Going from 1 House Battery to 3

[Spicoli]

I am preparing to order 2 new house batteries identical to my 4 month old (newish) house 100Ah battery. I finally found a location in my 20' Class B RV where I can put the 2 new ones so they are within 2 or 3 feet (of wire) from the existing house battery (yay!)

QUESTION: What impact will the 3 house batteries have on my Ford E-350's alternator? and on my 55 Amp Powermax 110VAC to 12VDC Converter/Charger? (which only operates when plugged into shore power or the generator is on)

I can't imagine I have to do anything with them to accommodate the 3 total 100Ah batteries. Right?
.

 

[ckelly78z]

3 batteries are just more capacity than 1, not more draw on the alternator.

 

[B and C]

I didn't do anything on mine for my 350Ah set.

 

[bass_sears]

What kind of batteries are you adding?

Only issues I've heard of are lithium batteries due to their ability to accept current much more quickly than a lead acid battery, basically burning out your alternator because it's running at max output for too long... solution for that is usually a DC-DC charger.

If you're going with lead acid you should be fine.

-- Bass

 

[Spicoli]

What kind of batteries are you adding?

Only issues I've heard of are lithium batteries due to their ability to accept current much more quickly than a lead acid battery, basically burning out your alternator because it's running at max output for too long... solution for that is usually a DC-DC charger.

If you're going with lead acid you should be fine.

-- Bass

Sealed Lead Acid (Mighty Max Battery ML100-12 SGM 100AH)

 

[Elbear1]

Why waste money on lead batteries? You can replace the 1 you have with a lifepo4 and get the equivalent of 3 for 1/3 weight and space.

US $603.84 26%OFF | KLUOSI 8PCS 3.2V 120Ah LiFePO4 Long LifeCycles 3500 Times Max 3C For Solar Energy Storage Battery pack E-Bike battery
https://s.click.aliexpress.com/e/Lo3NvQli

 

[highdesertranger]

Spicoli I posted in your other thread those ARE NOT 100Ah batteries. in fact you would be lucky to get 100Ah's out of all three of them. highdesertranger

 

[Spicoli]

Why waste money on lead batteries? You can replace the 1 you have with a lifepo4 and get the equivalent of 3 for 1/3 weight and space.

US $603.84  26%OFF | KLUOSI 8PCS 3.2V 120Ah LiFePO4 Long LifeCycles 3500 Times Max 3C For Solar Energy Storage Battery pack E-Bike battery
https://s.click.aliexpress.com/e/Lo3NvQli

I was not aware I could replace 3 100 Ah SLA with 1 - 120Ah  [font=Tahoma, Verdana, Arial, sans-serif]lifepo4. BTW they show as $743 today. Typically they are around $900 aren't they?[/font]

 

[Spicoli]

Spicoli I posted in your other thread those ARE NOT 100Ah batteries.  in fact you would be lucky to get 100Ah's out of all three of them.  highdesertranger

So the discharge curve for it is not correct?
 

 

[Spicoli]

I guess another question is: should I run my own discharge test? I recently put in a shunt and battery discharge meter.

 

[Elbear1]

I was not aware I could replace 3 100 Ah SLA with 1 - 120Ah  [font=Tahoma, Verdana, Arial, sans-serif]lifepo4. BTW they show as $743 today. Typically they are around $900 aren't they?[/font]

Thats 240ah. Look around aliexpress. BLS is a known vendor. Used Valance 138ah $500 on amazon. Shunbin 200ah on amazon $800

 

[highdesertranger]

the curve might be right but look at the hours. the recognized standard for measuring Ah is the 20 hour rate. I don't even understand what they are trying to show on that chart. it surely doesn't show a 100Ah battery. in the reviews the buyers that tested it reported around a 35Ah battery. highdesertranger

 

[wayne49]

Renogy also uses the 10 hour rate. Not saying that 10 is better, just odd, since the majority of batteries, that I have looked at, used 20.
Difficult to make comparisons. Maybe that is the motivation.

 

[Spicoli]

I am not concerned about 1 bad review at Amazon where a random person claims it's 35Ah without providing any detail. Besides a few other bad reviews (that the battery failed too early) everyone else is very happy with it. I have been too. Also note it also has a 1 year warranty. I used it on an 8,000 mile trip over 6 weeks and I was quite impressed with it's capacity.

Anyway. Did some learning. Measuring a battery over 10 or 20 hours is fine and will not damage it (as pointed out earlier even Renogy reflects the 10 hour test). It's simply a measure of power dissipated over time showing the drop in terminal voltage as that time passes while current is held steady. Whether you do that in 5, 10 or 20 hours is fine and should not hurt it if you don't let terminal voltage drop below 50%. So the higher the discharge current the lower terminal voltage ... if you drop the terminal voltage too low by allowing a higher discharge current you can greatly reduce the life of the battery and/or even damage it. So always bear that in mind. But the 9 Amps used in the 10 hour test is fine (that's a fairly normal load).

I already have a 100 amp shunt and digital discharge multi-meter attached to my house battery so I can run my own power test. All I have to do is reset my digital multi-meter, properly 3-stage charge the battery to 100% (until float is reached), disconnect battery from everything for about 30 minutes to let it settle, connect a stable resistive load (like a few light bulbs) to draw 5 to 10 amps, and then let it run for X hours to let my digital multi-meter collect the total power dissipated to generate a reading when it reaches the 50% voltage level (then stop the test so I do not damage the battery and/or reduce its life). Then extrapolate that power reading (multiply by 2) to get total battery capacity.

The RV is in storage right now but hopefully I will get a chance to do this after the Christmas holidays.

 

[Spicoli]

... I don't even understand what they are trying to show on that chart.  it surely doesn't show a 100Ah battery ...

Sure it does. The 10 hour curve reflects roughly 90 Ah total capacity (TC) at 50% discharge level. Why is it below 100 AH? Well I did me some learnin' LOL. The curves below shows progressively higher discharge rates (thus lower terminal voltages) going left and thus reflects a lower total battery capacity value in each curve as you move to the left. If you calculate TC as you move right to left you see 90 Ah, 85 Ah, 68 Ah, 27 Ah, 18 Ah, not sure about the 180 Amp curve LOL).

So. Based on the behaviors in the chart we can see that the 20 hour chart (going to the right of the 9 Amp curve) will certainly show less current draw, and higher terminal voltages thus moving the total capacity more toward 100 Ah (could even exceed 100 Ah).

It will be interesting when I run my own test. I will try to apply a current load that makes my 50% discharge rate last close to 20 hours so that I have the best chance to hit the 100 Ah capacity

 

[highdesertranger]

what's amazing to me is two people can look at the same graph and see two totally different results. to me it appears they fudged the numbers.

for instance why isn't the 60 on the time side right where it changes from minutes to hours. last time I checked 60 minutes = 1 hour. to me it appears they moved the 60 to the left.

then on the voltage side what do those lines stand for. they marked the 12v and the 9.6 volt but what about the other lines? if you ask me those lines should represent 2v each where they put 9.6 should be 4v and where 90A crosses 10v is at a little less than 20 minutes.

so I just don't see it. all I see on that graph is deception. but I am all for you testing your battery and posting the results here.

highdesertranger

 

[Spicoli]

This is not a Mighty Max chart. It is an industry standard discharge 'battery behavior curve' for commonly available AGM Lead Acid batteries (like mine or Renogy's or Windy Nation's). The chart is not meant to be deceptive. It is meant to show the behavior for common SLA/AGM batteries. Mighty Max includes this chart with their battery spec (I assume) because they have tested it and they found it behaves like this common chart reflects.

The 60 is not where you want it because the program that made the chart bumped it over to the left because of the 'tick' where minutes switch to hours LOL. Trust me - the 60 belongs where you desire it and you should base your calculations on it being there.

The voltage lines on the left axis are non-linear and nothing really matters there on that axis except the 12 V line because that is where 'all eyes are' when you hit the 50% discharge mark. Note that different manufacturers have different 50% discharge points (some say 12V, some 12.3V, some say 12.5V, etc.). That spot (and its corresponding time) is of major concern. Mighty Max told me to use 12.2 V.

If you do not know how to interpret the discharge graph here's how to read the chart and calculate total battery capacity. You can do it like I did for each of the 6 curves except you can't for the 180 A curve b/c the battery immediately drops below the 50% discharge rate LOL. Anyway - here's how you calculate Total Battery Capacity using the 9 A curve: Follow the current curve for the 9.0 Amp discharge rate to where it crosses the 50% discharge voltage point and observe that point in Time (roughly 5 hours). So you then multiply the (roughly) 5 hours times 9.0 Amps and to get 45 Amp hours (Ah). Since that is the 50% discharged point you have to multiply it by a factor of 2 to get Total Battery Capacity (90 Ah).

Don't forget - you would never want to apply a high current like 90 amps or higher to your battery since you would immediately damage it!

 

[highdesertranger]

ok, whatever you say. I am done. highdesertranger