So.. how are you folks optimally charging your deep cell battery from the alternator?

[norman_nomad]

Ok here's the quick scoop. I have a 400 watt solar array installed on a VW Vanagon feeding an MPPT charge controller and into a 200ah battery bank. I have a Blue Seas ACR to charge both the starter battery and the solar batteries when the vehicle is running. Everything is working fine. Here are my 2 *questions*:

1) How shall I optimally charge the solar batteries from the alternator?

My immediate concern is that the voltage coming from the alternator is not high enough to fully top off the battery bank. When I drive for 30 minutes or so, the solar batteries only ever get charged to about 12.6v. These are VMax batteries and need 13v+ for full charge.

2) Is it possible/advisable to feed the alternator current directly to the MPPT charge controller and let it handle the 3 phase charge?

I haven't done this because my 4215bn charge controller maxes out at 40amps and I'm fairly certain the alternator would overload this. But is this even feasible or would it be totally ill-advised? I've done a number of searches online and haven't been able to solve this.

Any help is greatly appreciated!

[bcroe]

I am wondering if the voltage was measured while the alternator was charging, or after it was shut off (much lower)? If you are using a
diode battery isolator, you could be suffering nearly a volt drop from the alternator output. Some fixes for that could be 1. move the alt
sensing lead to the battery side of one diode; 2. set the alternator voltage a bit higher; or 3. wire a separate power rectifier bridge from
the alternator 3 phase windings to the second battery positive and eliminate a separate isolator. Bruce Roe

[joerossjr]

I asked the same thing a few weeks ago... I didn't feel like the question was well received: https://www.solarpaneltalk.com/forum...or-connection/ I decided to eventually invest in the CTEKs mentioned, since I haven't seen any other equipment that appears to do the same thing.

[Sunking]

First thing to do is check to see what Voltage your Alternator Regulator is generating. All vehicles and trucks today should be 14.2 volts. If you are using mechanical Battery Isolators you have no choice but to accept whatever the Alternator is providing.

However if you use a Electronic Battery Isolator made by Sure Power they have a Voltage Regulator built-In to control the Alternator Voltage to provide 14.4 volts for FLA and 14.2 for AGM

So the answer to your question is first make sure your Alternator Voltage Regulator is outputting 14.2 volts. Once you have that squared away there is nothing else you can do except take what you can get. The difference between 14.2 and 14.4 is not enough to make much if any difference except the length of time required. 14.4 will just be faster. FWIW 13.8 is even good, just slower.

If I had to guess your battery is deeply discharged, and your alternator just has not had enough time to bring the voltage up. Your vehicle alternator is capable of 16 volts if the Regulator will go that high. Blue Seas even sells Voltage Regulators for Marine engines to solve the problem fixed @ 14.2 volts.

14.2 is universal 12 volt battery charge voltage set by SAE for all Automotive and Marine applications. 14.2 volts is perfect for both AGM which the industry has switched to and drop in replacement LFP batteries. 14.2 was chosen because for 3 reasons.

1. Is at the Gassing Threshold Voltage. Any higher on a AGM makes it is likely to over charge, causing gas pressure to rise to high, and causing the battery to vent. Game over if that happens

2. 14.2 is perfect voltage to charge a LFP battery.

3. Also works for FLA batteries, just takes a little longer and will minimize gassing and water usage. Thing is with lead acid batteries, the lower the voltage you use, th elonger your battery last. Float at 13.6 to 13.8 is perfect, but can take 24 hours to recharge.

12.6 volts sounds like a fully charged battery not on a charger at rest.

[norman_nomad]

I asked the same thing a few weeks ago... I didn't feel like the question was well received: https://www.solarpaneltalk.com/forum...or-connection/ I decided to eventually invest in the CTEKs mentioned, since I haven't seen any other equipment that appears to do the same thing.

Thanks for the link. I read through the thread. Seems they didn't like the alternator -> MPPT idea... I'd like to better understand why this wouldn't work. My understanding is that the MPPT controller constantly tracks for optimal power...assuming the voltage meets threshold conditions (and 14v from the alternator would suffice) and amperage does not exceed the MPPT specs, the MPPT discovery algo should still work... no? It's possible (likely) I'm missing something fundamental. I do understand that the alternator puts out a constant voltage while current varies with the engine RMP ... but I'm unclear as to why this would not work with the controller ...

The CTEK stuff looks really nice... the big downside, as far as I can tell is that those units are not programmable giving me no control over set points for bulk, absorb and float cycles and then matching them with recommendations from VMAX. The 4215bn allows me to do this as well as set cutoff points for battery usage based on certain low set-point thresholds (i.e. Cut everything if battery bank goes below 12.2).

[norman_nomad]

First thing to do is check to see what Voltage your Alternator Regulator is generating. All vehicles and trucks today should be 14.2 volts. If you are using mechanical Battery Isolators you have no choice but to accept whatever the Alternator is providing.

However if you use a Electronic Battery Isolator made by Sure Power they have a Voltage Regulator built-In to control the Alternator Voltage to provide 14.4 volts for FLA and 14.2 for AGM

So the answer to your question is first make sure your Alternator Voltage Regulator is outputting 14.2 volts. Once you have that squared away there is nothing else you can do except take what you can get. The difference between 14.2 and 14.4 is not enough to make much if any difference except the length of time required. 14.4 will just be faster. FWIW 13.8 is even good, just slower.

If I had to guess your battery is deeply discharged, and your alternator just has not had enough time to bring the voltage up. Your vehicle alternator is capable of 16 volts if the Regulator will go that high. Blue Seas even sells Voltage Regulators for Marine engines to solve the problem fixed @ 14.2 volts.

14.2 is universal 12 volt battery charge voltage set by SAE for all Automotive and Marine applications. 14.2 volts is perfect for both AGM which the industry has switched to and drop in replacement LFP batteries. 14.2 was chosen because for 3 reasons.

1. Is at the Gassing Threshold Voltage. Any higher on a AGM makes it is likely to over charge, causing gas pressure to rise to high, and causing the battery to vent. Game over if that happens

2. 14.2 is perfect voltage to charge a LFP battery.

3. Also works for FLA batteries, just takes a little longer and will minimize gassing and water usage. Thing is with lead acid batteries, the lower the voltage you use, th elonger your battery last. Float at 13.6 to 13.8 is perfect, but can take 24 hours to recharge.

12.6 volts sounds like a fully charged battery not on a charger at rest.

Thanks for all of the great info Sunking!

Some quick notes, I'm getting 14v from the Bosch alternator according to the multi-meter. I've tapped from + on the starter post and run this line via 4 gauge wire into the cabin of the van (1.5ft of wire). This side connects to the Blue Seas ACR and shows 14v (so no loss on the way into the van as far as I can tell). The ACR, of course, links both batteries once the alternator is supplying it's charge voltage and disconnects when not running.

When the ACR connects the starter battery and leisure/solar battery bank, the voltage *drops* to ~13v. You are *correct* when you assumed my bank was run down. The leisure battery bank was hovering at 11.8v for a couple days while setting everything up and have been very anxious to get the batteries back to full charge before I shave off too much life. I'm assuming this voltage drop occurs because the voltage is now being shared amongst the starter battery (about 12.6v at rest) and the depleted leisure bank? I've watched the supply voltage from the alternator creep up from 13v to 13.3v while driving for 30min. Any feedback/corrections/illuminations here would be well received.

I've only driven the van twice since install (2 days ago) and only for about 30 min and was a bit discouraged to see the charge rise to and hold just barely 12.6v. These Vmax batteries are at 100% at 13v+. I suspect if I drive for a long while I can pack a bit more juice into the bank, but ... it sort of an exponential curve ...correct? The higher the bank charges up, the longer it needs to take on additional voltage assuming a constant input voltage.

I have 400 watts of solar and so the *idea* was to have the ACR available to avoid depleting the batteries below 12.2v during gloomy months and the solar would keep things topped off. I think this would work if I could get 13.8-14v when the ACR couples the batteries, but haven't seen that yet (possibly due to depleted leisure bank as mentioned above.. maybe I just need to drive it longer).

I guess I'm looking for best practices here. I'd like to keep the leisure bank topped off and charged at the thresholds supplied by the manufacture to keep me and the batteries unstressed and happy. I'm a bit too novice to know how this is being handled by others.

For reference, this is what VMax sent me:

Float: 13.7V
Bulk: 14.8V
Absorb: 14.5V

Any feedback/help appreciated.

[Sunking]

When the ACR connects the starter battery and leisure/solar battery bank, the voltage *drops* to ~13v. You are *correct* when you assumed my bank was run down. The leisure battery bank was hovering at 11.8v for a couple days while setting everything up and have been very anxious to get the batteries back to full charge before I shave off too much life. I'm assuming this voltage drop occurs because the voltage is now being shared amongst the starter battery (about 12.6v at rest) and the depleted leisure bank? I've watched the supply voltage from the alternator creep up from 13v to 13.3v while driving for 30min. Any feedback/corrections/illuminations here would be well received.

OK 11.8 volts is a DEAD BATTERY with no charge.

Afraid you do not quite understand how batteries charge, but that is OK I can walk you through the basics. When you connect a charger to a battery and set the voltage to 14.2 volts, DOES NOT MEAN you are going to see 14.2 volts. It depends on how deeply discharged the battery is. the Battery Internal Resistance and how much current you charger is capable of delivering. Example a 12 volt 200 AH Leisure Battery, with a resting voltage of 11.8 volts, Internal Resistance of .01 ohms and a 20 amp charger. Set the charger to 14.4 volts, connect it and you will only read 12 volts initially. After 10 to 12 hours the voltage will creep up on 14.4 volts and hold until Charge Current stops flowing. When current stops, the battery is charged up and Floating. Disconnect the charger and in a hour or so the voltage will read 12.6 volts indicating full charge.

So what you need to do is drive until you see the voltage level out and quit seeing charge current. Better yet get that Leisure battery on a charger and charged up immediately before it is to late, You never want to see your battery go below 12.1 volts at REST aka Open Circuit Voltage (OCV).

[norman_nomad]

OK 11.8 volts is a DEAD BATTERY with no charge.

Afraid you do not quite understand how batteries charge, but that is OK I can walk you through the basics. When you connect a charger to a battery and set the voltage to 14.2 volts, DOES NOT MEAN you are going to see 14.2 volts. It depends on how deeply discharged the battery is. the Battery Internal Resistance and how much current you charger is capable of delivering. Example a 12 volt 200 AH Leisure Battery, with a resting voltage of 11.8 volts, Internal Resistance of .01 ohms and a 20 amp charger. Set the charger to 14.4 volts, connect it and you will only read 12 volts initially. After 10 to 12 hours the voltage will creep up on 14.4 volts and hold until Charge Current stops flowing. When current stops, the battery is charged up and Floating. Disconnect the charger and in a hour or so the voltage will read 12.6 volts indicating full charge.

So what you need to do is drive until you see the voltage level out and quit seeing charge current. Better yet get that Leisure battery on a charger and charged up immediately before it is to late, You never want to see your battery go below 12.1 volts at REST aka Open Circuit Voltage (OCV).

Thanks Sunking. This is all very helpful.

So I was seeing 11.8v from my charge controller meter when running peripherals (just the 12v truck fridge) and so perhaps the true resting voltage was just slightly higher. In any case, this is still certainly too low and I do understand the importance to keeping the batteries at full charge at all times. Once the ACR was installed a couple days later, the battery bank has not dipped below 12.2.v. Still this is too close for comfort. I happen to be hitting the road in a couple days and will be driving 8-10 hours at a stretch and so the battery will get a proper full charge it seems (or close to it... and the 400 watt solar array will help me get to 100%)

I have 2 important questions for you:

1) The starter and leisure bank have different full-charge profiles. I know that the Vmax Leisure bank will hold 13v. The starter appears topped off at ~12.6 (as you've mentioned). When I run power to both from the alternator for a long period of time (let's say 8 hours of driving) will they be charged equally? Will the differing full-charge voltages between the two batteries cause a kind of problem?

2) Is there any risk in overcharging the leisure bank if it continues to see 14v - 14.2v from the alternator on a long drive? Vmax specifies float at 13.7v. I read your previous comment about the 14.2v gassing threshold voltage, but would appreciate any additional thoughts here.

[Sunking]

So I was seeing 11.8v from my charge controller meter when running peripherals (just the 12v truck fridge) and so perhaps the true resting voltage was just slightly higher. In any case,

Yes for the same reason i tis higher when charging. But on a 12 volt battery if your system is sized properly you should never see more than 0.2 drop on a heavy load, If you se more than that, then either your battery is to small, or going out.

I have 2 important questions for you:

1) The starter and leisure bank have different full-charge profiles. I know that the Vmax Leisure bank will hold 13v. The starter appears topped off at ~12.6 (as you've mentioned). When I run power to both from the alternator for a long period of time (let's say 8 hours of driving) will they be charged equally? Will the differing full-charge voltages between the two batteries cause a kind of problem?

OK good question and now we get down to the differences of a Mechanical Battery Controller and Electronic Isolator. In any Parallel Circuit, the voltage is equal. So if one reads 12.6 and the other is 13, put them in parallel and they have to equalize. Somewhere in the middle, one is going to cause a big inrush of current to the lower level cell. That is exactly what your mechanical relay does. A electronic Isolator does not have that problem.

2) Is there any risk in overcharging the leisure bank if it continues to see 14v - 14.2v from the alternator on a long drive? Vmax specifies float at 13.7v. I read your previous comment about the 14.2v gassing threshold voltage, but would appreciate any additional thoughts here.

Sure there is risk and will happen. But not much to worry about or anything you can do about it. Look SLI Batteries (starting-lighting-ignition) are different than a True Deep Cycle battery. They use different alloys and plate construction. They both charge the exact same way like any battery. The only difference is Float Voltages. But in a vehicle no battery is really a happy camper because automobiles follow standards and are locked in at 14.2 volts. Great for charging any lead acid battery type, Just ro high for float or extended driving. Again no real big deal as auto batteries are cheap, and Auto batteries are all switching to AGM, and AGM can handle 14.2 volts OK without venting. FLA can handle t but will use more water. Auto Manufacturers have chosen a voltage that yields rapid recharge of the SLI battery, and prevents sulfation.

Boils down to this. A fully charged battery is a balance act on a Razors Edge. On one side you have sulfation (under charged) and the other side is corrosion (over charged). You have to make a choice which side to live on. It is impossible to stay balanced Unfortunately Solar Users do not have a choice, 99% are on the Sulfation side because Solar is not capable of fully charging a battery. Mostly because all system are grossly undersized. Sulfated batteries are the root cause of roughly 90% of all premature battery failures. Auto Manufacturers chose Corrosion side which provides longer life and more energy.

Short story with mobile applications is you take what you get.

[norman_nomad]

Yes for the same reason i tis higher when charging. But on a 12 volt battery if your system is sized properly you should never see more than 0.2 drop on a heavy load, If you se more than that, then either your battery is to small, or going out.

Ahh... ok, good info. I've only ever watched the system drop 0.1v when running fridge, inverter and cabin lights. So I think I'm good. Nice to have this metric however.

OK good question and now we get down to the differences of a Mechanical Battery Controller and Electronic Isolator. In any Parallel Circuit, the voltage is equal. So if one reads 12.6 and the other is 13, put them in parallel and they have to equalize. Somewhere in the middle, one is going to cause a big inrush of current to the lower level cell. That is exactly what your mechanical relay does. A electronic Isolator does not have that problem.

Ok, I understand what you're saying. The Blue Seas ACR is creating a parallel circuit which shares voltage and thus equalizes which makes sense (and also what I've observed). An electronic isolator could treat each battery bank independently... which I guess would be more optimal if I wanted to treat each with different charge profiles. I'd like to keep the ACR for now.

I have one last question about shared charging, and we can be done with this part: Assuming my starter battery is at 12.6v and my leisure bank is at 12.6v and I run the vehicle for a long while, will both battery banks receive the same amount of current from the alternator in essence *charging* the leisure bank and *over-charging* the starter...OR... because the starter battery is fully charged, will it offer some level of resistance and instead direct the majority of the current to the leisure bank?

Boils down to this. A fully charged battery is a balance act on a Razors Edge. On one side you have sulfation (under charged) and the other side is corrosion (over charged). You have to make a choice which side to live on. It is impossible to stay balanced Unfortunately Solar Users do not have a choice, 99% are on the Sulfation side because Solar is not capable of fully charging a battery. Mostly because all system are grossly undersized. Sulfated batteries are the root cause of roughly 90% of all premature battery failures. Auto Manufacturers chose Corrosion side which provides longer life and more energy.

Ahh...ok thanks for the historical context... and it makes sense that manufacturers have had to make certain concessions given all of the moving parts and have chosen corrosion instead of sulfation.

I'd like to keep the ACR and could use advice on strategy: I considered purchasing an adjustable voltage regulator for my Bosch alternator. This would allow me to supply 14.5v - 14.8v from the alternator which would more rapidly charge the leisure bank. Would this be ill advised? Is there any way to attenuate this voltage on the starter end of the chain to feed just 14.2v to the starter battery (to avoid excess corrosion or venting on the starter battery which has no persistent demands put upon it and is only used for starting the vehicle)?

Or should I just be happy with 14.2v and let my 400 watts of solar cover the rest?

Thanks again for all the great info.

[Sunking]

[QUOTE=norman_nomad;n338545] I have one last question about shared charging, and we can be done with this part: Assuming my starter battery is at 12.6v and my leisure bank is at 12.6v and I run the vehicle for a long while, will both battery banks receive the same amount of current from the alternator in essence *charging* the leisure bank and *over-charging* the starter...OR... because the starter battery is fully charged, will it offer some level of resistance and instead direct the majority of the current to the leisure bank?

Batteries self regulate their charge. When you connect batteries in parallel, they will equalize. The higher state of charge will flow to the lower state of charge and Equalize. Think of it like a Democrat and you have money. Democrats will take your money away from you and give it away to the lazy and slackers after they take healthy commision for themselves.

Bottom Line here is in a mobile application like an RV there is no perfection, just compromises. A SLI battery is made differently than a Hybrid or Deep Cycle Battery. They have slightly different voltages. In a vehicle the Alternator is just a simple Regulator with 1 set voltage of 14.2 volts. 14.2 volts work on any kind of 12 volt batteries being lead acid or lithium. The main purpose is to quickly recharge a SLI battery as fast as it can be done. You have to work and live with it.

I'd like to keep the ACR and could use advice on strategy: I considered purchasing an adjustable voltage regulator for my Bosch alternator. .

The issue with Mechanical relays is someday soon your two batteries will not be equal in voltage, and as soon as you close the relay, the huge amount of current will weld the contacts together. You will not notice until that one day you have been parked camping a couple of days, go to start your RV and hear the dreaded Click Click. Not only are your house batteries dead, bu talso your SLI battery because it has been welded in Parallel with the house batteries. Game over.

I suggest you leave the regulators alone and leave them at 14.2 volts. Any higher and you risk serious damage to both your SLI and House Batteries.