BBQ! (Basic Battery Question)

[Urlauber]

Pete, thanks for your reply. I know most of that, was hoping there would be a common + somewhere that I could slip through the Hall sensor. May not work out.

George, yeah I had those first, but figured I want to step up to one that shows both directions. Plus the ones I had only did 100A and this one goes up to 200 for a bit more room.

[Urlauber]

So, with the Sun getting a bit more intense, solar panel assisted voltages have been rising.

Recently, batteries are getting up to 14.5V. Is that harmful to the AGM batteries? This is without any (larger) loads on them. I have the fan running to suck out some heat, but that's no match for the 190W panel.

Just wondering if there is somewhere a cutoff that I have to set. The Solar Charge Controller is set to "AGM" for what it's worth.

And YES I measured the voltages with a Volt-Meter to make sure the BMPro isn't full of it. For example, my propane is really at 3/8th and sometimes it just shows full for some reason. Mysteries galore.

[booster]

Originally Posted by Urlauber

So, with the Sun getting a bit more intense, solar panel assisted voltages have been rising.

Recently, batteries are getting up to 14.5V. Is that harmful to the AGM batteries? This is without any (larger) loads on them. I have the fan running to suck out some heat, but that's no match for the 190W panel.

Just wondering if there is somewhere a cutoff that I have to set. The Solar Charge Controller is set to "AGM" for what it's worth.

And YES I measured the voltages with a Volt-Meter to make sure the BMPro isn't full of it. For example, my propane is really at 3/8th and sometimes it just shows full for some reason. Mysteries galore.

There are lots of threads with the proper charging of AGMs on this forum, but in generally the absorption stage is commonly speced by the manufacturers somwhere between 14.3 and 14.7v so I doubt the voltage by itself is a problem. But if you held all the time or even a lot of the time anything over float voltage (13.2-13.5v for most callouts) you can damage AGMs. It all is based on when the batteries actually get to full when on the higher voltage. The spec is usually based on looking at the amps going to the battery to tell when it is full, but very people do that even though it is best. Most chargers go by time or an algorithm but they are not very accurate. Most people don't have a choice but to do the charging that way. In general, unless the discharge is very small or nonexistent, solar has trouble overcharging a reasonable sized bank of batteries. The exception is if the batteries are already full from a long drive or other charging you would not want anything higher than float from the start of the solar charging so you don't overcharge the AGMs.


Depending on the solar controller, it may go right to float if the batteries are near full, as that is the safe way for it to look at it. But some controllers always run a full charge based on time usually and that can be very bad to do repeatedly on full batteries.


So what I am saying is 14.5v isn't bad, but overcharging is at that voltage.

[Urlauber]

Thank you, as always, for your quick, and as usual well written response! I will be able to sleep better, knowing that I am not cooking them AGM's. In the mornings, the voltage drops to 12.8V or so, and it's around noon when they reach that high level.

Sometimes the Solar Charge Controller decides that the battery is full, and shuts down. The voltage then hovers around 13.5V.

I actually try to turn off the main switch to prevent charging them when driving home from a trip. That way the solar panel can do it's thing over the week until needed again. Keeping the refrigerator running would be a good way to throttle the voltage a bit, but not sure if running it 24/7 is a good idea, or will reduce its life span.

[Urlauber]

After reading your post for a couple more times and thinking about it, this is how I imagine it works:

If the solar charge controller "thinks" the battery is full, it will drop down to ~13.5V and float charge it from there. If it thinks the battery needs topping off, it goes to ~14.5V until it changes its mind and considers it full.

Is this it, sort of super simplified?

The charge controller panel shows Amps, but that may be what the panel is delivering, not necessarily what goes into the battery? Or how does the controller limit current? Agh, so many questions, so little time.

[booster]

Originally Posted by Urlauber

After reading your post for a couple more times and thinking about it, this is how I imagine it works:

If the solar charge controller "thinks" the battery is full, it will drop down to ~13.5V and float charge it from there. If it thinks the battery needs topping off, it goes to ~14.5V until it changes its mind and considers it full.

Is this it, sort of super simplified?

The charge controller panel shows Amps, but that may be what the panel is delivering, not necessarily what goes into the battery? Or how does the controller limit current? Agh, so many questions, so little time.

The direct to 13.5v if the charger thinks the battery is full is common, but not all chargers do that, especially solar controllers so you have to read the literature to find out if yours works that way.


You are correct on the amps reading on the charger itself. Most chargers that do that readout are showing all the amps that are leaving the charger and the charger has no idea where they go. The only way to know the amps to the battery is to use a battery monitor that runs off a shunt at the battery. IMO, everyone should have a monitor in place to keep track of SOC and charging items, but some people don't agree and don't use one.

[RTRanger]

I’ve used a Magnum system with their battery monitor and a Victron system in past RVs. It is nice to have and integrated system. I think it is very important to have a battery monitor so you know the state of charge.

We now have a Roadtrek Ranger and this time I installed a $80 battery monitor (with Bluetooth and free app) that I got off of Amazon. It is nice, it works great, and seems very accurate. I’m going to put the display in the dashboard. This monitor can work with any type of battery. I’m running 200 amp hours of lithium.

Just thought I’d mention it for those reading this thread. Here is a link for the Goupchn 400A Battery Monitor, DC Voltage and Current Coulometer:
https://www.amazon.com/gp/aw/d/B09GYG4WLW

It appears to be sold by a number of other companies too.

[Urlauber]

I have to find the "common ground" to position the shunt. Not easy with two batteries, poles that look like octopuses, and 5" ground clearance. One of these days...

[booster]

Originally Posted by RTRanger

I’ve used a Magnum system with their battery monitor and a Victron system in past RVs. It is nice to have and integrated system. I think it is very important to have a battery monitor so you know the state of charge.

We now have a Roadtrek Ranger and this time I installed a $80 battery monitor (with Bluetooth and free app) that I got off of Amazon. It is nice, it works great, and seems very accurate. I’m going to put the display in the dashboard. This monitor can work with any type of battery. I’m running 200 amp hours of lithium.

Just thought I’d mention it for those reading this thread. Here is a link for the Goupchn 400A Battery Monitor, DC Voltage and Current Coulometer:
https://www.amazon.com/gp/aw/d/B09GYG4WLW

It appears to be sold by a number of other companies too.

Re the meter in the link. Does it do the automatic reset to zero at recharge like the Magnum and Victron do? I have found that many of the units that are in the that range of price are strictly coulome counters without the reset function. On your lithiums it isn't quite as bad as with lead acid batteries because the charge efficiency is close to 100% on lithium but still inaccurate over time. AGM charge efficiency is larger and variable on on depth of discharge.


We also have a Magnum monitor built in to the remote panel and it is very handy to have as a monitor, but IMO even more useful is that the Magnum can control the charging off of the monitor readings which makes amps based charging possible for the best in charge control, especially for AGMs.


We did have a monitor on a two battery setup where they are not in the same place (Roadtrek Chevy) and the combining of the grounds is not really much hassle once you identify a good place for the shunt.

[SteveJ]

Originally Posted by RTRanger

I’ve used a Magnum system with their battery monitor and a Victron system in past RVs. It is nice to have and integrated system. I think it is very important to have a battery monitor so you know the state of charge.

We now have a Roadtrek Ranger and this time I installed a $80 battery monitor (with Bluetooth and free app) that I got off of Amazon. It is nice, it works great, and seems very accurate. I’m going to put the display in the dashboard. This monitor can work with any type of battery. I’m running 200 amp hours of lithium.

Just thought I’d mention it for those reading this thread. Here is a link for the Goupchn 400A Battery Monitor, DC Voltage and Current Coulometer:
https://www.amazon.com/gp/aw/d/B09GYG4WLW

It appears to be sold by a number of other companies too.

Interesting unit, particularly with the Bluetooth to help with setup.

Question, the display looks pretty busy for a 2.4" unit, how is it working out in real life? I'm thinkin' a bit of squinting close up would be required?

I did notice in the description that it does reset to zero.

The temp sensor is nice if you don't have one incorporated elsewhere but one really should have a sensor for the controller.

[off topic] It's been about a year and a half since we replaced our Roadtrek with a Safari Trek. I still enjoy popping in here to keep up on interesting topics and to follow along posts from some people that are quite knowledgeable on "stuff".

[/off topic]

[booster]

Originally Posted by SteveJ

Interesting unit, particularly with the Bluetooth to help with setup.

Question, the display looks pretty busy for a 2.4" unit, how is it working out in real life? I'm thinkin' a bit of squinting close up would be required?

I did notice in the description that it does reset to zero.

The temp sensor is nice if you don't have one incorporated elsewhere but one really should have a sensor for the controller.

[off topic] It's been about a year and a half since we replaced our Roadtrek with a Safari Trek. I still enjoy popping in here to keep up on interesting topics and to follow along posts from some people that are quite knowledgeable on "stuff".

[/off topic]

I hadn't gone down far enough for the full description. oops


That said it would be interesting to see the manual to see what they say about how the calibration is done. If it just resets when it hits 100% and stays there until discharging again (to have it ignore the current going in during float) that is only part of it. To be accurate, they need to look at current and voltage to determine when the batteries are actually full and both the voltage and current need to be settable by the user to match the batteries. This is essential for lead acid and a nice feature, IMO, for lithium.


I don't see a "fully charged" indicator on the display so it is kind of unlikely that it does that settable calculation but not certain. Our Magnum does not set a fully charged indicator either, so you need to see the voltage to tell you are full when it goes to float.



As I mentioned, the devil in the details for battery monitors so you do need to know exactly how they are coming up with their readings. This is the most important during recharge when charge efficiency and tapering charge rates are happening. Just because a monitor hits 100% doesn't necessarily mean the batteries are really full, just that same amount has been put in as was taken out, so any losses in recharging due to inefficiencies are truly lost but not noticed by some monitors.

[SteveJ]

Originally Posted by booster

Re the meter in the link. Does it do the automatic reset to zero at recharge like the Magnum and Victron do? I have found that many of the units that are in the that range of price are strictly coulome counters without the reset function. On your lithiums it isn't quite as bad as with lead acid batteries because the charge efficiency is close to 100% on lithium but still inaccurate over time. AGM charge efficiency is larger and variable on on depth of discharge.


We also have a Magnum monitor built in to the remote panel and it is very handy to have as a monitor, but IMO even more useful is that the Magnum can control the charging off of the monitor readings which makes amps based charging possible for the best in charge control, especially for AGMs.


We did have a monitor on a two battery setup where they are not in the same place (Roadtrek Chevy) and the combining of the grounds is not really much hassle once you identify a good place for the shunt.

We've been using a monitor similar to this(there are several that appear identical under different brand names), in our Trek. We do boondocking for up to 2+ months at a time without plugging in. I've noticed no creeping of WH available. from what I've seen there is no provision to allow for the Peukert effect but it does reset so no apparent issue. For the low $$ it works fine with our two group 31 FLA batteries, I think.

https://smile.amazon.com/AiLi-Voltme...s%2C178&sr=8-3



We used two of the cheaper one way coulometers(one for each direction of current flow) in the RT which did have a building spread in the WHs in/out.

Link:

https://smile.amazon.com/bayite-6-5-...%2C178&sr=8-34

Have fun, y'all.

[booster]

Originally Posted by SteveJ

We've been using a monitor similar to this(there are several that appear identical under different brand names), in our Trek. We do boondocking for up to 2+ months at a time without plugging in. I've noticed no creeping of WH available. from what I've seen there is no provision to allow for the Peukert effect but it does reset so no apparent issue. For the low $$ it works fine with our two group 31 FLA batteries, I think.

https://smile.amazon.com/AiLi-Voltme...s%2C178&sr=8-3



We used two of the cheaper one way coulometers(one for each direction of current flow) in the RT which did have a building spread in the WHs in/out.

Link:

https://smile.amazon.com/bayite-6-5-...%2C178&sr=8-34

Have fun, y'all.

What settings does that two way meter allow you to do? That will normally give a pretty good idea how they are doing the reset calibration.


IMO, Peukert is a non issue and more or less a bogus thing for most RV setups because we don't have consistent discharge rates. I put Peukert at 100% on our meters, which gives more accurate actual SOC readings on discharge cycles.


What is the the very important factor is the charge efficiency, but the units with settable charge efficiency don't really handle it well with that setting because depth of discharge changes the recharge charge efficiency and we all have varying depths of discharge. That leaves the only way to really tell if the batteries are full to generate a 100% reset is to look at the ending charge parameters given by the battery manufacturers. These would normally be a time held at absorption voltage and being below amp reading at the same time. Both those settings need to settable to be accurate. This is critical in AGM applications and nice to have for lithium, although many using lithium go be voltage only.

[SteveJ]

Originally Posted by booster

What settings does that two way meter allow you to do? That will normally give a pretty good idea how they are doing the reset calibration.


IMO, Peukert is a non issue and more or less a bogus thing for most RV setups because we don't have consistent discharge rates. I put Peukert at 100% on our meters, which gives more accurate actual SOC readings on discharge cycles.


What is the the very important factor is the charge efficiency, but the units with settable charge efficiency don't really handle it well with that setting because depth of discharge changes the recharge charge efficiency and we all have varying depths of discharge. That leaves the only way to really tell if the batteries are full to generate a 100% reset is to look at the ending charge parameters given by the battery manufacturers. These would normally be a time held at absorption voltage and being below amp reading at the same time. Both those settings need to settable to be accurate. This is critical in AGM applications and nice to have for lithium, although many using lithium go be voltage only.

Here is a PDF of the manual

file:///C:/Users/iride/Downloads/Low%20Price%20Ali%20battery%20Monitor.pdf


There is no efficiency setting. I'm thinking that there is a formula locked inside that it uses for this. One "feature" is that it only shows about 202 to205 AHs when the controller goes to float. Also the same case when plugged in but after a few days of being plugged in on float the monitor will climb to 210. The charge inverter being used is an old(circa '9 multi stage Heart Freedom 10.

The only adjustments are for capacity and "zero voltage". The zero V adjustment will let you set a voltage amount that the monitor would see as zero. I didn't do that, left it at the default of 0.

While this unit doesn't integrate at all with my Victron SmartSolar controller it does appear to give out usable data. Though maybe not dead on, it does seem to be repeatable and it seems to work OK. I do know that it's better than nothing and better than the old dual one way monitors that we used in the RT.

Up to this point we've used el cheapo batteries so it's not like we're trying to protect $1500 worth of premium AGMs. The el cheapo group 29 Wally World Maxx "DC" battery that was in the RT was 2.5 years old, IIRC, and it was still performing quite well. The previous owner of our Trek had just installed two Interstate group 31 "high cycling" fleet batteries. After about five-six months of boondocking they still seem fairly strong, though I have not run a capacity test on them. I am thinking they will be toast or at least compromised sooner rather than later as they are not designed for RV cycling use.

[Urlauber]

Originally Posted by SteveJ

For the low $$ it works fine with our two group 31 FLA batteries, I think.

https://smile.amazon.com/AiLi-Voltme...s%2C178&sr=8-3

Steve, I have a similar situation with two Group 31 AGM batteries - can you describe how/where you installed the shunt? Perhaps have a picture?

Also, for our purposes, would a 100A or 350A shunt be better? I can't see it ever going over 100A but what do I know... better safe than sorry?

[SteveJ]

Originally Posted by Urlauber

Steve, I have a similar situation with two Group 31 AGM batteries - can you describe how/where you installed the shunt? Perhaps have a picture?

Also, for our purposes, would a 100A or 350A shunt be better? I can't see it ever going over 100A but what do I know... better safe than sorry?

The shunt is installed on the Neg feed from the batteries. All current must flow through the shunt. It needs to be protected from the elements. I put ours in a small plastic deli tub from the grocery store.

Definitely go with the 350, especially if you start a genny off of your batteries or power a medium or bigger inverter. I think the price spread is only $5-8. The 350 is rated for a 500 amp surge.

[avanti]

Originally Posted by SteveJ

Definitely go with the 350, especially if you start a genny off of your batteries or power a medium or bigger inverter. I think the price spread is only $5-8. The 350 is rated for a 500 amp surge.

Although I agree with this advice in the described case, it should be understood that the difference isn't just money. Picking a larger ampacity shunt trades precision for capacity. For this reason, one shouldn't use a larger shunt than the situation requires.

P.S. -- note that shunts are supposed to be derated from their published specs for continuous use. IIRC, the rule-of-thumb is to derate by 1/3.

[booster]

Originally Posted by avanti

Although I agree with this advice in the described case, it should be understood that the difference isn't just money. Picking a larger ampacity shunt trades precision for capacity. For this reason, one shouldn't use a larger shunt than the situation requires.

P.S. -- note that shunts are supposed to be derated from their published specs for continuous use. IIRC, the rule-of-thumb is to derate by 1/3.

Absolutely true and especially the derating. More than 1/3 may even be needed if you put it in a box or in a hot area with poor ventilation.

[Urlauber]

I have sort of abandoned the idea of adding a SOC monitor.
I like simple, and looking at voltage is simple. 12V - battery almost empty ... 13V - battery almost full. Maybe I don't care about the exact Whrs in and out, and just want to know if I need to crank up the genny or not.

Generally, the solar panel produces enough electricity to keep the fridge and some other stuff running (in full Sun, in Summer). The solar charger thing shows voltage usually about .2V higher than what the battery reads.

One thing I noticed, didn't expect, but kinda like - the coach and chassis batteries usually show the same voltage, and if one is different than the other they usually balance out (up or down) quickly. Not sure if this is by design or what, but this way I just have to keep a close eye on the house battery and the starter batt will be ok.

[engnrsrule]

The battery monitoring is helpful to me because as a frequent Boondocker, the Victron tells me not only the voltage and SOC (as a percentage), but a predictive battery longevity, based on the loads experienced. This can alert me if i have more things on than I need or if someing is drawing more than expected, and thereby help manage loads.