Engel MTF-60 & batteries - help please!!

[ajburnet]

Hi,

I am currently touring the UK, Ireland, possibly Europe and then onto New Zealand and Australia.

We have an Engel MTF60 Fridge / Freezer with a two zone compartment. The fridge is operating well although we are not achieving the kind of battery life the numbers would suggest so I would be really grateful for some helpful advice please!

Power: 110ah leisure battery (new, standard wet cell deep cycle battery)
Engel consumption: 2.8 amps (measured using multimeter)


After a charge on mains (the motorhome has an in-built zig x-7 battery charger / conditioner - i.e. not trickle and monitors / adjusts the voltage level) for 4 days (i.e. assuming battery is now fully charged) we get at least two evenings with the fridge / freezer on freeze (setting 4 out of 5 - it is off for approx 40% of the time). We are driving at least 3 hours a day and use a generator every other night for 4 -5 hours.

We are finding that after a few days after the first full charge the battery does not appear to be charging fully through driving and generator use, i.e. we cannot get more than one evening (if that) without depleting the battery to the point the fridge can't operate (presumably lower than 12v). This includes a day when we drove for over 10 hours!

I have checked the alternator and it is providing over 12v and the battery charger (when on generator) is also providing around 13v.

How long should we reasonably need to charge this battery fully, is this normal? If yes, what can you suggest (e.g. dual battery setup, solar panels etc..). We would like to be able to stay somewhere for at least 2 - 3 days without having to run the generator or drive ideally, certainly this will be the case in NZ and Aus.

Any help and advice would be most appreciated - thanks!

 

[UK4X4]

Fridge is comsuming the correct ammount ie amps correct

my 45 which has the same type compressor lasts 3-4 days on a standard battery

110amphr...at 50% usage gives you 55 amp hour usefull power

your engel should tick along about 1/2 the time with compressor on

so if its on for 12 hrs at 2.8 amps it consumes 33.6 amps a day

so you should be able to run it for about 1.5 days.

Sounds like your battery is not holding a charge.

or your not charging at all

 

[DaveInDenver]

Power: 110ah leisure battery (new, standard wet cell deep cycle battery)
Engel consumption: 2.8 amps (measured using multimeter)

we get at least two evenings with the fridge / freezer on freeze (setting 4 out of 5 - it is off for approx 40% of the time). We are driving at least 3 hours a day and use a generator every other night for 4 -5 hours.

What I think are relevant points.

First, calculating battery life, you are on the right track. When you say off 40% of the time, that means you are running around 24 minutes off and 36 minutes on per hour? If so, at 2.8 amps measured you are running about 1.7 A-hr and your 100 A-hr battery should be able to do a 80% discharge (so in other words, a 20% state of charge), so say it will give you as much as 70 A-hr, so it should last 42 hours approximately. Certainly a day or two should be practical with a little care to keep it out of the sun, maybe turn it up a little at night if possible.

I have checked the alternator and it is providing over 12v and the battery charger (when on generator) is also providing around 13v.

If these are your measured voltages, then this might be the problem. To charge a lead acid battery you need to raise the voltage higher than its nominal open circuit voltage. How much higher is determined by how much current and time you have or want to use and the battery's capacity.

If you have a very long time or very low current, then you don't need to be much higher voltage. Typically a minimum of about 2.25V per cell and about 1/10th the capacity are needed, so if it's a 6 cell battery (nominally 12V) at 100 A-hr, you need 13.6V or more to reverse the reaction at 10 amps for 10 hours (the C/10 rate). You can use lower current if you extend the time out, so 1/40th the current for 40 hours will require a lower voltage yet, around 12.5V or so I would guess. This is how battery maintenance systems work, a slow, low voltage trickle charge.

Typically for a faster charge (charges less than about 3 or 4 hours), as the engine-driven system would be, the required voltage and current are higher. Typically you want 2.35V to 2.45V per cell, so around 14.0V to 14.5V for the C/5 rate, which will also require 20 amps in your case.

If the charging systems are not meeting your battery's requirements (find the charge/discharge curves for your brand and model) you are charging the battery a lot less than you expect, if at all.

 

[IggyB]

Here's the current draw chart for the regular 60 - either set on fridge or freezer.

http://www.engel-usa.com/images/MT60F%20curve.gif

Amperage shown on chart takes off time into account - so it's total draw per hour of fridge use.

It sounds like the battery charger is doing it's job (given adequate time) but the alternator is not putting out enough voltage to charge a depleted battery.

What is the amp rating of the battery charger? If it allows the fridge to stay on for 2 days after 4 days of charging and only an evening or so after a few hours of charging it may be too small of a capacity.

My C-Tek is only 3.3 amps and 5 hours on generator would put back roughly 15 amps - a little more than half a day use on 1.5 setting on my 60.

One option is when you're driving, use an inverter - 12 volts to 220volts. The fridge will automatically switch to 220v and the battery will be charged faster since it does not have to power the fridge.

 

[Curmudgeon]

I have checked the alternator and it is providing over 12v and the battery charger (when on generator) is also providing around 13v.

If your alternator is providing less than about 13.2 volts, you are not fully charging your batteries. A 12 volt battery should be about 12.7 volts when fully charged and stabilized. An alternator putting out less than that can never fully charge a battery. Rather than saying "over 12v" it would be helpful if you gave us the exact voltage it is producing.

You make mention that this is a motohome, so your Engel is probably not the only thing drawing from the battery. What other loads do you have in addition to the Engel? And there are probably also some phantom loads you are unaware of.

-

 

[ajburnet]

Exact numbers...

Hi,

Many thanks for your help, much appreciated!

The battery charger (Zig x-7) is providing 13.65v at 12.5 amps (when not connected to the battery - not sure if it ramps up depending upon the state of battery charge?)

The alternator is providing 12.65v at 18amps.

The battery is a numax wet cell leisure battery (110ah).

Rgds,

Alex

 

[ajburnet]

Other motorhome loads..

Forgot to respond to the last question!

The motorhome electrical load is running off the main vehicle battery (isolation switch on control panel allows for this).

I have checked with the multimeter and the only current draw on the leisure battery is the Engel, no current draw is shown when the fridge is off.

Thanks again.

Alex.

 

[ajburnet]

One more bit of info...

Not sure if this is relevant, but the alternator charges the main vehicle battery at 13.84v - I assume the voltage drop is caused by the zig control panel / charger unit, but not sure if this is normal on an alternator charging two batteries?

Alex.

 

[ajburnet]

Thanks for the advice so far!!

Thanks for the advice so far, starting to make it a little clearer!

 

[Curmudgeon]

The alternator is providing 12.65v at 18amps.

That is not nearly enough voltage to fully charge a battery. It appears you have found the problem. Charging voltage should be at least 10% above nominal battery voltage. Now you need to locate the source of the voltage drop.

 

[proto]

Just to give you another diagnostic tool, you can estimate your battery's state-of-charge by directly measuring the voltage at the terminals (this is 'open terminal' with no current going into or coming out of the battery).

The numbers I go by:

12.65V -- 100%
12.45V -- 75%
12.25V -- 50%
12.05V -- 25%
11.90V or less -- Discharged

But you can dig up more refined charts on the web, such as this one:
Lead Acid Battery Charging

This would let you check the battery after charging to find out what it's real status is. You might find out that charging from one source nets a pretty full battery, but from another only gets you half a charge.

 

[ajburnet]

Thanks - any tips!?

Thanks for the advice. Presumably I need to test for voltage pre control panel and after and work back from there?

Is there a simple way to resolve this, i.e. by re-running cabling from the alternator or using a 12v charger to charge the leisure battery from the vehicle one? Looking for the quickest solution given we are already on the road and this is forcing us to use campsites more than we would like!

Thanks again - really appreciate your assistance.

Alex.

 

[ajburnet]

Next steps...

Thanks for the advice so far. I assume I need to compare voltage of incoming alternator cabling and see where it enters the motorhome power system to determine where the drop is?

Is there an easy way to resolve this? Can the batteries be charged together by running new cabling (presumably in series?), or is there a 12v battery charging option out there that would help (and could be used when I setup a 4x4 vehicle for the NZ / Auz leg of the trip)?

Many thanks again!

Alex

 

[ajburnet]

Still struggling!!

I've been trying to find the point of voltage drop but as yet no luck! The wiring it almost impossible to get at to take a ready between the battery and leisure battery. I have checked the charger and control panel and the cabling from the alternator does not appear to route via it. Also, the cabling looks to be in good condition and around 5mm thick, certainly more than 2.5mm thick.

One thing I have noticed is that the voltage on the leisure battery (when on the alternator, not connected to mains) does occasionally read 13.8 (i.e. same as vehicle battery) but only for a short period of time. Could there be a problem with the relays - could they need replacing?

Any other thoughts??!