Solar/alternator battery bank charging questions

[Alby1]

Hey all

I've recently upgraded my battery bank and am trying really hard to navigate all the information about ideal charging regimes.

I've upgraded to 5 x Fullriver 120 AH AGM, plus a designated starter, wired to the alternator via a VSR. The battery bank is also connected to my solar array (older panels, only approx 400w total) via an Electro SBC-7120 Pv charge controller.

We're about to do our first passage and have two main questions:

- When running the engine for long periods, is it only left up to the alternator's internal regulator and the internal resistance of the battery bank once charged to stop the batteries from overcharging? Now i have the VSR i can't switch the circuit back to only the starter battery, so i'm confused how to regulate this. I've researched DC/DC chargers etc, but it seems silly to restrict my 160 amp charging capacity from the alternator?

- And using the PV charge controller, i've played with the settings to optimise Bulk/absorption/float charge voltages. However all i've read about ideal charging regimes for AGMs talk about minimum float times etc, and there's no way this will ever be achieved using intermittent current from a solar array. Therefore the battery state seems to always jump between Bulk, Absorb and Float.

Are these issues unavoidable in a boat setting or have I missed some really important info?

Thanks very much for any help that comes my way, we're hoping to leave in a couple of weeks and it would great to have a few less questions rattling around in my brain.

Cheers!

[belizesailor]

The VSR and regulators, if properly set up, should all just do their thing with no actions required. Fully automatic.

You have only an internal regulator on your alternator?

Properly configured regulators should prevent overcharging. As long as you've set voltage levels correctly overcharging should not be an issue. Undercharging is more likely to be an issue...AGMs really do not like PSOC operation...bring them to full SOC as frequently as possible...ideally after every discharge.

[belizesailor]

"Minimum float times"? Normally the time parameter that is most important is absorption time (ABT). Float is a charge end state that can go indefinately. ABT is unfortunately a cop out by charger/regulator manufacturers, it should be based on acceptance rate not time.

What do you mean by "jumps" between battery charge states? This should be a sequencial progression "bulk, absorption, float", maybe shifting back from float to absorption as load is applied.

[Alby1]

Thanks very much belize

Yes I assume I only have an internal regulator on the alternator, I haven't seen anything that looks like an external component. Is this something i should add?

When i say "jump" i meant change back to Absorption, and then sometimes Bulk, but I think you nailed it with the very obvious answer that yes there has likely been a load, so obviously that would take it off Float. So I guess I aim to remove all loads occasionally and leave in Float for as long as possible?

I'm not so worried about overcharging via the solar regulator (your point about undercharging is understood), more that the VSR charges the starter first, then switches to the house bats, but once the house batteries are full it's all down to the alternator's internal regulator limit the voltage?

[john61ct]

Most stock VRs do a very poor job charging deep cycle batts.

Put an ammeter on your bank and observe for yourself how well it performs over time, compared to the batt mfg specs.

Replacing with an external VR like Balmar MC-614 will give much better control.

As will a high-amp Sterling DC-DC charger, and that can also moderate all other charge sources as needed.

[Locquatious]

If your alternator is not your main charging source, ensure that the regulator in the alternator is set to control near your battery float voltage, which is probably 13.6-13.8V depending on temperature for the Full River AGMs. That ensures that the batteries are not overcharged for long periods due to motoring. Some alternators have alternative regulators that can give you lower regulation voltages. For example Delco 10si alternators come with 14.4V or 13.8V regulators. Earlier 10si alternators came with 14.8V regulators.

If your alternator is you main charging source, your internal regulator can be higher voltage, but you may also want to have an external regulator that provides three-stage-charging. Keep in mind though that if you have a lot of stop and go motoring, during which the engine is shut off when stopped, the external regulator will probably start a new ful-charge regimen every time the engine is re-started. That might add up to overcharging.

[Crusty Joker]

Unless you have reason to use an external regulator to rapid charge your engine starting battery, you may want to use things as they are for engine start. However it is possible to install rapid charging systems for a price. (I have installed manual control systems for some famous racers). The 'hidden' price is that your battery life is shortened an unknown amount but usually something like a couple of years. If you do not want to listen to a small engine charge the batteries, then also conserving fuel, you can put in custom systems that will charge at higher voltage and current, pushing electrons rapidly into the battery. They can get quite hot. This is not a safe way to do things. My systems always performed as designed and I never had complaints except for one exception when I went against my will and installed an air-cooled generator in a confined space, that rolled out to be serviced. The owner did not re-tie the heavy charging cables and caused a problem after the wired up the system (wrong) as an 18 volt instead of a 12 volt system. The system functioned pretty well for over 2 years, but a battery cable rubbed on belt and caused a short. Not fun exercise at sea. His description put me into 'emergency' and I was packed with tools ready to fly in minutes. He and the boat were fine. Use qualified experienced electrician and learn your boat. In brief (not short) battery discharge state and available voltage under load determine rate of charge. Voltage of fully charged 12 volt batteries should finish at 14.2 to not over 15.2 - 15.5 volts (rapid), under charge system. They will measure, disconnected, no load and no charge, 13.2 volts, = 2.2 X 6. Test them with a hydrometer. IF there is one of more damaged cells, they will not stop charging, and they will not come up to voltage.
Be confident. Not everything needs to be understood to distraction. If you have wind, anchor, steering, and floatation, celebrate! WTF, be glad you can eat canned food! Go back to basics and remember to use the anchor sparingly and far enough off shore to stay off hazardous shore! Move from a position of rest and return to it frequently with greater confidence. I will be coming along soon. Crusty

[belizesailor]

Originally Posted by Alby1

Thanks very much belize

Yes I assume I only have an internal regulator on the alternator, I haven't seen anything that looks like an external component. Is this something i should add?

When i say "jump" i meant change back to Absorption, and then sometimes Bulk, but I think you nailed it with the very obvious answer that yes there has likely been a load, so obviously that would take it off Float. So I guess I aim to remove all loads occasionally and leave in Float for as long as possible?

I'm not so worried about overcharging via the solar regulator (your point about undercharging is understood), more that the VSR charges the starter first, then switches to the house bats, but once the house batteries are full it's all down to the alternator's internal regulator limit the voltage?

Re alternator regulator. First, confirm what you've got so you know what you are working with. Take a look at images of common ext regulators, like Balmar/Sterling/Next Step/etc, so you know what you are looking for. A simple visual around the engine room, nearby spaces, and battery compartments may answer that question. If not, follow the field wire...its what external regulators use to control the alternator...and will ultimately end at an ext regulator if one exists.

Internal regulators are typically of the dumb variety. Really just intended to top up a start batt...not fully charge a big house bank. Typically the only thing you can adjust in them is voltage limit, if that.

Externals have more charging smarts and more configuration options. If set up properly they will do a more effective job of charging a house bank and give you more options for managing things like charge profiles, set points, temp compensation, etc.

Re float. If all is right, then when a regulator decides to go to float, the battery bank will already be at or very near full SOC. So, no real need to remove loads for charging/float purposes...though of course reducing any heavy loads will mean more juice goes into the battery.

Re overcharging. Yes, its all ultimately up to the regulator to prevent that. When your start and house are combined the regulator does not know this (unless like Next Step it controls combining), it just senses a sink for charge output and a certain resistance to accepting that charge. Once a given battery in that combined bank is full then it will accept less charging amps. One analogy is filing a bunch of connected water tanks from a common source...once one is full the available flow of fill water will just flow to other tanks. If the batteries are all of the same type, or at least compatible types, then this is all good...no overcharging/undercharging worries. However, mixing of battery types can cause issues.

[mitiempo]

Originally Posted by Alby1

Hey all

I've recently upgraded my battery bank and am trying really hard to navigate all the information about ideal charging regimes.

I've upgraded to 5 x Fullriver 120 AH AGM, plus a designated starter, wired to the alternator via a VSR. The battery bank is also connected to my solar array (older panels, only approx 400w total) via an Electro SBC-7120 Pv charge controller.

We're about to do our first passage and have two main questions:

- When running the engine for long periods, is it only left up to the alternator's internal regulator and the internal resistance of the battery bank once charged to stop the batteries from overcharging? Now i have the VSR i can't switch the circuit back to only the starter battery, so i'm confused how to regulate this. I've researched DC/DC chargers etc, but it seems silly to restrict my 160 amp charging capacity from the alternator?

- And using the PV charge controller, i've played with the settings to optimise Bulk/absorption/float charge voltages. However all i've read about ideal charging regimes for AGMs talk about minimum float times etc, and there's no way this will ever be achieved using intermittent current from a solar array. Therefore the battery state seems to always jump between Bulk, Absorb and Float.

Are these issues unavoidable in a boat setting or have I missed some really important info?

Thanks very much for any help that comes my way, we're hoping to leave in a couple of weeks and it would great to have a few less questions rattling around in my brain.

Cheers!

It is unlikely that you don't have an external regulator with a 160 amp alternator - look for it as posted earlier.

As long as the voltage is the same an internally regulated alt and an externally regulated alt will charge at the same rate. In other words the externally regulated alt will not charge faster. Externally regulated alts have many advantages - float if motoring for a long time, temp sensor options for both alt and batteries, adjustable absorption times for example.

Forget the hydrometer as posted by Crusty as you have AGM batteries,

With a VSR (ACR in North America) the charge sources should go directly to the house bank. It is always the bank that needs the most current. It also eliminates chattering. This occurs when charge sources go to the start battery first. The start battery comes up to voltage and the VSR combines. Because the house bank is in need of a lot of current and its size the voltage drops in the start battery. This causes the VSR to open - it will close again when the start battery voltage rises to the set point - typically 13 volts - then the process starts all over again. With charge sources going directly to the house bank this will not happen. Blue Seas has a warning on their web site about this. On a small boat with one house and one start battery it is not an issue.

As far as over charging as long as the voltages are correct this cannot happen - the batteries acceptance and internal resistance takes care of this as the batteries accept less and less current. Even then you would have to be motoring for many hours for it to be an issue. It takes 6 to 8 hours to fully charge batteries as the last 15% slows due to internal battery resistance.

With 400 watts of solar the last 15% of charge should be taken care of automatically.

[Alby1]

Really interesting and helpful feedback from you all, thanks very much for the guidance. All taken on board.

FYI one thing in defence of the VSR unit being wired (and designed) to charge the start battery first. According to my electrician who hooked it up (as well as I understand it) he said chattering will only occur if the feed wires are too small.
That is, if the wires have enough capacity, the high output current from the alternator (current @ approx 14.2 V) will always flow down the wire to the house batteries (least resistance) as opposed to the house bank pulling from the starter battery (@ approx 13.2 V) and closing the circuit. According to the VSR design specs this is how they are intended to be used, so hopefully it works.
Cheers again! This is a great resource.

[john61ct]

Chattering can be prevented by delays designed into the VSR.

The alt output also does not need to go directly to House **if** the VSR and wiring are robust enough so as to pass the full current amps not act as a bottleneck.

Starter should hardly ever be depleted enough to cause a delay in the voltage coming up to close the VSR.

Most important take away here should be check yourself what amps and volts are at the House posts while driving and SoC is at 50-60%. Ideally keep a log recording 3-4 times per hour, once voltage stabilizes and amps start to fall, continue for another hour or two, or until either V drops to Float or current drops to a couple amps - ideally latter happens before former.

Note most stock VRs, voltage never drops.

Alternatively, many modern super-fuel-efficient designs, can't charge deep cycle at all without a DCDC charger.

[mitiempo]

Originally Posted by john61ct

Chattering can be prevented by delays designed into the VSR.

The alt output also does not need to go directly to House **if** the VSR and wiring are robust enough so as to pass the full current amps not act as a bottleneck.

Starter should hardly ever be depleted enough to cause a delay in the voltage coming up to close the VSR.

I disagree as does Blue Seas. With a large house bank - say 4 GC's in series/parallel - down 50% the rush of current from start to house when the ACR (VSR) closes is often more than the charging current. Almost always true with solar and often with an alternator. This opens the ACR until voltage rises in the start battery.

It is illogical to wire charge sources to the smaller bank, almost always the start battery. The house bank always needs more current and it also makes sense for the charge sources to sense this bank, not the start battery.

[Alby1]

Thanks John61ct, will do exactly that. Sounds like a fun way to annoy everyone on board.

mitiempo i have a question.

If you wire the alternator to the house bank first, and use you're engine like most do which is only for short runs while anchoring etc, then it seems to me there's a good chance you'll rarely fully charge your starter?
And that's the whole point of this system. It chargers the starter first and foremost, then isolates it, so you always can kick the engine over. I can't start the engine off the house bank from the way we have wired it (although the house AGM's all have high CCA), so this seems risky to me?

[belizesailor]

Originally Posted by Alby1

...I can't start the engine off the house bank from the way we have wired it (although the house AGM's all have high CCA), so this seems risky to me?

Its good to have a parallel switch too, easy option to wire. This will allow you to force the relay to combine the batteries so the house can boost the start when needed.

Ive used it to nurse along a dying start batt until I could get to somewhere to replace.

Also good to know your system and have a good quality set of heavy gauge jumper cables aboard...they can be used to jumper around things as necessary to work around a problem.

[mitiempo]

Originally Posted by Alby1

mitiempo i have a question.

If you wire the alternator to the house bank first, and use you're engine like most do which is only for short runs while anchoring etc, then it seems to me there's a good chance you'll rarely fully charge your starter?
And that's the whole point of this system. It chargers the starter first and foremost, then isolates it, so you always can kick the engine over. I can't start the engine off the house bank from the way we have wired it (although the house AGM's all have high CCA), so this seems risky to me?

The start battery will be charged fully often. It will take very little current to charge the start battery. When you are charging from any source the ACR will combine at 13 volts. This happens with the alt, solar (which you have), or shore side charging. The ACR, wired properly between house positive and start positive, only cares about voltage, not its source. All charge sources should go to the house bank. I have wired many boats this way without any issues. Mainesail also recommends this, as does Blue Seas.

Yes it is a good idea to wire a switch to start from the house bank if it is ever necessary. Start batteries, like all, do have a life which will end some day.