With the "rolling blackouts" that are happening and predicted, maybe a couple lithium batts plus converting your home appliances to 12V might be in order.
AGM battery charging/discharging (1 Viewer)
- Thread starter jgranthevagrant
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- #22
My reasoning for going with AGM for the house battery was the great longevity I have had with my AGM starting batteries. Averaging more than 5 years before any noticeable drop in performance. I did make sure my winch cables were long enough to switch to my starting battery if that is ever an issue. Winch does not get used that often. I did two short drives with the new battery this weekend. Alternator seemed to be charging it normally. Resting voltage seemed to be about 13.5 volts, if voltmeter is to be believed. I have not had time to do much research on solar or even home chargers, but I will get on that.
Suggestion: Get a multimeter.
That's about what mine reads, but of course, it varies according to how long it's been setting without engine running or solar hooked up. With engine running, I've seen it as high as 15 volts. My starting batt is the old school lead/acid and will read about 14.6 volts with engine running. I've thought about the same issue with the length of my winch cables when I installed it and they will reach my starting batt in an emergency, but I'd be cutting a few wire ties...
Being that my 80 is not my daily driver, it can set for weeks at a time and with gas prices on the rise, I can't see that changing. This AGM is the 3rd aux batt I've had since about 2002 when I installed the 2nd battery box and isolator. The previous were lead/acid deep cycle or marine type, but this AGM has lasted the longest. It's been doing the job since 2013 without fault. I see no need to "upgrade" to anything else.
^^^ I would be very surprised that a lead acid battery -whether AGM or not- would have a resting voltage of 13.5V if by resting you mean the usual "when the temporary charging effects such as surface charge have dissipated".
^ If my alternator were giving out 15V I would look into it / be concerned.
^ If my alternator were giving out 15V I would look into it / be concerned.
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- #26
I have never seen my alternator go past 14.4 or so, again if the voltmeter attached to the system is to be believed. I have 3 multimeters. One for boat motors, one for home, and one that is always on the truck. I go to them pretty often to doublecheck the other meters. I'm not sure what the house AGM is supposed to be at for resting voltage.
My temperature compensating alternator puts out high 13.x V when cold and mid 13.x V when warm. The resting voltage of a fully charged flooded lead acid battery is ~12.6V
I would be concerned if your alternator was putting out more than 14.4V or if your fully charged FLA battery resting voltage was more than 12.6V.
Have you modified your factory charging system at all (e.g. diode)?
EDIT: found this on the internet. I guess fully charged AGM resting voltage is 13V if this is to be believed.
I would be concerned if your alternator was putting out more than 14.4V or if your fully charged FLA battery resting voltage was more than 12.6V.
Have you modified your factory charging system at all (e.g. diode)?
EDIT: found this on the internet. I guess fully charged AGM resting voltage is 13V if this is to be believed.
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^ yes, that is right. The AGMs show slightly higher voltage than the FLAs. Out of curiosity, I just went out and checked an AGM battery that I have had stored unused for at least 2 or 3 weeks after charging, maybe more, and it showed 12.96V at about 80F. That is also why I charge it at 14.6V for bulk, not the usual 14.4V that I use for FLAs. (And OTOH I have never seen a FLA showing more than 12.6 or 12.7V at normal room temps after resting.)
To be clear, when I am talking about resting voltage, I mean something like several hours or a day after a charge, not just a few minutes.
It is worth noting that these resting voltages are inherent to the physical chemistry of the materials pair, nothing much you can do about those. (Of course, they are a function of the temperature and the level of charge but different story.) The common 14.4V of the charger / alternator during bulk charging OTOH is an arbitrary setting chosen by the manufacturer (because it makes sense for those materials). So it is entirely possible that a charger or an alternator would be poorly designed / out of specs / damaged / odd and give a different voltage (like 15V or more), but such a high voltage would be something to look into IMO if it's just a common alternator. That is also why I think that your usual alternator is set for 14.4V because the manufacturer expects you to use a FLA as a starter battery. Departing from that assumption by substituting other types of batteries may then give rise to problems. And that is also why relying on a typical 14.4V alternator to charge an AGM battery may not be optimal as far as keeping the AGM fully charged. (I'm talking about dumb alternators here.)
Now, having said all that, I also must admit that I don't know much about alternator design. I would be interested in knowing if there is a way to adjust the max voltage produced, maybe by tweaking something on the boards. Anybody knows?
But assuming it is not easily modifiable (I never heard it is TBH), that is also why a typical added charge controller (like a solar one or a DC-DC in vehicle charger) is useful for AGMs, because you can likely easily set up the charging cycle for specific AGM voltage needs with some of those.
Added: on a related note, I would suggest that if somebody considers getting a DC - DC charger or a solar controller to deal with their house battery, that they may want to ensure that it does indeed include settings for LiFeP since it seems likely that those will be the next prevalent type of batteries. (Personally, I've already begun to switch to those. Not planning to buy an AGM any more TBH.)
To be clear, when I am talking about resting voltage, I mean something like several hours or a day after a charge, not just a few minutes.
It is worth noting that these resting voltages are inherent to the physical chemistry of the materials pair, nothing much you can do about those. (Of course, they are a function of the temperature and the level of charge but different story.) The common 14.4V of the charger / alternator during bulk charging OTOH is an arbitrary setting chosen by the manufacturer (because it makes sense for those materials). So it is entirely possible that a charger or an alternator would be poorly designed / out of specs / damaged / odd and give a different voltage (like 15V or more), but such a high voltage would be something to look into IMO if it's just a common alternator. That is also why I think that your usual alternator is set for 14.4V because the manufacturer expects you to use a FLA as a starter battery. Departing from that assumption by substituting other types of batteries may then give rise to problems. And that is also why relying on a typical 14.4V alternator to charge an AGM battery may not be optimal as far as keeping the AGM fully charged. (I'm talking about dumb alternators here.)
Now, having said all that, I also must admit that I don't know much about alternator design. I would be interested in knowing if there is a way to adjust the max voltage produced, maybe by tweaking something on the boards. Anybody knows?
But assuming it is not easily modifiable (I never heard it is TBH), that is also why a typical added charge controller (like a solar one or a DC-DC in vehicle charger) is useful for AGMs, because you can likely easily set up the charging cycle for specific AGM voltage needs with some of those.
Added: on a related note, I would suggest that if somebody considers getting a DC - DC charger or a solar controller to deal with their house battery, that they may want to ensure that it does indeed include settings for LiFeP since it seems likely that those will be the next prevalent type of batteries. (Personally, I've already begun to switch to those. Not planning to buy an AGM any more TBH.)
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You can add a diode in the alternator voltage sensing circuit. That will create a small voltage drop causing the alternator to think the voltage is lower than it actually is and in turn cause it to increase the charge voltage.
Here is an example
HKB Electronics
The Alternator Voltage Booster was the first of its type on the market and is the only unit available that was has been purpose built for alternator voltage boosting.
www.hkbelect.com
^ yes, that would be about 0.6V for a silicon diode I imagine. Brute force! I like it! Although, I was thinking more along the lines of a pot someplace on the ICB to fine tune things.
The inherent problem with those approaches, though, is that it still does not deal well with having 2 different types of batteries connected directly to the same alternator. Interestingly, though, in the case of OP he is in a unique situation because he has 2 separate alternators IIRC, so he could modify only one of them. Yet, adding a whole 0.6V may be a bit much for an AGM.
I should add that one thing that just boggles my mind is that a LiFeP battery will actually respond pretty well to charging at 14.4V as well, so in a pinch it could charge OK (if not optimally) with the usual 14.4V alternator as well. Very convenient! What were the chances of that...?
The inherent problem with those approaches, though, is that it still does not deal well with having 2 different types of batteries connected directly to the same alternator. Interestingly, though, in the case of OP he is in a unique situation because he has 2 separate alternators IIRC, so he could modify only one of them. Yet, adding a whole 0.6V may be a bit much for an AGM.
I should add that one thing that just boggles my mind is that a LiFeP battery will actually respond pretty well to charging at 14.4V as well, so in a pinch it could charge OK (if not optimally) with the usual 14.4V alternator as well. Very convenient! What were the chances of that...?
They do make an adjustable one that is lower. It is important to note that the whole vehicle will see the elevated voltage, including ECUs which may cause issues. I haven't heard of any issues though.
This is generally used for a charging a single AGM that replaced the stock FLA. For dual battery systems with mixed types, the second battery would most likely need to use a DC-DC charger or something.
Thanks for the heads up. So as to not hijack thread I'll look into it. Prelim research points to possible voltage regulator in alternator. Being that it's 27 yrs old and only thing I've done is replace brushes about 100k miles ago, I can't complain.
^ well, I do know that some DC-DC chargers do allow settings up to 15V and maybe higher but I don't think it's good to charge a FLA and likely not even an AGM at 15V for more than a short time.
What you could easily do to check this is to run down the battery a bit with the headlights, engine off, then start the engine with the low battery and see what voltage the alternator produces then.
What you could easily do to check this is to run down the battery a bit with the headlights, engine off, then start the engine with the low battery and see what voltage the alternator produces then.
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- #34
Lots of good info here. My separate alternator and house battery means the whole house system is separate from things like the ECU at all times. I like that. When I put the second alternator in, I tried to mimic the OEM alternator circuit, right down to the fusible link, fuses, and the diode circuit that is normally run through the dash. I got the fuses and fusible link no problem, but I never found a good way to mimic the diode circuit. AFAIK, the diode circuit only kicks off a warning light in the dash if there is an alternator malfunction. Monitoring the alternator output with the voltmeter as I drive should tell me if there is some sort of malfunction. I do notice that there are differences in voltage depending on how discharged the aux battery is and on engine revs. I have never seen the voltage on the voltmeter go past 14.4. I probably checked the resting voltage less than an hour after parking. I will go out and check it again at some point, and maybe double check it with the multimeter.
well, coming back to the original post, you got a new battery, great. Most important part there. Now to try and make sure it does not go bad fast again, I would suggest thinking about not using the winch with it, and trying to charge it to the higher level that is typically recommended for (needed by?) AGMs. You could try to do the latter with the diode trick on the second alternator, but a full extra 0.6V seems a bit excessive to me. Or bite the bullet and get a DC-DC charger that has good (adjustable) charge settings for your AGM. If you think you may want to put in solar later on, you can get (I think) a DC-DC charger that can also accept a solar panel input (but how well they do that, I don't know). Unfortunately, I doubt those are inexpensive.
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- #36
I have had my eye on the Redarc stuff for a while. I think I will try to get a better 110v charger for when the the truck is sitting at home, and hold off on the DC to DC charger until I have an idea and budget for solar. Winching will be limited no matter what, and I can do that with motor running and/or switch the winch to the starting battery. I just checked the aux battery, which has been sitting for a couple of days with no draw. Blue Sea voltmeter reads 12.76 volts, and multimeter reads 13.72 volts. Battery was fully charged with a 110 charger before installation. Blue Sea meter is about 1.5 metres from the battery and multimeter was right beside the battery.
measuring voltage is very easy electronics-wise, any cheapo voltmeter or multimeter should measure easily well within 0.1V error if not defective. You have a huge difference there. A difference in principle could be explained with something going on with the Blue Sea (ongoing load or measuring the starter battery instead, etc). But then again, why would the house battery voltage be 13.7V a couple of days after charging if it's a Lead Acid? Never heard of an AGM that does that. So either I don't know enough about batteries (certainly true), am missing something (likely), and/or there is something wrong with your multimeter (unlikely). Have you tried putting the multimeter on the Blue Sea contacts and verify they give the same reading?
added: had assumed from what I read that you meant a couple of days since charging, but is it that the battery had just been charged by the alternator maybe? If so, then sure it could be 13.7.
added: had assumed from what I read that you meant a couple of days since charging, but is it that the battery had just been charged by the alternator maybe? If so, then sure it could be 13.7.
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- Thread starter
- #38
Yes, I was curious about the difference between the Blue Sea voltmeter and the multimeter. I will check it again tomorrow. Blue Sea is only wired to the house battery. I have not tried the multimeter at the contacts either. The Blue Sea meter is in a little panel with a switch, USB ports and a 12volt cigarette lighter port. There is a fuse box between the aux batt and the panel, fridge, water pump, etc.
if it's a little built-in panel, it's likely that the 12V lighter port and the voltmeter are directly connected right there, so to avoid having to pull the panel or voltmeter out, you could just check the voltage across the lighter receptacle from the outside with the multimeter and that should be what the voltmeter sees as well. (Watch out for shorting it with your probes accidentally.)
