Charging 3 battery banks with shore, engine, wind and solar

[sailinglegend]

Originally Posted by Andina Marie

....If they are in parallel they are both at the SAME VOLTAGE. How could the engine battery be overcharged without the house bank also being overcharged?.......

Most manufacturers of split charging devices dismiss overcharging as a problem because batteries determine their own charge current. Correct, but “overcharging” is not providing more current or voltage than they want. When fully charged the current will be down to nearly zero. but holding that voltage for too long will cause excessive gassing.

During the absorption phase of charging the batteries are sitting at their gassing voltage of 14.4 volts for 4 hours or more with no problems, there can be a very small amounts of gassing but the electrical energy from the current is charging the batteries. It is only when the batteries are fully charged, and still sitting at the gassing voltage, that this voltage will causes the batteries to gas heavily. By reducing the charge voltage from 14.4v to a float of 13.8v or less gassing will stop. It is worth noting that gassing voltage are based on battery temperature, 14.4v of 25C, 13.98v at 40ºC.

This has little long term affect of flooded batteries which can be topped up, but we should accept that battery gassing can be a problem for sealed batteries and we should do all we can to protect them. Gassing is good for batteries to mix the electrolyte, but not excessive gassing.

Having long absorption times with a very large service bank will cause a small starter battery to sit fully charged and gas for much too long.

Originally Posted by Andina Marie

.....by the time battery A reaches the 14.3 threshhold, charging current is down to about 10%............ At this stage the charger switches to the next stage and lowers the current......

I need to correct another mis-understanding in this other post of yours. By the time the battery reaches the 14.3 "Boost" voltage the current is at its maximum, not at 10%. The charger stays at this voltage and switches from providing a constant current to a constant voltage. This is the absorption phase and it is the battery that reduces the current, not the regulator.

[Andina Marie]

If the starting battery is fully charged the amount of current it draws when combined is negligible and so long as it stays below the gassing voltage (around 14.2 to 14.5) the minimal incoming current will do no harm.

It is frequently thought that if you have a charging source putting out 50 amps that 25 amps will go to each battery and overcharge the smaller one. But in fact this does not happen. If you have a 200 amp-hour battery and parallel it with a small lawn mower battery, the small battery has a much higher internal resistance so the current will divide proportionally with nearly all the current going to the big bank and a trickle going to the small one.

We've been making Combiners now for 20 years, all on unconditional warranty and so far have not seen the problem you recite.

[sailinglegend]

Originally Posted by Andina Marie

If the starting battery is fully charged the amount of current it draws when combined is negligible and so long as it stays below the gassing voltage (around 14.2 to 14.5) the minimal incoming current will do no harm......

But surely that is exactly the problem. The current to the full second bank maybe zero, but it's the voltage that is doing the harm. This is basic, sorry advanced, battery chemistry which can be found via Google. In absorption mode all the batteries are going to be at the gassing voltage. (They like to gas a little bit). The second bank could be very expensive Bowthruster batteries not a cheap starter battery. Some clever battery combiner/followers, like Balmar DuoCharge, can have a boost voltage input of say 14.6 volts - well above battery gassing, but the output voltage to the second bank can be set to 14.1 volts which is below the gassing voltage. This setting can automatically be reduced further by a battery temperature sensor. Balmar's regulators are even more clever. For AGMs they set the Boost voltage to 14.38, hold that for a while and then reduce it below the gassing voltage to 14.18, for the duration of the absorption stage. They then drop to an even lower Float Voltage. Why do they do this? To stop the batteries gassing too much.

I've just quizzed Balmar on these gassing issues and had some very helpful feedback which confirms exactly what I have said above. They also gave me the following feedback:

"The ability to reduce the charging voltage to the standard flooded battery by half a volt has resulted in far fewer failures on the starting battery side as a result. I've heard that from the folks at Hinckley and Island Packet in regard to substantial reductions in warranty claims for starting batteries after they began to install Duo Charges instead of battery isolators in the early to mid 2000's." - BALMAR

[Andina Marie]

Originally Posted by sailinglegend

<SNIP>
I need to correct another mis-understanding in this other post of yours. By the time the battery reaches the 14.3 "Boost" voltage the current is at its maximum, not at 10%. The charger stays at this voltage and switches from providing a constant current to a constant voltage. This is the absorption phase and it is the battery that reduces the current, not the regulator.

No, sorry.
Maximum current will occur when first charging a LOW battery, when its internal voltage is considerably below 14.3. As the charge progresses battery voltage rises. With a rise in voltage the differential voltage to the charger decreases and the current DECREASES. The current drawn by the battery KEEPS the charger output low(er) because chargers are a CURRENT source, not a voltage source.

When the voltage reaches the first threshhold current will be the lowest it has been since charging started, NOt MAXIMUM. Ask anyone who has whatched the ammeter on a battery charging, by the time it gets to 14.3 volts it is a dribble. It tapers OFF as battery voltage rises.

[Andina Marie]

Originally Posted by sailinglegend

But surely that is exactly the problem. The current to the full second bank maybe zero, but it's the voltage that is doing the harm. This is basic, sorry advanced, battery chemistry which can be found via Google. In absorption mode all the batteries are going to be at the gassing voltage. (They like to gas a little bit). The second bank could be very expensive Bowthruster batteries not a cheap starter battery. Some clever battery combiner/followers, like Balmar DuoCharge, can have a boost voltage input of say 14.6 volts - well above battery gassing, but the output voltage to the second bank can be set to 14.1 volts which is below the gassing voltage. This setting can automatically be reduced further by a battery temperature sensor. Balmar's regulators are even more clever. For AGMs they set the Boost voltage to 14.38, hold that for a while and then reduce it below the gassing voltage to 14.18, for the duration of the absorption stage. They then drop to an even lower Float Voltage. Why do they do this? To stop the batteries gassing too much.

I've just quizzed Balmar on these gassing issues and had some very helpful feedback which confirms exactly what I have said above. They also gave me the following feedback:

"The ability to reduce the charging voltage to the standard flooded battery by half a volt has resulted in far fewer failures on the starting battery side as a result. I've heard that from the folks at Hinckley and Island Packet in regard to substantial reductions in warranty claims for starting batteries after they began to install Duo Charges instead of battery isolators in the early to mid 2000's." - BALMAR

But the voltage on the starting battey will not be sitting at the threshhold voltage for 4 hours. The Combiner turns on at 13 volts so the voltage on the starting battery will be 13, not 14 +. The starting battery will then follow the same voltage curve as the house battery which will drop as soon as it reaches the gassing voltage.

Originally Posted by sailinglegend

Some clever battery combiner/followers, like Balmar DuoCharge, can have a boost voltage input of say 14.6 volts - well above battery gassing, but the output voltage to the second bank can be set to 14.1 volts which is below the gassing voltage.

My understanding of the DuoCharge was they only reduce voltage, they CANNOT increase voltage to 14.6. They are a smart Combiner with a voltage limit. However if it is a concern, and your house battery is spending significant time above 14.2 volts, our Combiners DO have this "Clever" voltage limit feature so you can turn it on and limit the voltage transferred to 14.2. We invented that in 1994 and others have copied. The Balmar can put out only about 10 amps extending charging time, our smallest Combiner can handle the output of a 100 amp alternator cutting charge time significantly. DuoCharge $250 Combiner100 $60.

[sailinglegend]

Originally Posted by Andina Marie

...The starting battery will then follow the same voltage curve as the house battery which will drop as soon as it reaches the gassing voltage.

Wrong. It may take 1 hour to get to the gassing voltage and then sit there for 4 Hours. My Victron charger works like this. I can extend the absorption time to 8 hours for my large bank.

Originally Posted by Andina Marie

The Balmar can put out only about 10 amps extending charging time...

The Balmar can handle 30 amps - with and external relay it can handle any current. My contact told me to watch out for some new innovations for the Balmar DuoCharge.

[sailinglegend]

Originally Posted by Andina Marie

... Ask anyone who has watched the ammeter on a battery charging, by the time it gets to 14.3 volts it is a dribble. It tapers OFF as battery voltage rises.

Sorry I missed this as you threw two posts at me at the same time.

Your post is dribble so this is my last exchange with you.

For those really who want to understand see the graph for a simplification of what is happening:

t is the "Boost" stage - the charger is working as a constant current source.
4t is the "Absorption phase" - the charger is working as a constant voltage source for 4 times (t) the "Boost" time. Then it the drops down to a "Float" voltage and the current drops even more than during the Boost stage.

[Forever Freedom]

I have only just seen these posts and they make very difficult reading. Unless I am mistaken, in response to a question about multi-bank battery charging, Sailing Legend offered a solution based upon generic multi-stage-smart-charge-controlled battery charging and Andina Marie seems to be pushing a product with which she has a commercial involvement. I apologize if I have misread the discussion, but I am dubious about information proffered from those with a commercial involvement , which is couched in such terms as could lead directly to a sale of their product. http://www.cruisersforum.com/images/smilies/flowers.gif

[hellosailor]

Dubious can be a good thing, but if you check around you'll see that Andina is quite open about being a vendor. The Yandina (aka West Marine) battery combiners have been on the market for decades, and long before any similar product existed. They've got a sterling reputation.

[nmit5903]

I am looking at a solution for a similar situation with three banks, house, engine and genset with two alternators, one high output for the housebank and one for the engine/starter, solar and wind.

Question on one of the earlier bits of advice:

"Echo chargers and duo chargers are not needed, the sorce voltages are already regulated and all they do is limit the current available".

What do yoiu mean that the source voltages are already regulated please?

The house bank is currently manually switched between the house and starter banks.

I have am planning to hook up the solar regulator to the house bank and now based on what I am reading, put in a Combiner100 between the house bank and the engine bank so that they both remain in good shape when I am not able to get to the boat for weeks at a time. Is there any danger that one bank or other could overcharge using a Combiner?

[Andina Marie]

Originally Posted by ebaugh

I think you are the person who originally designed the first automated battery combiner...so you are certainly qualified to answer this question.

Let's use this example, but make the house bank 1000Ah to emphasize my point. Assume the engine battery is fully charged and the house bank is down 20-30%. The sun starts shining and my solar controller is properly programmed for several hours of absorption charge since the charge rate is especially slow. And we soon see the proper 14.4V absorption for quite some length of time. Won't that potentially boil the engine start battery since it's already fully charged?

No, you can only "boil" a battery by forcing charge into it so the voltage rises too high. But since the battery is already charged you won't be able to force current into it. There is no way current will flow "up hill" and end up with a higher voltage than the incoming source.

What will happen is the starting battery, fully charged, will be sitting at about 12.8 volts. When the house bank gets up to 13.0 volts and the Combiner starts to share the charge with the starting battery, there is only 0.2 volts available for the starting battery so it will come up to 13 volts and no higher. From then on it will be at the SAME voltage as the house bank and absorbing negligible current.

In order to "boil" the starting battery you would have to also "boil" the house battery since they are both at the same voltage and controlled by the charging source regulator to safe levels.

[sailinglegend]

Originally Posted by Andina Marie

No, you can only "boil" a battery by forcing charge into it so the voltage rises too high......

Most manufacturers of split charging devices deny overcharging is a problem because, as they rightly argue, batteries determine their own charge current. “Overcharging” is not providing more current than they want, when fully charged the current may be down to zero, but holding the charging voltage for too long at or above the gassing voltage.

During the absorption phase of charging the batteries can sit at their gassing voltage of 14.4 volts for 4 hours or more with no problems, there can be a very small amounts of gassing but the electrical energy from the current is charging the batteries. It is only when the batteries are fully charged, and still sitting at the gassing voltage, that this voltage will causes the batteries to gas more heavily. By reducing the charge voltage from 14.4v to a float of 13.8v or less gassing will stop. It is worth noting that gassing voltage are based on battery temperature, 14.4v of 25C, 13.98v at 40ºC.

This may have little long term affect of flooded batteries which can be topped up, but we should accept that battery gassing can be a problem for sealed batteries and we should do all we can to protect them from gassing. Gassing is good for batteries to mix the electrolyte, but not excessive gassing.

[Therapy]

I have learned a lot here.

Setting up a system (if I ever get another boat with "systems") is going to be harder than I thought.

Harder than picking an anchor for sure.

[belizesailor]

Good post by Miane Sail on AGMs.

Im on year 9 (yep "9") for my gel house bank (450Ah) and it is still performing well.

Hopefully by the time they die the dust will have settled on the "new" battery technology debate.

For reference my regulator is a Next Step 2, twin 65A alternators directly (fused of course) to house bank, paralleling solenoids for start batts controlled by regulator.

A handy feature of this regulator is that it will hold the parallel signal high as long as house bank is over 13v...even if the alternators are not operating. So in effect it serves as paralleling control for shore and solar charge sources too. Handy when leaving the boat unattended.