Charging Multiple Battery Banks

[transmitterdan]

As always Maine Sail is exactly right.

The only thing I would add is that there are some true multi-bank chargers out there. One is made by Xantrex (XC5012 I believe). It allows different programs for each of 3 outputs. But it has a significant flaw in my view that it can only deliver current to 1 of the 3 banks at a time. So it cycles through each bank trying to find the one that is most discharged and gives more time to that bank. It destroyed my bank of 5 AGM batteries (2+2+1) by feeding 15-16V to all 3 banks in a cycling fashion while the boat was unattended. Xantrex help desk said the regulation circuit was failed but I do not believe that is true. For one thing it displayed the voltage correctly. And it would charge a fully discharged bank at lower voltage due to current limit activation. A current limit circuit cannot work unless the regulation circuits are functional. I believe there is a software bug in the microcontroller such that it became convinced the batteries should be equalized and that destroyed the AGMs.

I have since given up on multi-bank chargers for exactly the reason Main Sail notes. Nearly all of the multi-output chargers operate the same as a single charger with all batteries in parallel. If this design is destroying batteries everywhere then we would surely be able to find many examples.

[sailinglegend]

Originally Posted by Maine Sail

.....With a proper charging algorithm both banks get the same "gassing" voltages for the same amount of time.

Correct.

I've just read over my postings and there is one point I failed to mention that is the key to my argument - sorry!

During the absorption phase of charging yes 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 charging voltage is charging the batteries. It is only when the batteries are fully charged and accepting no current, but still sitting at the gassing voltage, that the electrical energy from this voltage has to go somewhere and will causes the batteries to heat up and to gas more heavily.

For excellent info on gassing see Victron's Energy Unlimited brochure @
http://www.utu.lt/linkkitiedosto.asp...id=187&sid=523

One quote:

Once charged the battery can no longer take up energy, and any
further energy added is used to decompose water into hydrogen gas and oxygen gas.

My point all along is why drive one more nail in a batteries coffin when with a litlte more care over-gassing of sealed batteries could be avoided.

[Albro359]

There is another alternative to a combiner and that's an FET isolator.
Traditional diode isolators drop 0.7V butthese newere FET isolators from Vetus and Victron only drop about 0.01V...so nothing really.
They provide an error free way of charging 2 or more banks from one alternator.

But if you already have an alternator for charging the start battery, I'd leave that in place and the big alt for charging the house bank. The genset no doubt runs a battery charger as well, what about using a small one to charge its start battery ?

Cross combining echo chargers and alternators is probably not a good idea. One charging source at a time per battery bank o'wise the regulators get confused.

[s/v Beth]

Legend, your argument only holds "water" if the battery types are different. If fact, it seems to me to be a lot of gas.
Why use different battery types? For the small amount of $$ I would save to get a fancy 12 volt, (as opposed to two 6 volt Trojans for my starter pack) I could not buy all the electronic gismos needed to make sure they all gas the same. Go with the same battery, make it all one block during charging, and disconnect when you are not. Save your $$ for amp-hours and solar panels.

[goboatingnow]

Originally Posted by Albro359

There is another alternative to a combiner and that's an FET isolator.
Traditional diode isolators drop 0.7V butthese newere FET isolators from Vetus and Victron only drop about 0.01V...so nothing really.
They provide an error free way of charging 2 or more banks from one alternator.

But if you already have an alternator for charging the start battery, I'd leave that in place and the big alt for charging the house bank. The genset no doubt runs a battery charger as well, what about using a small one to charge its start battery ?

Cross combining echo chargers and alternators is probably not a good idea. One charging source at a time per battery bank o'wise the regulators get confused.

Regulators don't get confused. See mine , Andinas and others on this subject. Your post is not good advice. Direct all available charging facilities at the bank that needs it. ,slave charge by one means or another batteries that need little charging. Don't waste alternator capacity by dedicating it to charging batteries that don't need it

Dave

[Maine Sail]

Originally Posted by goboatingnow

Regulators don't get confused. See mine , Andinas and others on this subject. Your post is not good advice. Direct all available charging facilities at the bank that needs it. ,slave charge by one means or another batteries that need little charging. Don't waste alternator capacity by dedicating it to charging batteries that don't need it

Dave

+1... I've met confused humans before but not a confused regulator...

[colemj]

Originally Posted by sailinglegend

During the absorption phase of charging yes 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 charging voltage is charging the batteries. It is only when the batteries are fully charged and accepting no current, but still sitting at the gassing voltage, that the electrical energy from this voltage has to go somewhere and will causes the batteries to heat up and to gas more heavily.

For excellent info on gassing see Victron's Energy Unlimited brochure @
http://www.utu.lt/linkkitiedosto.asp...id=187&sid=523

One quote:

Once charged the battery can no longer take up energy, and any
further energy added is used to decompose water into hydrogen gas and oxygen gas.

My point all along is why drive one more nail in a batteries coffin when with a litlte more care over-gassing of sealed batteries could be avoided.

We use a combiner. Our house batteries are Trojan 6V T105 and our start batteries are (were) beige-standard Walmart maintenance free cheapies commonly used in autos. While still FLA's, the start batteries are completely sealed with no way to add water without prying up and damaging some plastic that will not go back together.

All charging sources (alternators, solar and AC-powered) are set at bulk/absorption 14.8V, and reach that almost daily through most of the absorption time. In other words, the batteries are at 14.8V for several hours each day.

We recently replaced the starting batteries after 15 years. The house went through three sets of batteries in this time frame. When replacing them, I pried off the plastic covering the cell water holes and found that they were still full of water. So no significant water loss had occurred over the past decade and a half. I can only assume that also meant no significant gassing, although the sealed design may allow more recombination of gasses with condensation back to liquid water.

In fact, it is possible the start batteries did not even die of old age, let alone over-charging, because we took a direct lightning strike that destroyed all of the electronics and electrics on the boat - including shorting and boiling out the house bank and destroying the alternators. The start batteries died a couple of weeks after the strike, so it is possible that they were also damaged by it.

Now we have some type of inexpensive Columbian-brand sealed batteries picked up at a local store in Central America for our start batteries, and I expect they will also perform just fine for many years under the combiner.

BTW, Yandina will replace their combiners for free even when they are 15yrs old and have taken a direct lightning strike and suffered a complete meltdown. They were the sole manufacturer of equipment on our boat - new or old - that extended that offer (actually, they did not extend it - it is simply their standard policy). Balmar does not - not even on 1 day old equipment struck by lightning, let alone equipment past the warranty period.

Mark

[nmit5903]

I am convinced - where do I buy a Yandina Combiner in Australia? If the starter bank (two N70's) fails after 5 years or so due to over gassing - which sounds unlikely - but starts each time I go to the boat after a period of non use - I'll be happy. If I get 10-15 years the next owner will be happy!

Thanks all for your advice and discussion. That's the real beauty of the forum - priceless!

Will let you continue to debate whilst I try and source a combiner here in Sydney.

[gspeak]

Originally Posted by nmit5903

I am convinced - where do I buy a Yandina Combiner in Australia? If the starter bank (two N70's) fails after 5 years or so due to over gassing - which sounds unlikely - but starts each time I go to the boat after a period of non use - I'll be happy. If I get 10-15 years the next owner will be happy!

Thanks all for your advice and discussion. That's the real beauty of the forum - priceless!

Will let you continue to debate whilst I try and source a combiner here in Sydney.

M8,
As I said previously, just order directly from Yandina Marine online. If I got my order in 1.5 weeks up here in Far North Queensland, then you will definitely see yours a few days earlier than that.

If you have any questions email them before hand.


Dave
seabreeze L380 #241

[smac999]

Originally Posted by nmit5903

There are also some articles on other forums about the risk of excessive cycling with combiners:

"The primary functions of battery combiners, which include voltage sensitive relays and automatic charging relays (ACR), are:
Combine battery banks so that they can share the output of a single charging source such as an alternator or shore-power charger
Automatically isolate battery banks to prevent discharging of the Start battery bank
In some applications, as soon as a battery combiner closes to combine battery banks, it may immediately reopen because the load demand put on the charging source exceeds its output. This combining (closing) and isolating (opening) process may repeat over and over—it will cycle repetitively. When this cycling happens, the secondary battery bank may not receive a charge and can become discharged."

yes this happens with large house banks and undersized alternators. and would happen with any acr / vsr / combiner as they are all voltage based

if you have say a 800-1200ah house bank, a group 31 start, and an 80a alternator connected to the engine battery (common set up on a sail boat).

if you drained the house down to say 60%. once you start the engine, the engine battery will be 14.4v. the combiner will combine. but when you have a 1000ah battery bank at at say 11.9 volts. a group 31 at 14.4v and a tiny 80a alternator, you end up somewhere around 12.5v when all combined. so the combiner shuts off. 31 goes back to 14.4v. 30 secs later combiner turns back on. (bss acrs are set to 30 secs) and this repeats every 30 secs

it will take 2-3 times longer to charge the house as the acr cycles.

if you put the alternator onto the house battery instead. it will take hours and hours for that house bank to reach a voltage high enough to trigger the combiner. so your non deep cycle engine starting battery is draining for hours as you motor which is not good, if your lucky the combiner will kick in before the battery dies and so does the motor

with a big mismatch in battery sizes and smaller alternators the only solution is non combiner based isolator. or a freaking huge alternator that can actually hit 14v on a big discharged house bank.

[goboatingnow]

Originally Posted by smac999

yes this happens with large house banks and undersized alternators. and would happen with any acr / vsr / combiner as they are all voltage based

if you have say a 800-1200ah house bank, a group 31 start, and an 80a alternator connected to the engine battery (common set up on a sail boat).

if you drained the house down to say 60%. once you start the engine, the engine battery will be 14.4v. the combiner will combine. but when you have a 1000ah battery bank at at say 11.9 volts. a group 31 at 14.4v and a tiny 80a alternator, you end up somewhere around 12.5v when all combined. so the combiner shuts off. 31 goes back to 14.4v. 30 secs later combiner turns back on. (bss acrs are set to 30 secs) and this repeats every 30 secs

it will take 2-3 times longer to charge the house as the acr cycles.

if you put the alternator onto the house battery instead. it will take hours and hours for that house bank to reach a voltage high enough to trigger the combiner. so your non deep cycle engine starting battery is draining for hours as you motor which is not good, if your lucky the combiner will kick in before the battery dies and so does the motor

the only solution is non combiner based isolator. or a freaking huge alternator that can actually hit 14v on a big discharged house bank.

Why " so your non deep cycle engine starting battery is draining for hours as you motor" do you say that , dRaining into what.

Using a combiner always charge the bank that's used the most.

Dave

[Andina Marie]

with a big mismatch in battery sizes and smaller alternators the only solution is non combiner based isolator. or a freaking huge alternator that can actually hit 14v on a big discharged house bank.

But they do not have to reach 14 volts , only 13 volts and that happens within minutes unless you are using power from the house bank faster than the inadequate alternator can supply.

Just because the Combiner is cycling it does NOT extend charging time. At 13 volts the alternator is putting out MAXIMUM current in BULK MODE that has got to go into the batteries, (and supply the load}, it does not stop charging when the Combiner is cycling off.

If your alternator is inadequate you have to make a decision on which battery to protect so conventional installations using a Combiner favor the starting battery. The picture you paint for charging the house battery is not nearly so gloomy. Even on a severely discharged house bank it will spend the bulk of its charging time between 13 and 14 volts and the Combiner will be distributing the energy.

[sailinglegend]

Originally Posted by Andina Marie

......so conventional installations using a Combiner favor the starting battery......

All conventional cruising installers that I have ever read or spoken too - including Main Sail - recommend all your charging sources go to the Service batteries, and the Starter is only used for starting the engine.

Since only about 1% of the starter battery Ahs are used starting the engine it can be used many times without being charged and without over discharging it.

With ALL automatic systems YOU need to keep an eye on the situation so a digital Voltmeter and a digital Ammeter are essential on a cruising boat.

My American Hunter Legend has a 5 watt solar panel just to charge the starter battery. This works fine in the Med, but when my BEP VSR is in circuit it repeatedly cycles on and off. Each time it dumps 100 amps or more into the house bank. This is an extra unnecessary starter battery discharge cycle and unnecessary repeated stress on the VSR contacts. My BEP VSR combining voltage is set to 13.7v. If it was 13 volts like the Yandina the cycling in my situation would I suspect be far worse.

There is a intelligent SmartBank battery combiner that detects this problems and eliminates the cycling.

[Maine Sail]

Originally Posted by smac999

if you have say a 800-1200ah house bank, a group 31 start, and an 80a alternator connected to the engine battery (common set up on a sail boat).

Common?? An 80A alt on 800-1200Ah bank is a poorly thought out installation unless you have multiple other charge sources...

Originally Posted by smac999

if you drained the house down to say 60%. once you start the engine, the engine battery will be 14.4v. the combiner will combine. but when you have a 1000ah battery bank at at say 11.9 volts. a group 31 at 14.4v and a tiny 80a alternator, you end up somewhere around 12.5v when all combined. so the combiner shuts off. 31 goes back to 14.4v. 30 secs later combiner turns back on. (bss acrs are set to 30 secs) and this repeats every 30 secs

Again feeding the alt to the start battery on said system is just a poorly thought out system design. 60% SOC is around 12.2V and 40% SOC would be closer to 11.9V.. I would hope someone with an expensive bank like that is not regularly drawing to 40% SOC because they will have a long haul to get it back to even 80% SOC with an 80A alt...

Originally Posted by smac999

it will take 2-3 times longer to charge the house as the acr cycles.

If the system is of poor design it is still poorly designed.

Originally Posted by smac999

if you put the alternator onto the house battery instead. it will take hours and hours for that house bank to reach a voltage high enough to trigger the combiner.

Even an 80A alt on a 800Ah bank should have that bank to 13V in a reasonable time. There there will be no cycling of the relay if the sources are fed to house first..

Originally Posted by smac999

so your non deep cycle engine starting battery is draining for hours as you motor which is not good, if your lucky the combiner will kick in before the battery dies and so does the motor

Draining for hours?

Originally Posted by smac999

with a big mismatch in battery sizes and smaller alternators the only solution is non combiner based isolator. or a freaking huge alternator that can actually hit 14v on a big discharged house bank.

The proper solution is a well designed charging system. I would not consider an 80A alt on a 800-1200Ah bank with the alt fed to the start bank even close to well designed.

Combiners and Echo's and Duo's all turn on or combine at the same or very similar voltages so no advantage in the above scenario. The last choice for me would be a voltage dropping battery isolator...

It is interesting to note that The Echo Charger, Duo Charger and the BSS ACR & Yandina Combiners all turn on at identical voltages.:

Echo Charger On Voltage 13.0V
Duo Charger On voltage 13.0V
Blue Sea ACR Combine Voltage 13.0V for 90 seconds
Yandina Combiner Combine Voltage 13.0V

No matter which of these devices you put on the poorly designed system mentioned above they will all turn on/begin charging the second bank at the same voltage. Attaining 13V, even on a large bank with a small source, is not very difficult it is getting to absorption voltage that takes the time..

My point here is that a poorly designed system should not be an excuse for not using any of the above mentioned devices. They will all work properly, and as designed, if the system is also well laid out and well executed. Start with a well designed system and any of these devices will work very, very well...

[smac999]

Originally Posted by Andina Marie

But they do not have to reach 14 volts , only 13 volts and that happens within minutes unless you are using power from the house bank faster than the inadequate alternator can supply.

Just because the Combiner is cycling it does NOT extend charging time. At 13 volts the alternator is putting out MAXIMUM current in BULK MODE that has got to go into the batteries, (and supply the load}, it does not stop charging when the Combiner is cycling off.

If your alternator is inadequate you have to make a decision on which battery to protect so conventional installations using a Combiner favor the starting battery. The picture you paint for charging the house battery is not nearly so gloomy. Even on a severely discharged house bank it will spend the bulk of its charging time between 13 and 14 volts and the Combiner will be distributing the energy.

a small case ~80a alternator with external regulator at full field voltage and full bulk output will not hit 13v on a 1000ah battery bank at 50% for hours. I have witnessed it on several boats. it will sit in the mid - high 12s. and slowly make it's way up as the bank charges

with a tiny sailboat engine with a single v belt, there isn't much more you can do with the alt.

I didn't say it was a good setup. but it's a setup I've seen and delt with. and combiners simply don't work. something like the promariner proisocharge should be used.

on most boats the combiners work fine.