Ideal electrical set up???

[trentjim]

Ok so on a WAECO CDF-25 Fridge its between
0.44 Ah/h at +20°C ambient temperature,
...that'll be just over 10amps per hr

no its a shade over 10 Ah per day or to put it another way 50 Ah will see you through the week during the winter which is your pinch point...(caveat - presumably these figures hold true as long as you never open the fridge LOL) work out the heater consumption next... you might be ok on a much smaller battery reservoir

J250p x2 which make 500AH

partially true...they make 500Ah at 6V....
you need 12V therefore two of those will give you 250Ah at 12V

[ghost123uk]

If it is any help re engine power in electrical watts (like for the Aircon consumption) I do know that to produce 750 Watts needs about 1HP of engine power. 750 Watts at 12 volts = 62 Amps

Not sure if that info is any use

[AdrianC]

quite right... quote above was my next post on the thread...

Ah, I missed that one! Sorry...

still havn't been able to find anything reliable to calculate the "fuel consumption" of an idle engine loaded with an alternator pushing 50A or so

Trial and error's probably the best way.

[trentjim]

it did cross my mind to try and work back - but still dont know how many kw the aircon compressor is nor the engine relationship between fuel consumption and work done...

mind you... the low power consumption of the fridge above got me thinking, and once i'd got thinking i had to do some sums....

cooling 1g of water from 20c to 5c takes 15 calories
a can of your finest brewed malted beverage contains 500g of liquid... lets treat it as water from a thermodynamics perspective and ignore cooling the container
to cool our room temperature tipple to a more palatable 5 degrees therefore takes 7500 calories
1 watt for 1 hour = 856 calories

so to chill our can we need an energy input of 8.76 watt/hr
8.76 watts at 12v = 0.73Ah

or to put it another way, according to the laws of thermodynamics chilling a 4 pack uses about 3Ah

this would be based upon 100% efficency in heat transfer, a compressor fridge is usually 30-40% efficient in this regard so lets give it the benefit of doubt and call that 50% efficient...

so its a party weekend... you've got 24 cans to chill, doing so is probably going to leave your batteries 36Ah lighter

to put it another way... anyone can make a low power consumption fridge... a polystyrene box will do a pretty good job of keeping things cool... but if you want a chiller that chills there is no way to avoid putting more power in... and I bet that all electric fridges perform similarly in this respect... a higher wattage fridge will just do the job more quickly

[centro]

I now have enough funds saved to buy 2 x Trojan T105 batteries. The thing is, I am having second thoughts about it.

The reason I want these batteries is to run a Weaco compressor fridge (70w) for a good length of time, plus interior lights and the water pump without worrying that I am doing a leisure battery harm by discharging it beyond the recommended amount.

It seems that Trojans are the way to go. The reason I am having second thoughts is becauseI only drive the van to work twice a week (20 mile round trip) so the alternator (90amp) wont be giving the trojan much of a top up in that period plus I dont have a driveway, so the van is parked round the corner meaning I cant put them on charge.

What im afraid of is that these batteries will be neglected and reach a premature end. I cant really afford for that to happen.

Im not sure what to do?

[trentjim]

looks like your only option may be solar then...
either that or drive a bit more... you could always volunteer for meals on wheels

E D I T - OR make the battery pack easily "pullable" so you can take it inside and put it on a cosy battery conditioning charger

[ghost123uk]

In reply to Centr's post about not having enough time to charge the trojan's. More maths for Jim to do perhaps = how about having another battery and keeping it charged up at home, then occasionally taking it out to the van with an inverter and a normal battery charger ? (or connecting this spare charged up battery to a Sterling ?)

I know it's a bit of a "lossy" system but it might work

[centro]

Would love a sterling charger! but funds wont stretch that far!

The 2 trojans will fit nicely under the back seat and will be easy to access. I suppose my only/cheapest option is to take them out when not in use and get a second Lidle charger to maintain them.

I just didnt fancy lugging 2 x 28Kg batteries through to the shed and back every week.

[centro]

On the subject of sterling chargers – how much driving would I need to do with a Sterling installed to maintain 2 x T105 trojans ?

[v-lux]

Blimey, here we go again.....

If you can afford some trojan batteries, then you could also afford a sterling unit and some normal batteries instead.

2x 6v Trojans -£300ish

Or

New leisure battery + 4step digital intelligent charger with built in zero voltage loss split charging diode Sterling unit. - £400ish

You do the math.....

If you keep a look out on ebay Sterling chargers come up now and again at very affordable prices (i paid £130 for mine - which since then i sent off to Sterling for a check up, there was nothing wrong with it but they upgraded some things to current spec and charged me nothing but the postage to get it back)

There's a recent thread somewhere started by 'California dreamin' about getting batteries real cheap from local motor places = cheap batteries.

The long and short of all this is that whatever batteries you choose to buy, they need a decent charging set up or they will fail prematurely - fact (they might last months or even years without decent charging, but they will always last longer if they are charged in decent fashion)

Any system that runs from batteries should be configured by working out the usage. Start from the end use, ie work out the consumption of all the things you want to run from the power, this will decide for you how big your battery needs to be.

FYI - i run an Engel MT45 compressor fridge, Eberspacher D2 diesel heater, Stereo, LED lighting, phone charging, Laptop (via inverter) - all of this is powered from 3x 100ah batteries charged from a Sterling Alternator to Battery charger and very occasionally a Ctek M300 mains charger when on hook up.

This system is perfectly capable of running all my electrical consumers for 5days without needing additional charge. And if it did need charging, i can turn on the engine for 15mins and then go for probably another 5 days.
I'm just sharing this as it is a real world set up that i use very regularly and can give real feedback for, i'm not saying its what suits everyone, just that it works for my needs.

[AdrianC]

all of this is powered from 3x 100ah batteries charged from a Sterling Alternator to Battery charger and very occasionally a Ctek M300 mains charger when on hook up.

This system is perfectly capable of running all my electrical consumers for 5days without needing additional charge. And if it did need charging, i can turn on the engine for 15mins and then go for probably another 5 days.

<lightly baffled>

So you've got 300Ah of battery - and it'll recharge from the alternator in 15min? OK, let's assume it's really only 50% discharged - so you're only trying to put 150Ah in.

Doesn't that mean you'd need to be running a 600A alternator, even before any charging losses?

[v-lux]

You're assuming that my battery is run flat after 5 days......

[trentjim]

ooh... thats a gotcha... but this thread seems to be for wanabee power hogs rather than frugal energy misers

Pertinent factoid of the day... lifted from the Sterling Power site

input was a 180A regulated power supply... battery was 100ah open lead.. battery was 70-75% charged
"...shows that, at 13.2V, the current was merely 1A. However, if you charge at 14.8V there was 60A of charge. An improvement of 6000%."

so i'd say that with the higher voltages offered by a sterling system the system bottleneck will be the alternator itself (90A?). rather than the battery banks ability to absorb the charge current offered... but of course its impossible to get more amps out of an alternator than its maximum... there will be significant energy losses as heat when pushing high ampage into a battery and the sterling incorporates cooling phases ( & thermal protection for the alt?) which will mean the useful input charge will be lower than the alternators theoretical max output
interesting charging graphs here
http://www.sterling-power.com/images/do ... arging.pdf

[v-lux]

Of course the Sterling unit doesnt actually give a full charge after 15mins, but it does bulk charge a big whack of it in a very short time, 15mins gives a fair bit of charge.

In all seriousness though, some simple equations for re-charge (for any system, sterling, mains charger, solar etc) are as follows.

1.5 x Battery capacity ÷ amps = charge time to full charge (roughly)

so

1.5 x 300 = 450 ÷ 100 = 4.5 (ive used 100a as an average between a 70a and 90a alternator - 70a alternator will peak at around 90a and 90a alternator will peak at around 110a)

The 4.5hr figure that this gives us is to take the 300ah battery bank from full discharge (11v) back up to full charge.

Bear in mind also that the main part of this charging will take place in the early stages (batteries suck up lots of power when they're empty) and amperage will tail off as the voltage increases (slower charging)

[v-lux]

which will mean the useful input charge will be lower than the alternators theoretical max output

Not so, Syncrosimon has the shunt and control unit/display set up running on his Sterling charger and regularly sees over 100a from his 90a alternator. (iirc the peak was something like 112a)

But heat...yes! definitely makes the alternator warm that's for sure, think Syncrosimon has seen some quite high figures for that, although interestingly he's never seen a change of more than 1ºC at the battery terminals!

Its amazing how these Sterling chargers whip up such a storm