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Old 18-12-2023, 10:57   #16
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Re: Will my alternator overcharge AGMs?

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Probably true, but my Balmar regular is in the small engine enclosure and about 1 foot away for the engine and it has been fine for 22 years. Just saying.
Yes, mine too. Well, its two feet away from the engine and only 4 years.
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Old 18-12-2023, 14:08   #17
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Re: Will my alternator overcharge AGMs?

Good on you, but over the years I have replaced 5 Balmars that were in the engine compartment and zero that were outside it
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Old 18-12-2023, 20:06   #18
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Re: Will my alternator overcharge AGMs?

Perhaps apropos of nothing, and I can't really put-my-finger-on-it, but over decades I've tended to have an uneasy feeling towards Balmar.
Maybe it's because since day one they've always had a campaign in which, "We are the absolute best at alternators/regulators and related gear and nobody else comes close".
It makes me think of a line in Hamlet, "The lady doth protest too much, methinks".
Only I change it to, "The company doth exalt itself too much, methinks".
Oh well, maybe I'm just rambling.
Carry on.
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Old 20-12-2023, 07:18   #19
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Re: Will my alternator overcharge AGMs?

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Yes AGM batteries are more sensitive to undercharging. That would be a problem if your only, or principle, charge source was your engine alternator. That is not the system you described.

Yes, AGM are damaged by overcharging. However, a properly set up alternator does not go high enough in voltage to cause this. Think about this for a second. Lots of cars use AGM batteries with dumb alternators. They can spend many more hours running than your boats engine.

If you want to regularly charge your batteries with your engine alternator, you need to have a smart regulator. That’s true for any battery, not just AGM. If you just pump some extra energy into the batteries as a side effect of running the engine, a dumb alternator will work fine.

My Lifeline AGM bank lasted 7 years, cycling virtually every day, charging from a dumb alternator when the engine was running. We move a LOT, and our engine runs about 500 hours a year. Is that good enough for you?
Thanks for this, it does sound reassuring. However, my other source of charging is, as I have already mentioned, a dumb 25A shore power AC/DC charger that runs at 14.5V when first turned on, then drops to 13.5V after 6 hours. Could this overcharge AGMs?

Edit, forgot to ask, what do you mean exactly by a properly set up alternator? As I mentioned, as far as I know my 55A alternator throttles back when it gets hot. That is as sophisticated as it gets.
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Old 20-12-2023, 07:29   #20
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Re: Will my alternator overcharge AGMs?

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If you motor for more than a couple of hours you simply -must- have an externally regulated alternator with a smart regulator. Every other option is technically flawed.

I can recommend a kit from Balmar, they have them for every engine.
I am uncertain as to how smart regulators work. According to Battery University "full charge is reached when the current decreases to 35 percent of the Ah rating". At that point full charging should stop or a float voltage should be applied. How does a smart regulator know that the current has decreased to 3-5 percent of the Ah rating? If there was no load, I can see how a smart regulator might do this, but I would likely have instruments, fridge, possibly autopilot running and lights running when motoring at night. How would a smart regulator know what was going into the battery and what was running instruments, etc?

Or do smart regulators take input from shunts? I can see that might work.
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Old 20-12-2023, 07:47   #21
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Re: Will my alternator overcharge AGMs?

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I am uncertain as to how smart regulators work.
They sense voltage, measure battery and alternator temperature, and have various programs based on the characteristics of various battery types. Here's what Balmar says about them: https://balmar.net/balmar-technology/
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Old 20-12-2023, 08:17   #22
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Re: Will my alternator overcharge AGMs?

I guess what I am trying to figure out is whether I should go for 2 new 90Ah sealed wet cell batteries, or spend ~40% more on 85Ah AGMs, given my likely usage and dumb charge setup. I cannot get higher capacity in my existing battery boxes and there is little scope to change this very easily. For AGMs to make sense for me, they need to last 40% longer than conventional sealed wet cell. How likely is that?

As I have said, my usage pattern would be to discharge the batteries when under sail and when using the windlass, using a separate LFP bank when at anchor. If I found the drop-in lithium bank worked well enough I could use that for extended sailing hours as well and so reduce the discharge of the lead acid bank. Ideally I would only use lead acid with the windlass and for emergency use if something happened to LFP, but I need experience and confidence with the LFP to reach that stage.

I know I could upgrade my LA charging setup, but I would prefer not to do that unless it gave me back real material benefit. I value the simplicity and robust nature of what I have and I have heard from a number of people who have had problems with external regulators. I would also prefer to spend money on more LFP capacity, or by just replacing the lead acids a little more freqently than I might otherwise have to if I had smarter charging kit.

I guess another thing I could do is to put in a smart shunt for the house bank to monitor the amps going in and out. Check it hourly when motoring and disconnect the bank when charged (along with my other hourly checks of weather, position, etc.). I would not turn off charging to the starter battery to mitigate the risk of blowing the alternator diodes. Would adding a smart shunt be worthwhile, or would I just be over engineering?

Although there is a lot of information online about AGMs and how to charge them, there is a lack of quantitative information. eg AGMs suffer more from under and over charging, but how much more? It would be great to see the results of some real tests for this sort of thing.
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Old 20-12-2023, 08:23   #23
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Re: Will my alternator overcharge AGMs?

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They sense voltage, measure battery and alternator temperature, and have various programs based on the characteristics of various battery types. Here's what Balmar says about them: https://balmar.net/balmar-technology/
Thanks. Interesting, but I wonder how reliable a guide to the SOC these characteristics are given the situation of a battery being charged, whilst the alternator is also supplying a load. Would a dumb alternator be just as good if backed up with SOC monitoring using a shunt?
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Old 20-12-2023, 10:06   #24
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Re: Will my alternator overcharge AGMs?

Considering you have a dumb charger, I would say to invest a minimum in batteries and save up to buy a good inverter/charger or even just a good charger before doing anything else.
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Old 20-12-2023, 12:07   #25
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Re: Will my alternator overcharge AGMs?

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My shore charger outputs 14.5V for 6 hours after powering up as well, then drops to 13.5V. ?
His charger is not all that dumb. and should work with AGMs.
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Old 22-12-2023, 08:37   #26
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Re: Will my alternator overcharge AGMs?

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My current house bank needs to be replaced. It consists of 2 85Ah SLA batteries which are basic wet flooded chemistry. I am considering replacing with AGMs for all the known advantages. However, my alternator outputs a regulated 14.5V and I am concerned this may overcharge my batteries and so shorten their life. My shore charger outputs 14.5V for 6 hours after powering up as well, then drops to 13.5V. Again a potential source for overcharging. The charging setup was designed with FLA in mind with any overcharging compensated for by topping up with water.

I keep the boat in the UK and the batteries stay cool much of the time, eg <20C, should that make any significant difference.

Whilst at anchor I intend to use a separate LFP bank, topped up with solar, so the AGMs should stay at a fairly high SOC most of the time, just used for instruments and auto pilot under sail, and when using the windlass.

Should I be concerned about my alternator overcharging, or just replace and not let it bother me?
Lots of opinions here, no doubt all better qualified than mine. However I'm in a similar position to you: about to replace SLA with Gel and AGM (AGM for start, and bow thruster; Gel for house). I have had similar concerns with alternator output. Because the investment in batteries will be quite high (about 1100Ah altogether), I feel its worth investing in gear that should ensure effective and safe charging.

The existing mains chargers already provide 3 and 4 step charging ie. effective charging and good protection.

All charging sources charge only the house bank; then 2 Victron Orion DC to DC chargers (about 160 each) charge the start and b/t batteries from the house bank.

A Sterling external regulator (PDARW at 260) ensures a proper 4-step charge for the house bank from the alternator.

So a bit costly (nearly 600) but they should be pretty future-proof even if I eventually go for Lithium.
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Old 22-12-2023, 16:00   #27
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Re: Will my alternator overcharge AGMs?

I struggle to understand why anyone would prefer AGM to gel batteries. The problems with AGMs, and especially with partial SOC charging (a normal part of cruising usage), are disqualifying as far as I'm concerned. I used quality gels (Sonnenschein) for two decades, with great experiences. In either case it is important to buy top quality - there are a lot of crappy AGMs and gels out there.

There really is no excuse for operating an alternator with a stock internal regulator on a cruising boat. Yes it costs a bit of money for an external regulator, but so does having to replace batteries prematurely and running the engine longer just to finish charging (which you would need to do with AGMs or suffer the cumulative effects of partial SOC charging). While in the past automotive alternators were regulated to a constant voltage, usually around 13.7V, modern alternators do often operate over, and even well over, 14V. Even if that voltage is below the max rating of the batteries, keeping them at that voltage will shorten battery life. Of course such a system will work (as opposed to immediately breaking) but in the long run it will be inefficient and require more frequent battery replacements. So just bite the bullet and put in a proper external regulator.

Internal regulators monitor alternator temperature and reduce output to prevent overheating. If the internal regulator is bypassed or removed then the new regulator must sense alternator temperature to provide the same protection. At least one external regulator leaves the internal regulator in place and functioning, so it doesn't need to solve that problem. A separate issue that seems to get confused with this one is that the battery temperatures should be monitored by the regulator, especially if a large alternator is used relative to the battery bank size.

In the old days with 13.7V alternators an external regulator could be used to boost charging by simply adding a voltage drop into the regulator's voltage sense, fooling it into operating at a higher voltage. This could be as simple as a resistor. Such regulators do not have the ability to reduce 14V+ output of modern alternators by raising the sensed voltage, and so are not so relevant today.

Fortunately my V-P D2-40F diesel engine came with a Mitsubishi 115A alternator - more than enough for my installation - which has an external voltage sense for the internal regulator. (The sense lead extends outside the case, and as shipped is connected to an external sense terminal. It is easy to connect it instead to an external regulator, or to bypass isolation diodes, without opening the alternator.) The internal regulator provides thermal management of the alternator, while the external Nordkyn VRC-200 manages the output to the batteries (with the optional use of a current shunt and battery temperature sense). This regulator can drive alternator output either higher or lower than the stock output voltage, and can handle lithium charging (the reason it was developed) as well as the usual lead battery profiles. At least for my application this is the best alternative that I could find. Also, in the event of the failure of the external regulator it is a simple matter of switching the sense lead back and original operation is restored.

Greg
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Old 23-12-2023, 01:13   #28
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Re: Will my alternator overcharge AGMs?

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I struggle to understand why anyone would prefer AGM to gel batteries. The problems with AGMs, and especially with partial SOC charging (a normal part of cruising usage), are disqualifying as far as I'm concerned. I used quality gels (Sonnenschein) for two decades, with great experiences. In either case it is important to buy top quality - there are a lot of crappy AGMs and gels out there.

There really is no excuse for operating an alternator with a stock internal regulator on a cruising boat. Yes it costs a bit of money for an external regulator, but so does having to replace batteries prematurely and running the engine longer just to finish charging (which you would need to do with AGMs or suffer the cumulative effects of partial SOC charging). While in the past automotive alternators were regulated to a constant voltage, usually around 13.7V, modern alternators do often operate over, and even well over, 14V. Even if that voltage is below the max rating of the batteries, keeping them at that voltage will shorten battery life. Of course such a system will work (as opposed to immediately breaking) but in the long run it will be inefficient and require more frequent battery replacements. So just bite the bullet and put in a proper external regulator.

Internal regulators monitor alternator temperature and reduce output to prevent overheating. If the internal regulator is bypassed or removed then the new regulator must sense alternator temperature to provide the same protection. At least one external regulator leaves the internal regulator in place and functioning, so it doesn't need to solve that problem. A separate issue that seems to get confused with this one is that the battery temperatures should be monitored by the regulator, especially if a large alternator is used relative to the battery bank size.

In the old days with 13.7V alternators an external regulator could be used to boost charging by simply adding a voltage drop into the regulator's voltage sense, fooling it into operating at a higher voltage. This could be as simple as a resistor. Such regulators do not have the ability to reduce 14V+ output of modern alternators by raising the sensed voltage, and so are not so relevant today.

Fortunately my V-P D2-40F diesel engine came with a Mitsubishi 115A alternator - more than enough for my installation - which has an external voltage sense for the internal regulator. (The sense lead extends outside the case, and as shipped is connected to an external sense terminal. It is easy to connect it instead to an external regulator, or to bypass isolation diodes, without opening the alternator.) The internal regulator provides thermal management of the alternator, while the external Nordkyn VRC-200 manages the output to the batteries (with the optional use of a current shunt and battery temperature sense). This regulator can drive alternator output either higher or lower than the stock output voltage, and can handle lithium charging (the reason it was developed) as well as the usual lead battery profiles. At least for my application this is the best alternative that I could find. Also, in the event of the failure of the external regulator it is a simple matter of switching the sense lead back and original operation is restored.

Greg
At the risk of thread creep: do you use gel successfully for high cranking loads ie. start or bow thruster?
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Old 23-12-2023, 02:29   #29
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Re: Will my alternator overcharge AGMs?

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At the risk of thread creep: do you use gel successfully for high cranking loads ie. start or bow thruster?
I use the gels for starting and for the anchor windlass, in addition to the house needs. For the starter just confirm that the batteries' Cold Cranking rating (amps) is sufficient. It was not even close for Carina. I would use the same standard with the windlass, although I always run the engine when raising the anchor. Gels (and AGMs) have very low internal resistance so are able to provide a higher current (and charge faster) than flooded batteries, and have lower voltage sag under high loads as well.

The thing to remember is that the actual amount of power required to start the engine or lift the anchor is quite small; it is a high load for a very short time. Running a starter, even a 100A one, for 5 seconds is only 0.08Ah. Running a 100A windlass for 3 minutes is 5Ah. The smallest battery you are likely to use is about 100Ah, so these loads barely make a dent in the SOC.

FWIW I used three gel batteries, each rated at about 100Ah. (The starter on my little engine at the time was probably around 60A.) I had them arranged in two banks, which was only so that I would have a fallback if one bank failed. At this point I am considering putting all batteries into one bank and be done with it. With a lithium jump starter as backup that would be sufficient. In the years I have cruised I never have let a bank go too low to start the engine. YMMV

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Old 23-12-2023, 22:22   #30
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Re: Will my alternator overcharge AGMs?

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I guess what I am trying to figure out is whether I should go for 2 new 90Ah sealed wet cell batteries, or spend ~40% more on 85Ah AGMs, given my likely usage and dumb charge setup. I cannot get higher capacity in my existing battery boxes and there is little scope to change this very easily. For AGMs to make sense for me, they need to last 40% longer than conventional sealed wet cell. How likely is that?
Question, when was the last time you worried about the SLA battery in your car over charging?

I would fit SLA batteries from one of the better suppliers in the UK. No longer a fan of Tanya after they supplied a pair of Rolls FLA with a thick layer of dust on top and only half charged. Today we now use a Bosch 95Ah AGM for engine starting. Its probably made in the same factory as Varta (Johnson Controls) and looks remarkably similar, so just a different label. I only chose an AGM because it was second hand but unused after someone bought the wrong size. I doubt we will see any difference between this and a good quality SLA in use.

You have a 55A internally regulated alternator and as the article Stu linked to says they will only accept a certain amount of current dropping quickly as they are charged up. So unlikely to be over charged. What charge is supplied will go to powering all the items you have running whilst at sea. That can be 10A for us with auto pilot, chart plotters, VHF and AIS etc.

I would however, fit a decent battery monitor if you don't already have one. We have the Sterling Power Mgmt, but that is what was available 16 years ago. Today I would probably chose the Victron BMV 712 because the Bluetooth option is really nice to have and monitor from the helm on a smart phone. Just be aware that they wander out of sync after a while as does my Sterling, but easily reset with a 100% charge.

If later you decide to upgrade to a LifePO4 domestic bank, then plan to do a complete review of the electrical system and how you are going to charge it etc. We had to give up the space under the saloon berths to fit our LFP, because like you we have limited space in the battery boxes. Since the space is a pain to get to with all the cushions, we rarely used it so wasn't a problem.

Pete
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