any battery experts out there

I've been trying to sort out my aux battery problem for some time now. Basically my battery wont hold a charge. I have a c-tek D250s battery charger and a solar panel connected to it but still, the voltage drops overnight as far as 8 volts with the 40ltr engel running. I have been to battery world and other places asking for advice. They all tested my battery and said its ok although I only have 60 ah left in it. Which should still be enough to run the fridge over night until morning when the c-tek starts charging again. Any help would be much appreciated
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Reply By: Sand Man (SA) - Sunday, Aug 31, 2014 at 09:55

Sunday, Aug 31, 2014 at 09:55

If your battery is dropping to 8 volts, it is cactus. 10.8 volts is dead flat and anything that low means the battery is probably badly sulphated and will not hold a charge.
When fully charged you should have a reading across the battery terminals of 12.8 volts without a charging process applied and with the vehicle alternator supplying a charge, the measurement should be around 14.2 volts.

The only real way to test the battery is to fully charge it (if possible) on a 240v charger and then have it load tested. This will determine if the battery will hold a charge, but based on your symptoms, it is beyond recovery.
You haven't said what type of auxiliary battery you have, or what Ah capacity, but you really need a deep cycle battery to maintain your fridge. The D250S dual is a good choice to maintain your battery via the alternator and with a solar panel of sufficient capacity when stationary as well. For a 40l Engel, you need a battery of at least 80Ah or bigger.

Even though you have a D250S dc-dc charger, the battery should be charged via a 240v smart charger from time to time, to ensure sufficient time for a full multi-stage charging process is applied.

How is the Ah capacity (60Ah left in it) being measured?
This intrigues me, coupled with the 8 volt measurement you are getting.


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Follow Up By: brendan l4 - Sunday, Aug 31, 2014 at 10:12

Sunday, Aug 31, 2014 at 10:12
I have a 97Ah AC delco maintenance free deep cycle battery. Its the second one I have had in 14 months. I use it alot and I live in Cairns so that could be a factor in premature battery life. But surely I can get longer than 6 months out of one. Especially with the D250s.
Also when I installed the D250s I was told the temp sensor was for ambient temp readings. So I installed the D250s in the back of the wagon. I have know been told thats it to measure the temp of the battery. The cable will not reach the battery now.
Could this be a problem.
FollowupID: 822864

Follow Up By: Dennis Ellery - Sunday, Aug 31, 2014 at 10:21

Sunday, Aug 31, 2014 at 10:21
Brendan if you are only getting 6 months – there is something wrong with your charging and battery protection systems. Get a competent auto sparky to look at your set up.
FollowupID: 822867

Follow Up By: Member - Frank P (NSW) - Sunday, Aug 31, 2014 at 10:52

Sunday, Aug 31, 2014 at 10:52

In your follow-up above you said your Ctek is installed in the back of the wagon. Where is the battery? With the Ctek or under the bonnet?

The reason I ask is long, inadequate output cabling (positive and negative) from the charger to the battery can very much adversely affect its performance. What size cable have you used from Ctek to the battery? And have you used a chassis negative near the Ctek or run a negative to the battery? If the latter, what size is it?

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Follow Up By: brendan l4 - Sunday, Aug 31, 2014 at 11:04

Sunday, Aug 31, 2014 at 11:04
Yes my battery is under the bonnet. I ran +ve and -ve cable from the aux battery in 6mm sq also +ve from the startet battery in 6mm sq.the cable from the aux battery to the fridge in the back of the wagon is 4mm sq.
FollowupID: 822875

Follow Up By: Member - Frank P (NSW) - Sunday, Aug 31, 2014 at 12:46

Sunday, Aug 31, 2014 at 12:46

In a followup below you said "Maybe thats my problem. Lack of charge."

I think that is PART of the problem. Certainly if you're relying on solar.

A wire size calculator I use suggests your cabling is borderline adequate and that could be another part of the problem. At full output of the Ctek I think it would adversely affect the charging. I would prefer to see all cabling in your application at least 8 gauge (=8 AWG, = 8 B&S, = 8.36 sq mm), better still, 6.

What happens after a long drive when the Ctek has been powered by the alternator? Do you think the battery gets a good charge?

If your battery has been overdischarged (which it appears it has) and not fully charged promptly (which appears to be the case) then depending how long it has been in this state it will be at least partially sulphated. Sulphation adversely affects how a battery can handle a load, even after a full charge. It will appear charged but will have reduced capacity to run a load - ie it'll have no "guts".

Options as I see them:

1 Re-cable with heavier cable to improve charging efficiency.
2 Move the Ctek to under the bonnet to shorten the cable run. Can a Ctek live in the harsh under-bonnet environment? I don't know.
3 As Sandman suggested in his followup 822879 below, move the battery to the rear with the Ctek. Supply to the Ctek should be 8 or 6 gauge, IMO.

The added benefit of having your Ctek and battery together is you can use the Cteks battery temp probe to optimise charging, especially if the Ctek ends up under the bonnet.


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Reply By: Dennis Ellery - Sunday, Aug 31, 2014 at 09:56

Sunday, Aug 31, 2014 at 09:56
Are you sure you are measuring the voltage correctly?
If it has been rundown to 8 volts it should be stuffed.
If it is, buy a new battery and a cheap under voltage relay to drop the load off at about 11.5 volts protecting the battery.
AnswerID: 538428

Reply By: Rangiephil - Sunday, Aug 31, 2014 at 10:00

Sunday, Aug 31, 2014 at 10:00
I don't fancy myself as an expert , but you can do some checks yourself .

Firstly how big is the solar panel.? If it is say 150watts you will only get a max of say 7amps over about 4 hours in winter. =28 amps with maybe 3 for another 2 hours=6 on a clear day. Total say 34 amps.
If the panel is dusty and not oriented towards the sun it will be less.

An Engel 40 litre will use about 1.5 to 2 amps per hour over 24 hours that is 36 to 48 amps.

Maybe you can check the voltage at 4PM and if it is much under 12.7 then you are not getting enough charge to maintain the fridge. Although a C-tek 250s can charge a maximum of 20 amps , it can only charge how much the panel charges.

You can buy a small meter from ABR Sidewinder which will readout the cumulative amps from your solar panel during the day along with instantaneous voltage.

You will have a much better idea of what needs to be done if you do the above checks, as asking your question as it is will just elicit guesses.

Regards Philip A

AnswerID: 538429

Follow Up By: brendan l4 - Sunday, Aug 31, 2014 at 10:23

Sunday, Aug 31, 2014 at 10:23
I was told the D250s would charge the battery with 20 amps not matter what current the solar panel was producing, and all it needed was a 12 volt supply to start charging. Maybe thats my problem. Lack of charge.

Although, its been sitting at home charging in the sun for about 3 weeks with no load connected. I turned the fridge on yesterday afternoon for the first time in 3 weeks yet when I woke up this morning the fridge was 10 degrees and my battery monitor was reading 8.6 volts. I then tested with my multimeter and the same result 8.6 volts.
FollowupID: 822868

Follow Up By: Member - Frank P (NSW) - Sunday, Aug 31, 2014 at 11:12

Sunday, Aug 31, 2014 at 11:12
Brendan, if it gets a 12V supply from the vehicle alternator, then yes, it should output 20 amps to the aux battery.

But as Rangiephil said, on solar it can only output what the solar supplies, minus losses which are commonly 30%.

So a nominal 150 watt panel may deliver to the battery, via your Ctek, 105 watts, about 9.5 amps at a flat battery voltage of 11V. And you'll only get that in perfect conditions.

Rangiephil's allowances for winter sun, short days, dusty panels etc are appropriate.

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Follow Up By: Ozhumvee - Sunday, Aug 31, 2014 at 11:18

Sunday, Aug 31, 2014 at 11:18
The D250 will not supply 20 amps unless the source it is connected to can supply that plus extra required to alleviate losses..
For a solar panel to supply 20 amps for more than a few hours per day it would need to be at least 5-600 watt and even larger to supply that current outside peak sun hours.
You really should work backwards and work out what the fridge uses per 24 hours. As an example say 5 amps at 50% duty cycle at ambient of 25C equals 5 amps for 12 hours equals 60 amp hours per day.
If the weather is warmer than 25 C (which it would be in your location) then even more power is required.
FollowupID: 822878

Follow Up By: Sand Man (SA) - Sunday, Aug 31, 2014 at 11:21

Sunday, Aug 31, 2014 at 11:21

Something is running down your battery.
Do you have other devices connected to it besides the fridge?
Is the battery in the back of your vehicle, or under the bonnet in the engine compartment.

If the latter, I would strongly suggest you place the auxiliary battery in the back, close to where the Ctek and Fridge are. This battery should be of AGM design which is much safer in the back of your vehicle. It can be contained in a battery box with a 12 volt socket to connect the fridge to. Just ensure the charging cable from the primary battery to the Ctek in the rear, is of sufficient diameter. The Ctek has a built-in isolator to protect the starting battery.

Also, one other important bit of protection you need, is a low voltage cutout device, (battery protector) between the battery output and your fridge.
The Engels are a great fridge but do not have a built-in low voltage cutout and when on, will keep sucking power from the battery, regardless of its current state of charge.

A Battery Protector can be purchased for as little as $25 for an inline one, or $80 for a larger one.
Projecta produce one and is another good source.
These devices will disconnect the power drain from the battery if the voltage falls below about 11.6 volts. This level is about 1/3 of the remaining battery voltage and is as low as you should go to protect the battery for over discharge and permanent damage, similar to what I suspect you have at present.

Battery Protector


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FollowupID: 822879

Follow Up By: Darryl E - Sunday, Aug 31, 2014 at 20:25

Sunday, Aug 31, 2014 at 20:25
I am with Bill on this one.

I would think without cutoff protection you have overdischarged your battery- do it once or twice and you you effectively shorten the battery's life. as Peter calculates, it would be quite possible for the fridge to use more than the recommended(50 or 60%) threshold within a day. Full charge may help it recover, but unlikely.
FollowupID: 822907

Follow Up By: Honky - Sunday, Aug 31, 2014 at 21:07

Sunday, Aug 31, 2014 at 21:07
When charging from the alternator bypass the Ctec as it reduces the charge down to 20 amps at its best specially if you are not driving far.
In this situation you should get up to 75% of your alternator output subject to losses including wire thickness etc.
This will put in around 3 times the ctec capacity.

After doing this check battery.

FollowupID: 822908

Follow Up By: brendan l4 - Sunday, Aug 31, 2014 at 21:10

Sunday, Aug 31, 2014 at 21:10
Ok. Yeah I see your point and its a good one but how would you suggest to do this though without tools.
FollowupID: 822910

Follow Up By: Honky - Sunday, Aug 31, 2014 at 21:13

Sunday, Aug 31, 2014 at 21:13
"Engel 40 litre will use about 1.5 to 2 amps per hour over 24 hours that is 36 to 48 amps".

I would nearly double that for Darwin.

FollowupID: 822911

Follow Up By: Honky - Sunday, Aug 31, 2014 at 21:14

Sunday, Aug 31, 2014 at 21:14
Sorry, Cairns
FollowupID: 822912

Follow Up By: Honky - Sunday, Aug 31, 2014 at 21:17

Sunday, Aug 31, 2014 at 21:17
when I did my set up I had anderson plugs everywhere.
It was just a matter of unplugging the anderson plug to the Ctek and plugging it into the anderson plug on the battery box.

FollowupID: 822913

Follow Up By: brendan l4 - Sunday, Aug 31, 2014 at 21:24

Sunday, Aug 31, 2014 at 21:24
Good idea but what I dont get is. Whats the point of dc-dc chargers except for solar charge. If you get my drift, why spend good money on good gear if your planning on by-passing it. Are dc-dc chargers really worth it. You might as well go buy a cheap solar controller from jay car to do that job rather than an expensive c-tek or redarc system.
FollowupID: 822916

Follow Up By: Honky - Sunday, Aug 31, 2014 at 21:46

Sunday, Aug 31, 2014 at 21:46
I learnt the hard way on a trip to NT.
If i was to do it again I would go the smart pass which will do up to 80 amps along with larger solar panels. I only had a 120 watt
By the way, the Ctec does three things
- Increases voltage - good if the wiring is a bit thin.
- Solar MPPT controller
- Dual battery isolator

FollowupID: 822917

Follow Up By: Ozhumvee - Sunday, Aug 31, 2014 at 22:04

Sunday, Aug 31, 2014 at 22:04
The other thing to remember with the combined charger/controllers is that they will only allow charging from one source at a time, so if travelling the vehicle alternator is supplying the charge and the solar is doing nothing. The same applies if connected to mains, the solar again is doing nothing.
The solar will only be utilised when no other power source is connected which to me is a bit silly as we live in one of the sunniest places on earth, once the solar is there and paid for it seems silly not to use it all the time, especially when travelling, reducing alternator and engine load.
FollowupID: 822918

Reply By: Member - Jim B8 - Monday, Sep 01, 2014 at 07:08

Monday, Sep 01, 2014 at 07:08
I have a very similar setup, I have a Landcruiser ute as well as the Iveco. Aux battery, Ctek 250D, and a 135 watt solar panel, 80 litre fridge.
Ctek's are definitely sus in the heat, I had mine under the bonnet, in Karratha - very hot. It used to error on a hot day, I moved it to in the back (roof and canvas sides). So the aux battery, the Ctek, and the fridge is all in the back. It now works as endless power when camping, I cant flatten it.

Ctek is a pretty intelligent device, on the solar side, and it needs wiring correctly. Have you removed the solar regulator from the panel? Ctek has a MPPT regulator internally, so it cant be fed from a panel that is already regulated. You will lose a lot of charge potential if the incoming solar voltage is 12.8 volts, rather than 17 volt. Ctek steps down the 17 volts on the solar side, to a good charge voltage, and steps up the incoming from the alternator side, again, to a good charge voltage.

I have had this system in place for several years now, and have never had a charge issue.
I would-
check and see if the panel regulator has been removed
Locate the battery, the ctek in the rear, not under the bonnet, too hot
Upgrade all wiring to 6mm or more (fit fuses as per Ctek wiring diagram)
Replace battery

I believe that charge failures kills batteries early. People are fixated with installing the latest, greatest batteries, but the problem is a lack of charge. I can verify, that solar does absolutely nothing in a shed. Any good system needs the alternator, solar, and a 240 volt charger for when you are at home. Flatten a battery (even once) to 8 volts, and I would reckon that it has been damaged. If you don't use the rig every day, plug it into the 240 charger. Charging has to be constant, not a once -every - now - and - again thing
You have everything sized well, mine is even smaller on the solar. I wouldn't bother upsizing anything of the major components. My panel is 135 watts, and the fridge is an 80 lt National Luna. I live just South of Cairns now.
good luck
AnswerID: 538448

Reply By: The Bantam - Monday, Sep 01, 2014 at 09:32

Monday, Sep 01, 2014 at 09:32
I think there have been a lot of issues addressed, but THE most important thing to understand is...there is no free lunch.

These DC to DC chargers are so often being sold as mirricle devices...they are nothing of the sort.

With corrent installation and reasonable expectations they are great things......but they won't make something from nuthin and they are not always the fastest or best way of charging a battery.
In fact in may situations they are many times slower than direct connection via a dumb relay to the alternator.

The other matter is that batteries take a finite time to charge regardless of the charger being used......a good 20 amp charger may start off puting in a good solid 20 amps....but after a fairly short time the current will drop and in the latter part of the charge cycle it may be putting in 5 amps or less.

So a half discharged 80 amp battery in reasonable condition will take at least 4 hours under favorable conditions to get to a fair state of charge.

There are arguments about getting fully charged and what actually constitutes "fully charged"

But before you even get that far you need to be putting in enough to replace what you have taken out pluss losses.

If you have a deeply discharged battery, particularly one with some age or abuse to may take 6, 8 or much more hours to return to a reasonable state of charge...regardless of the capacity of the charger.

If you fail to return at least as much as you draw pluss losses, your battery is on a slippery slope and will get progressivly deeper and deeper discharged till it fails.
This syndrom is all to common in travelers.

Now this fridge.
If you are running an need an undervoltage cut out...realy everybody needs an under voltage cut out......lots of batteries would be saved.

Oh and what temperature are you running this fridge at.

pluss 2C is considered reasonable for "fridge temperatures" if you are running it lower than that at " freezer temperatures", the power consumption will skyrocket.....if set at reasonale safe freezer temp of -15C, the motor will run pretty well continuously even in a coolish place.

If this fridge is in the north and in a closed vehicle...even at +2C..the motor may run continuousy.

People are very optomistic about fridge current demand....believe nothing other than maximum continuous current draw....or what you read from your own instruments.

It will be quite easy to argue that both the battery and solar panel capacity are marginal to say the least to keep up with what you are better have it all running properly or it wont keep up.

Now this underbonnet thing.
The worst place for batteries in under the bonnet of a vehicle...some of us have no choice.
BUT it must be understood that battery life and performance is progressivly reduced above 25C.

If you have a battery charging system with temperature compensation..the sensor needs to be mounted on or near the battery.

In particular, many of the advantages of DC to DC chargers are lost if they are not mounted close to the battery

you may well be best served replacing the DC t DC charger with a simple voltage sensitive relay and plugging in the solar pannel with its inbuilt regulator when you stop.

On the matter of this solar pannel........there has to be only ONE solar regulator in the sure that there is not one on the pannel and another being the ctec.

AnswerID: 538456

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