Waeco Fridge Draw on Battery

Submitted: Wednesday, Feb 22, 2006 at 18:11
ThreadID: 31045 Views:12054 Replies:8 FollowUps:24
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I am looking at upgading the factory issue battery in my Nissan 4WD to a deep cycle battery (120 amp hours) with cranking capability. With this, I then intend to run my Waeco compressor fridge, with the aim of getting more hours of operation on the fridge (when the vehicle is not running) than I would with a standard battery. Experience with the standard battery is that I get 6-8 hours of operation only, and I am hoping that the upgrade may give me significantly more.

I have to set the cut out switch on the fridge to 11 volts, which will cause the fridge to automatically shut down when the battery reaches 11 volts (I need at least this voltage to be able to start the car). So the question I have is as follows.....

The fridge draws 1 amp per hour, so if I set the cut out on the fridge at 11 volts, how many hours of operation am I likely to get from the fridge before it cuts out. During this period of operation, the vehicle will not be running and therefore the battery will be receiving no to up charge.
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Reply By: waynejethro - Wednesday, Feb 22, 2006 at 19:06

Wednesday, Feb 22, 2006 at 19:06
Hey Graeme, There is no quick answer to you question for it depends on the operating envioroment of the fridge and also the size of the waeco you have and what else is drawing from your battery (interior lights radio etc. 1 amp draw sounds a bit low, not sure where you got that from. For example I have a 80 litre Waeco in my nissan and i run it on a second battery, One of the quick recovery Optuim range (around $350 to but) i think it is rated around the same amp hours. I have contacted Weaco and they have given me how many amps that are drawn in eaxh mode while the compressor is running. The average amps drawn over (actual usage) will depend on how many times the compressor cuts in to maintain required temp. I can get anything from 24 hours to 3 days depnding on these types of variances, tehn off course there is voltage drops in wiring and how often the fridger is opened and if you put warm beer into the fridge, very involved. Not sure what toen you are in but if you are Melb. try talking to some one like Phirrana In Bayswater, they are very informative. There are a lot of people out there even in the trade that have no idea what thye are talking about. Hope that helps.
AnswerID: 156527

Reply By: Derek from Affordable Batteries & Radiators - Wednesday, Feb 22, 2006 at 21:06

Wednesday, Feb 22, 2006 at 21:06
Hi Graeme

AGM is the way to go. I sell AGM's and use the 6FM90 in my cruiser. It is rated at 90 amp hours and runs my Waeco CF80 for almost 2 days depending on the weather. I must add that I use window socks on my rear windows to keep the internal temp down in the car.

I would say you are only getting 8 hours either because the battery is in poor condition or there is a big voltage drop between the battery and the fridge.

Make sure your wiring is good and thick and solder everything. Only fit a fuse at the fridge end as a fuse up front also causes voltage drop. I have never liked lighter sockets. Cut it off and fit Anderson plugs.

Your standard 4wd Battery should be 80 amps and should run a Waeco for at least 24 hours. 8 hours sounds like there is a big problem with the wiring or battery.

Regards Derek.
AnswerID: 156556

Follow Up By: MartyB - Wednesday, Feb 22, 2006 at 22:11

Wednesday, Feb 22, 2006 at 22:11
Hi Derek,
Part of your reply has confused me.
"Only fit a fuse at the fridge end as a fuse up front also causes voltage drop."
Are you suggesting running an unfused wire from the battery to the back of the car?
from Marty.
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FollowupID: 410644

Follow Up By: Derek from Affordable Batteries & Radiators - Wednesday, Feb 22, 2006 at 22:17

Wednesday, Feb 22, 2006 at 22:17
As crazy as it sounds yes. As long as it is thick and heavy wire as I sugested and insulated. Just like the unfused wire from your battery to your starter motor.

No Voltage Drop.

Regards Derek.
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FollowupID: 410645

Follow Up By: MartyB - Wednesday, Feb 22, 2006 at 22:20

Wednesday, Feb 22, 2006 at 22:20
Derek,
What happens if this insulation wears through?
Or the insulation is damaged in an accident?

Marty.
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FollowupID: 410646

Follow Up By: Derek from Affordable Batteries & Radiators - Wednesday, Feb 22, 2006 at 22:32

Wednesday, Feb 22, 2006 at 22:32
Why would it wear through ?

Depends who does the job I suspose but if it did wear through the same would happen if the starter cables wear through or are damaged in an accident.

What happens to your winch cables in an accident ? They are not fused and they are where most accidents occur.

We are tring to illiminate voltage drop not look for possible causes of fire. There are many other items of concern like the quick a/c regas jobs that use liquid LPG in the a/c, now thats cause for concern or the LPG gas take behind our kids seat in the back and we sit safe up front !

Voltage drop ! Use thick heavy wire, solder everything and fuse the fridge at the rear.

Just another thought just for the by and by. BMW fit the battery in the boot or under the rear seat in some models and it is unfused all the way the the fuse box in the bonnet.

Regards Derek.
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FollowupID: 410650

Follow Up By: MartyB - Wednesday, Feb 22, 2006 at 22:39

Wednesday, Feb 22, 2006 at 22:39
How come the fuse at the rear has less voltage drop than if the fuse is at the front?

from Marty.
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FollowupID: 410652

Follow Up By: Derek from Affordable Batteries & Radiators - Wednesday, Feb 22, 2006 at 22:43

Wednesday, Feb 22, 2006 at 22:43
Its like sucking a golf ball through a garden hose. The closer the ball the easier it is.

Best way I can explain it in easy terms. LoL

Think of the fuse as a bottle neck in the voltage traffic.

Regards Derek
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FollowupID: 410653

Follow Up By: MartyB - Wednesday, Feb 22, 2006 at 22:48

Wednesday, Feb 22, 2006 at 22:48
Thanks for clearing that up Derek.
And all these years I have believed V=I*R.
Good old Mr Ohm was wrong, he should have played golf instead of creating electrical laws.

from Marty.
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FollowupID: 410654

Follow Up By: Derek from Affordable Batteries & Radiators - Wednesday, Feb 22, 2006 at 23:12

Wednesday, Feb 22, 2006 at 23:12
1. Ohm's Law deals with the relationship between voltage and current in an ideal conductor. This relationship states that:

The potential difference (voltage) across an ideal conductor is proportional to the current through it.

The constant of proportionality is called the "resistance", R.

Ohm's Law is given by:

V = I R
where V is the potential difference between two points which include a resistance R. I is the current flowing through the resistance. For biological work, it is often preferable to use the conductance, g = 1/R; In this form Ohm's Law is:
I = g V
2. Material that obeys Ohm's Law is called "ohmic" or "linear" because the potential difference across it varies linearly with the current.
3. Ohm's Law can be used to solve simple circuits. A complete circuit is one which is a closed loop. It contains at least one source of voltage (thus providing an increase of potential energy), and at least one potential drop i.e., a place where potential energy decreases. The sum of the voltages around a complete circuit is zero.

4. An increase of potential energy in a circuit causes a charge to move from a lower to a higher potential (ie. voltage). Note the difference between potential energy and potential.

Because of the electrostatic force, which tries to move a positive charge from a higher to a lower potential, there must be another 'force' to move charge from a lower potential to a higher inside the battery. This so-called force is called the electromotive force, or emf. The SI unit for the emf is a volt (and thus this is not really a force, despite its name). We will use a script E, the symbol , to represent the emf.

A decrease of potential energy can occur by various means. For example, heat lost in a circuit due to some electrical resistance could be one source of energy drop.

Because energy is conserved, the potential difference across an emf must be equal to the potential difference across the rest of the circuit. That is, Ohm's Law will be satisfied: E= I R

BASICALY WE WANT AN IDEAL CONDUCTOR !

Regards Derek.
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FollowupID: 410659

Follow Up By: MartyB - Wednesday, Feb 22, 2006 at 23:19

Wednesday, Feb 22, 2006 at 23:19
Hi Derek,
We should probably appologise to Graham for highjacking his thread the way we have. Also it is past my bedtime so I'm off to bed. Perhaps we could continue this discussion tomorrow night in our own thread, it will take me a while to digest your last post anyway.

Hi Graham,
Sorry for highjacking your thread.

nite all.
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FollowupID: 410661

Follow Up By: lungfish - Wednesday, Feb 22, 2006 at 23:27

Wednesday, Feb 22, 2006 at 23:27
I concurr with Marty, circuit breakers[manual] @ both ends. BTW Kirchoff's Rule still exists? or have things changed recently?

eng
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FollowupID: 410665

Follow Up By: Derek from Affordable Batteries & Radiators - Wednesday, Feb 22, 2006 at 23:43

Wednesday, Feb 22, 2006 at 23:43
Laser point thermometer.

On a cold engine with a fridge that has run all night test the temperature of the wire, fuses, breakers (Auto or Manual) and see where the heat is. Normally the fuse up front or the thin wire supplied by some installers.
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FollowupID: 410667

Follow Up By: hl - Thursday, Feb 23, 2006 at 09:05

Thursday, Feb 23, 2006 at 09:05
This is VERY dangerous advice.
NEVER run a heavy wire to the back of the car without a fuse or fusible link near the battery!
As for a fuse having less voltage drop at the end of the line....
all I can say COMPLETE AND UTTER GARBAGE.

Cheers
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FollowupID: 410692

Follow Up By: Derek from Affordable Batteries & Radiators - Thursday, Feb 23, 2006 at 09:42

Thursday, Feb 23, 2006 at 09:42
Thank you for your technical explanation.

I'm sure BMW are going recall all their vehicles and fit a fusable link or fuse to their rear mounted batteries.

O yes and a 7 series 740i cranks at 400amps.

I would like to see the size and price of such a fuse.

Regards Derek.
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FollowupID: 410695

Follow Up By: Mainey (WA) - Thursday, Feb 23, 2006 at 12:19

Thursday, Feb 23, 2006 at 12:19
Derek,
I believe your fuse placement proposal is incorrect and also very dangerous, for the following reasons;
If you fit a fuse at the far end of the power cable, near the fridge, you then have the full length of the cable in the undesirable position that it's UNprotected, when a ‘short’ occurs, for any reason at all, and in any position with-in the length of the power cable, it will probably start a fire... :-(

If a HRC fuse is fitted to the battery (+) lug and the power cable is then inadvertently 'earthed' anywhere in its entire length the HRC fuse will blow and no damage will occur to your vehicle, power cable or the fridge, however when a fuse is fitted at the fridge end and the same 'earth' occurs, a fire is the most probable result!!

A ceramic “HRC” fuse will give a 'zero' voltage drop
size; ~35mm long
price; ~$10
They will protect the vehicle, battery & also fridge

Yes, they are really "Affordable" very effective and simple to fit.
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FollowupID: 410724

Follow Up By: Member - Phil G (SA) - Thursday, Feb 23, 2006 at 12:40

Thursday, Feb 23, 2006 at 12:40
I also don't agree with Derek's suggestion but agree that conventional fuses can be more trouble than they are worth.

IMO, for safety reasons, you must use some sort of short circuit protection. We drive these things on badly corrugated roads which easily test the wire's insulation. If you look at a BMW, Toyota or anyone else the starter morot wire is naturally unfused - its also encased with several layers of insulation, routed away from any metalwork and is held away from metalwork by specially made plastic, or insulated metal brackets. Can't tell me that anyone on this forum will go to those lengths to protect the wiring to their fridge. The problem with a short is that it will cause a fire under the bonnet, and from personal experience, I suggest that be avoided :-((

Conventional fuse holders corrode very easily and its the poor contact in the holder that causes the voltage drop.

I suggest two other alternatives. Firstly, I use fusible links, which have considerably less resistance than a fuse which is why vehicle manufacturers use them for high current circuits. Second (cheap, but workable) alternative is to solder a 40amp blade fuse into the battery end of the circuit, and cover it with insulation. By soldering the fuse, you overcome the potential resistance problem from a crappy fuse holder. But if you blow the fuse, you'll need to get the soldering iron out to fix it - but in reality it never blows unless you have a short circuit.

In fact I solder all fuses I use so they are as reliable as possible - I've had a gutful of fuse holders over the years.

Cheers
Phil
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FollowupID: 410727

Follow Up By: Mainey (WA) - Thursday, Feb 23, 2006 at 15:50

Thursday, Feb 23, 2006 at 15:50
Phil, you have given some of the same reasons I use a HRC ceramic fuse, they have the added benefit that the fuse is bolted direct to the (+) battery terminal, if one 'blows' I just unbolt it, check as to why it 'blew' in the first place and fix the fault, then replace it.

I’ve never heard of any competent auto sparky connecting the fuse at the far end of the power cable, leaving the power cable exposed to risk, away from the battery when used in the usual Aux battery and fridge scenario as used in 4WD vehicles here in Australia.
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FollowupID: 410762

Follow Up By: Mike DiD - Thursday, Feb 23, 2006 at 21:10

Thursday, Feb 23, 2006 at 21:10
The current flowing in the wire will be the same at the front as at the rear of the vehicle, therefore the voltage drop across the fuse will be the same regardless of which end you put it.

BUT, if you have a lousy fuseholder or fuse, then the higher temperatures in the engine compartment will cause it to overheat sooner.

The solution is simple - use a decent fuse and fuseholder - and put it where it provides maximum protection - at the power source.

Mike
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FollowupID: 410850

Follow Up By: Derek from Affordable Batteries & Radiators - Thursday, Feb 23, 2006 at 21:18

Thursday, Feb 23, 2006 at 21:18
... and good heavy wire.
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FollowupID: 410851

Reply By: Sand Man (SA) - Thursday, Feb 23, 2006 at 08:41

Thursday, Feb 23, 2006 at 08:41
Graeme,

Your idea of using a "dual purpose" battery will only help in prolonging the operating life of the battery.

What it will not do is protect you for accidental complete discharge of your one and only battery. If this happens mate, you will be in the s.h.i.t.

The whole purpose of a dual battery system is to ensure that you will always have a battery that will start your vehicle, no matter what. If the primary battery should somehow pack it in, any auxiliary battery can be used to temporarily replace it.
A "deep cycle" battery is designed to enable a prolonged discharge in between recharges and the best one of all is the AGM type which allows deeper discharge without permanent damage to the battery and quicker recharge to almost 100% capacity via your vehicle alternator.

Anything else Graeme is a poor compromise.
Bill


I'm diagonally parked in a parallel Universe!

Member
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AnswerID: 156603

Reply By: Member - Collyn R (WA) - Thursday, Feb 23, 2006 at 13:17

Thursday, Feb 23, 2006 at 13:17
Dereck

Ohm's Law is not relevant here: the physical location of a fuse in a circuit can have no possible effect on the overall voltage drop in that circuit. Ohm's Law merely shows the amount of that drop.

A fuse's inclusion will result in an identical drop (for that fuse) no matter where you site it in that circuit. Further, the voltage drop of a correctly-rated and correctyly installed blade fuse is too small to be concerned about.

But what one DOES need to be concerned about is the suggestion that this fuse should be located at the appliance end of the cable. This negates the very purpose of the fuse - which is to protect against high current discharge and risk of fire in the by no means improbable event of that cable shorting to earth.

There is in any case, often a fuse at the far end anyway - makers such as Engel include it in the cable connector, others within the appliance. But the purpose of THAT fuse is not to protect the cable, but simply the appliance from further damage in the event of internal failure.

Main starter and charging cables are generally not fused simply because their construction and fastenings are such that failure through breakage, abrasion etc is unlikely. They are also tucked away, where accidental damage is slight.

The risk with fridge and other similar cables is far higher.

Whilst voltage is to be avoided as far as possible, and especially with fuses, it is inadequately-sized cable that is almost always the problem.

Re fridge consumption figures. There are many variables but one often overlooked is this:

For virtually any fridge of any size/make,condition/usage - energy consumption increases by 5% for every 1 degree increase in ambient temperature. It also increases by the same amount for every 1 degree lower the set temperature.

Thus fridge consumption checked in Ballarat is may be as little as half that if measured in my home town of Broome. This tends to make generalised statements re consumption almost meaningless.
Collyn Rivers

Collyn Rivers
AnswerID: 156664

Follow Up By: lungfish - Thursday, Feb 23, 2006 at 14:27

Thursday, Feb 23, 2006 at 14:27
Collyn,

For virtually any fridge of any size/make,condition/usage - energy consumption increases by 5% for every 1 degree increase in ambient temperature. It also increases by the same amount for every 1 degree lower the set temperature.

This explains the measurements I was getting when testing my fridge!...I was getting run-current of 6A[ramping from 4.5A after the initial peak].

I presume that the 5% change is compound?[as opposed to simple?]Looking back on the figures I am not getting a linear function, can you please point me to a link for further investigation?

Thanks....eng[late Wok]
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FollowupID: 410749

Reply By: Derek from Affordable Batteries & Radiators - Thursday, Feb 23, 2006 at 15:18

Thursday, Feb 23, 2006 at 15:18
Graeme

You now have have a almost complete solution to your problem.

Like I said all along...

1) Use thick heavy wire front to back. (8 B&S)

2) If you are going to do a poor fit / insulation job then fit a 100 amp Fusable link.

3) Fit a fuse at the Fridge end to protect the circuit when or if the fridge causes a problem.

4) Use Anderson plugs if possible.

5) Enjoy cold beer.

Regards Derek.

PS: Rememeber to solder everything.

AnswerID: 156678

Follow Up By: Graeme0750 - Sunday, Feb 26, 2006 at 21:51

Sunday, Feb 26, 2006 at 21:51
Thanks Derek. Could you expand on your reference to 8 B&S Cable? Not sure wether this is figure 8 or single strand, and how thick it is.

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FollowupID: 411455

Follow Up By: Derek from Affordable Batteries & Radiators - Sunday, Feb 26, 2006 at 22:04

Sunday, Feb 26, 2006 at 22:04
8 B&S is a single core wire available in black and red.

The STD 8 B&S is 8mm2 with 93 strands of 0.32mm the insulation is 1mm thick. The outer diameter is 7mm.

Regards Derek.

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FollowupID: 411458

Reply By: Member - Collyn R (WA) - Thursday, Feb 23, 2006 at 15:55

Thursday, Feb 23, 2006 at 15:55
Lungfish
The increased draw will manifest more as an change in the on/off cycling ratio rather than steady state compressor current draw - although that may change as copper varies in electrical conductivity with temperature.

A very good reference is Ample Power's book 'Living on 12-Volt' but it's confusing because the Yanks still use imperial units (that are not even always the same as other's used to use).

There's a much simplified (and metric) version in 'Motorhome Electrics' written by someone I'm not supposed to mention here. It's in a section that outlines what's needed to build one's own fridge (incidentally, thata's a lot easier than many suspect).

Briefly, the energy required to heat or cool something depends on:

1. What it's made of (specific heat)

2. Its temperature

3. Its mass (for this purpose - that's how much it weighs).

The amount of energy actually needed is the mass of that substance (in kg) times its specific heat capacity as a percentage (water is 100%, most things you eat and drink are 70-90%) times the desired temperature change in degrees C.

As an example, the energy required to heat/cool water is roughly 1.15 watt/hours per kilogram for every degree C.

The above is the minimum theoretical amount of energy (not even a PR company can do it with less!). In practice one needs allow about 50%-60% more.

That there is an increase in the energy used to heat something by a lot rather than a little is obvious. What may not be though - is that the difference is significant.

A 60-litre Engel in Bendigo may draw (say) 30-40 Ah/day most year round. Up here (Broome) right now it will draw way over 80.

Oh yes - to answer the other bit of your question - the increase/decrease is linear.
Collyn Rivers
AnswerID: 156681

Follow Up By: Wok - Friday, Feb 24, 2006 at 08:07

Friday, Feb 24, 2006 at 08:07
Thanks Collyn,

I will look into 'M H' .

eng
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FollowupID: 410944

Follow Up By: Mike DiD - Sunday, Feb 26, 2006 at 13:08

Sunday, Feb 26, 2006 at 13:08
. . and it's important to be aware of the huge Latent Heat of Fusion/melting. It takes the same amount of energy to freeze ONE litre of water as it does to cool EIGHTY litres of water from 2 degree to 1 degree.

And vice versa for melting - that's how ice in an Esky works.

Mike
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FollowupID: 411357

Reply By: Mike DiD - Thursday, Feb 23, 2006 at 21:28

Thursday, Feb 23, 2006 at 21:28
I've stumbled across some well disguised test results for various fridges at 20 degrees and 30 degrees air temperature. However the authors realised how rare and valuable actual test results on fridges are, so the info is encoded. But I have cracked the code.
http://www.airaus.com/airaus/category.jsp?categoryID=49

Here are two examples for Waeco model numbers I recognise.

CCF-40
Temp -Run/24hr - % - watts - Amps - amphrs/24hrs - amphrs
--20---- 5.28hrs-- 22%- 45----- 3.8-------- 19.8----------- 0.8
--30---- 7.68hrs-- 32%- 45----- 3.8-------- 28.8----------- 1.2

FF-90
Temp -Run/24hr - % - watts - Amps - amphrs/24hrs - amphrs
--20---- 8.4hrs-- 35%- 65------- 5.4------- 45.5------------ 1.9
--30--- 10.8hrs-- 45%- 65------- 5.4------- 58.5------------ 2.4

It gives an indication of how much variation there is between models and as temperature varies.

Mike
AnswerID: 156759

Follow Up By: Wok - Friday, Feb 24, 2006 at 08:15

Friday, Feb 24, 2006 at 08:15
Mike,

Good work, c.f 60l Trailblaza, measured 50% @ 45c [16l water load]
This makes it easier to compare performance...if the load were standardised! Do you know what load they used?

eng
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FollowupID: 410946

Reply By: Mike DiD - Sunday, Feb 26, 2006 at 13:02

Sunday, Feb 26, 2006 at 13:02
I just found this extract of a test published by 4WDMonthly mag that gave some actual amphour consumption. Of Opening/closing and putting warm food/beer will increase the loading, so this is really a MINIMUM consumption.
http://www.waeco.com.au/news.asp?id=147

They tested in a cycle ranging from 15 to 55 degrees and for a Waeco CF40 the total consumption over 24 hours was 22.5 amphours (not amps). Even at 55 degrees the AVERAGE consumption was only 2.2 amps - or 2.2 amphours for one hour.

No wonder people have trouble understanding electrical units if authors can't be bothered checking their own text for accuracy. The measure of how much a load draws at an instant in time is Amps - the measure of how much it draws over one hour is AmpHours.

Mike
AnswerID: 157138

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