Gell Cell Batteries

[Exmoor]

I have two 4D gell cell battries for house
I am led to believe that it is written stone that you should never exceed 14.1Volts charge, I have an old freedom inverter charger which has no setting for gel cell
So is there any way I can control the charge voltage to the battries from the charger? by some sort of voltage regulator,
By the way I am no electrical expert so any answers need to be in lay mans terms
Many thanks

[noelex 77]

Gel batteries do vary in the maximimum permitted boost voltage.14.1 is low, but if want to keep it to this as simply as possible the easiest way is to install a diode in series with the battery caharger and see what the voltage is, it's likely to be close, but if is still too high you can add more diodes. Each diode will reduce the voltage about 0.6v.
The diode needs to able to accept the full current from the battery charger and the maximimum voltage needs to be greater than 12v.
So for example with a 30a 12v battery charger, any diode that exceeds these requirements will be OK.
A 50v 50a diode would be fine and gives some margin for voltage spikes.

[Rick]

One cannot install a diode between a Freedom inverter/charger and a battery bank for use with that unit.

Nothing is written in stone regarding a voltage limit on any lead-acid battery (including gel-cell and AGM).

There is only ONE important voltage for lead-acid batteries and that is float voltage applied for long periods of time. Prevailer, WestMarine gel, East Penn Mfg gel cell, FullRiver AGM and other high quality
AGM batteries designed for power inverter applications ALL need 13.7-13.9 V float, depending upon ambient temperature.

Absorption voltage may be as high as 16V for any nominal "12V" lead-acid battery as long as the charge current does not exceed (for long periods...a long period is a time approaching the thermal time-constant of the battery) the number of Amp-hours "missing" from being full. Adhering to this will allow safe charging. The varying numbers that you might read about regarding absorption voltage "limits" do not come from the electrochemists who designed the battery, they come from attempts to limit liability of warranties when batteries are abused by the users.

!4.1 Volts too low for recovering lost capacity in deep-discharge cyclical applications. !4.4 V @70deg. F is a MINIMUM absorption voltage for reliable capacity recovery.

[goboatingnow]

Why can't the diode be used. I see no reason why not.

With gels the key is to avoid overcharging as electrolyte loss cannot be replaced. In my view Gels are not a good battery technology for boats.

Dave

[CruisingFan]

There is no reason why a diode cannot be wired between any two points, however, in this case it would be counterproductive as the voltage is already low and each diode would drop the voltage by ~0.6 V.

[hellosailor]

Ex, can I rashly assume the charger has no voltage sense lead and simply is preset to put out 14.1v ?

Often this is in fact internally adjustable and a "radio" shop could probably do it for you. Sometimes this just requires locating and turning an internal trimpot. But not knowing what you've got...
...Yes there's a simple way. Run excess cable from the charger to the battery. If you look at your typical charging amperage and use a "too thin " cable, sometimes you can still use a cable with adequate capacity that simply adds several tenths of a volt in cable losses.
Not perfect but arguably better than no kludge at all.

[goboatingnow]

Originally Posted by hellosailor

Ex, can I rashly assume the charger has no voltage sense lead and simply is preset to put out 14.1v ?

Often this is in fact internally adjustable and a "radio" shop could probably do it for you. Sometimes this just requires locating and turning an internal trimpot. But not knowing what you've got...
...Yes there's a simple way. Run excess cable from the charger to the battery. If you look at your typical charging amperage and use a "too thin " cable, sometimes you can still use a cable with adequate capacity that simply adds several tenths of a volt in cable losses.
Not perfect but arguably better than no kludge at all.

Sorry hello sailer that's awful advice for any real voltage drop the wire would glow.

Dave

[savoir]

My gels charge at 14.3v without any dramas. There are 3 x Group 31 Geltech. I've never heard of that 14.1v etched in stone business.

[noelex 77]

Originally Posted by hellosailor

...Yes there's a simple way. Run excess cable from the charger to the battery. If you look at your typical charging amperage and use a "too thin " cable, sometimes you can still use a cable with adequate capacity that simply adds several tenths of a volt in cable losses.
Not perfect but arguably better than no kludge at all.

The problem with this is that the voltage drop is dependent on the current. As the battery becomes fully charged and accepts very little current, the voltage drop becomes very small. This means the charging voltage is essentially not
Changed, it just takes longer to reach the voltage.

[noelex 77]

Originally Posted by savoir

My gels charge at 14.3v without any dramas. There are 3 x Group 31 Geltech. I've never heard of that 14.1v etched in stone business.

It depends on the type of gel battery. Some will accept higher voltages, but others are more fussy. Get the correct charging voltages from the manufacturer, if they don't list these in great detail I always wonder if they have taken shortcuts with the manufacture of the batteries.
Have a look at the detail in Sonnenschein gel batteries web page for what sort of information should be supplied on the correct charging voltages.

[savoir]

What for ? Everything in the charger department works just fine. Besides, the manufacturer says 14.5v max so I'm happy.

[Stu Jackson]

Originally Posted by Exmoor

I have two 4D gell cell battries for house
I am led to believe that it is written stone that you should never exceed 14.1Volts charge, I have an old freedom inverter charger which has no setting for gel cell
So is there any way I can control the charge voltage to the battries from the charger? by some sort of voltage regulator,
By the way I am no electrical expert so any answers need to be in lay mans terms
Many thanks

Do you not have the remote panel?

[btrayfors]

Guys...

I think you missed it. The OP has an inverter/charger unit. Typically, these use the very heavy cables to the batteries both for inverter use during which they can draw 100-300 amps or so, depending on the size of the inverter and its load, and for charging the batteries. In other words, the current flow is two-way, not one-way.

You're NOT going to put a diode in that circuit.

Bill

[hellosailor]

Dave, you're simply not reading what I'm writing. Pretty much any battery cables have a voltage drop, maybe 0.2v maybe 0.4 volt often in a 10-20 foot round trip system.

IF the amperage loads are low enough and IF the requirement is only to drop a few more tenths of a volt, that can be done without glowing cables.

But since the OP did not post his battery bank capacity, or the inverter/charger power limit, there's no way to tell if there's a practical way to do this without numbers.

Let's assume the inverter/charger is a 40A unit, having no better rash assumptions to make. I can use 10 meters (5 meters each cable) of #2AWG cable to create a voltage drop from 14.4 volts at the charger's output, to 13.978V at the batteries.

That's a voltage drop of 2.93%, with a cable load never exceeding 40A, using cables which are normally rated to handle some 3x that much current in continous duty.

Glowing? Not hardly, Dave. Now, ten meters of #2 AWG battery cable won't be cheap unless you buy a cable spool end, and we don't know that 40A will do for this system, but it is easily done with no glowing involved.

But the point is easily, quickly, and repeatedly proven by simple math that you CAN indeed "tune" system voltages by exploiting the normal voltage drop that is in any battery cable system.

In my example, that's a drop of about 0.4 volts, and that's all you need to take the typical 14.4 volt "wet lead" system down to 14.0 for gel batteries. It's a kludge, but I said that up front.

[noelex 77]

Originally Posted by hellosailor

In my example, that's a drop of about 0.4 volts, and that's all you need to take the typical 14.4 volt "wet lead" system down to 14.0 for gel batteries. It's a kludge, but I said that up front.

I agree the heating should not be a problem, but you are calculating the voltage drop for a 40A current. When the batteries are nearing fully charged the current will be very low, the voltage drop will be very small and the batteries will be at 14.4v.