want) but not for your Starter batteries (which you don't).

You could estimate the losses incurred by the 24v-230v-24v conversion by simply adding the Inverter loss to the charger loss. You should have access to both of these figures for the models you have got. I would guess that overall efficiency would work out at around 80% or better. Most commercial 24v-24v Even Chargers have efficiencies of around 85% - and cost upwards of $500.

Neil, if you are thinking of (initially) getting just the one 250 watt solar panel, you should do all you can to maximise your alternator based charging.

Neville.

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Re: Electrical setup, options and answers, from scratch!

Postby Neddy » Wed Jul 22, 2015 11:23 pm

"I would expect 250W @30V via the PWM controller to [theoretically] put out (into batteries) 8A [max] ... So 24v@8A is 192W but at 12v is only 96W? Can this be true?"
Well, no, it can't. Controllers are usually quite efficient, so very roughly, Solar Watts in = Maximum Battery charging Watts out. For example, charging at, say 29 volts would give a theoretical maximum charging current of 8.6 Amps. Don't forget though that the batteries state of charge will have a large effect on the charge current, so the actual figure will almost always be way less than that.

Two solar panels of that size would double the theoretical maximum charging current, as would using the same panel to charge a 12 volt battery. The controller sets the charge voltage, and the battery controls the charge current relative to that. Higher charge voltage = higher charge current and vice-versa.

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NeilV
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Re: Electrical setup, options and answers, from scratch!

Postby NeilV » Thu Jul 23, 2015 12:25 pm

Neddy wrote:
Two solar panels of that size would double the theoretical maximum charging current, as would using the same panel to charge a 12 volt battery. The controller sets the charge voltage, and the battery controls the charge current relative to that. Higher charge voltage = higher charge current and vice-versa.


Thanks, thought the math didn't work the way I asked as nobody would have a 12v system if it were so.

Only concern with higher charging on house batteries than charge into starter batteries is the possibility of actually draining the flooded start batteries into the AGM house ones... More out than in while driving AND stupid/tired driver not switching the inverter off when stopping... Ignition based relay? (Now I sound like my Dad :oops: fix anything with a relay!)

Can the 'dual charge' smart charger remain connected to both battery banks when inverter is running from starter batteries charging main like this, would that create a (minor) loop loss, or (major) short circuit issue?
Last edited by NeilV on Thu Jul 23, 2015 12:45 pm, edited 2 times in total.
8.5m 1990 Dennis Dart bus, 6L turbo -4 pax
- 24v system: 2x 104ah AGM, 20a PWM controller 500W solar; 1200w puresine inverter
120L grey/fresh water, 75L compressor fridge, gas Califont, Diesel MK85 heater [awaiting install]

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NeilV
Posts: 1139
Joined: Fri Apr 17, 2015 6:49 pm
NZMCA No: 60322
Location: Franklin

Re: Electrical setup, options and answers, from scratch!

Postby NeilV » Thu Jul 23, 2015 12:41 pm

On to 240v system...

So given I have actually somewhat committed to 24v by buying the charger and better inverter at that voltage ...

Wiring the 240v system ideas are currently:

1) 16A 'shore power' caravan plug and adapter from "shore" to enter just above drivers window, into breaker box, and off to 4-6 plugs evenly balanced along each edge of the bus

2) inverter circuit (now needed 'from' house batteries?) to main breaker box on a (want relay *sob*) switchover required whenever shore power not available and 240v desired
(user decision not to use micro or oven when on inverter-not plug dropped from circuit, also compressor fridge 24v native negates need to drop plug out)

3) (?) circuit to switch inverter from start batteries to house batteries and drop out charger when NOT on 'shore' power... Manually plug juggling not desired!

240 Plug points:
-smart battery charger to (dual charge?) house and start batteries
-kitchen 'benchtop'
-and opposite for micro/tabletop oven,
- bedside double(?) plugs at roof night over windows and curtains at each side of rear island bed (maybe?) 12v/24v ciggy plugs here for phone charging too (though your charging thread post makes this redundant if 240 inverter is available anyway?)
8.5m 1990 Dennis Dart bus, 6L turbo -4 pax
- 24v system: 2x 104ah AGM, 20a PWM controller 500W solar; 1200w puresine inverter
120L grey/fresh water, 75L compressor fridge, gas Califont, Diesel MK85 heater [awaiting install]

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Re: Electrical setup, options and answers, from scratch!

Postby Neddy » Thu Jul 23, 2015 12:55 pm

"Only concern with higher charging on house batteries than charge into starter batteries is the possibility of actually draining the flooded start batteries into the AGM house ones... More out than in while driving."
That's never going to happen. The alternator will continue to churn out the same fixed charge voltage that it always has, resulting in exactly the same charge current for the Starter batteries regardless of whether the 24v Inverter/Charger is turned on or not. As far as the Starter batteries are concerned NOTHING has changed.

"Stupid/tired driver might forget switching the inverter off when stopping"
There are several ways of circumventing this potential problem. The simplest alternatives would include :-
(1) As your Dad might suggest, an ignition based relay would do the job well.
(2) Fit a VSR (Voltage Sensitive Relay) That would work even better.
(3) Install the equivalent of a headlight warning buzzer. If the Inverter is on and the Ignition is off, it sounds.
(4) You could do as I have done and link the manual Inverter On/Off switch to a really bright indicator light.

If you expect to hardly ever use this system, Option 4 is best. If you want it to run every time you run the engine, option 2 would be the best way to go.

Neville.


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