Battery Isolators,Separators, and Switches? - Page 17

Mike Wilson · 11-04-2018, 10:26 AM

Nice stuff and sorry for not getting back as quickly as you did to me. A few questions.
Looks like the vertical axis is all kinds of things, Temperature, Percent of charge, battery voltage, current etc.

How did you determine the state of charge and what battery is it referring to? Normally, I determine this by letting the battery sit with no current in or out at least 4 hours and measure the open circuit voltage.

It would be interesting to monitor the current for each battery to see what is really going on. The data shows that after an initial high current from the alternator, the current drops to about 40 amps... but where is it going and might the starter battery (if it started at 100 %) is now charging the house battery at more than 40 amps?

I did some estimates for voltage drop and came up with similar numbers, about 1 percent. Guessing at 10 feet of 2 Ga. wire to the house battery and another 10 feet of return (frame? wire?) could be about 3.12 milliohms total. At 40 amps I get your number of 125 millvolts drop or about 1%. But that drop shows up at the van battery and changes things.

Lifeline states that the internal resistance of their battery is 2.15 milliohms.
One model is that the alternator is a voltage source that wants to keep the starter battery at some voltage. If we have no resistance in the wires to the house battery, both batteries see the same voltage. The current that flows in each battery is the difference between the alternator voltage and the internal battery voltage divided by the internal resistance.

But I need wires so I stick in 3.12 milliohms of resistance to the house battery and assume the alternator and starter battery stay at the same voltage. Now the current that flows in the house battery is the difference between the alternator voltage and the internal house battery voltage as before but now we divide by the total resistance. This went from 2.15 milliohms to a total of 2.15 milliohms plus 3.12 milliohms or a total of 5.27 milliohms.

So given this model, that 1 percent drop makes a big difference due to the low internal resistance of the battery.

Example: Alternator is at 13.086 volts and the internal house battery is at 13.000 volts and no wires, zero resistance. The current is 86 millivolts divided by the internal resistance of 2.15 milliohms or 40 amps.
Now I stick in my wires and I get 86 millivolts difference but now it gets divided by the total resistance of 5.27 milliohms. Now I only get 16.3 amps.
Still, this is not bad and way better than my stock Sportsmobile back in 2000.

I am not trying to bash this technique. It only points out that you run up against having to throw a lot of copper at the problem to make things better and better.
Years ago (dark ages) in 2000 when I bought my RB50 PSD Sportsmobile, they had skinny wire and in series was a thermal fuse and the charging system was terrible. The thermal fuse would open and close all the time in the desert when it was hot and when you really need to charge the house battery to keep the frig working. I tried several marginal work-arounds. I I was not aware of other systems that worked as well as you have described.
I am sure they work well for most people and most importantly, you can just go out and buy one. Back then, I eventually decided there are other ways rather than trying to push lots of current through "long" wires.

Thanks for sharing your data. If you have numeric data used to make up the graphs, I would like taking a look at it. It is rare that people really take a detailed look at things.

Mike Wilson

Scalf77 · 11-04-2018, 06:33 PM

Mike,
In that scenario the house battery and wires are in parallel to the starting battery and other van loads in the system. Also the battery is just one of the loads, as I still have what ever is drawing power from the house side of things. In my case that can be a Starcool AC system that requires some large amount of power at least when the blower is on high, if I am running my on board computer I add some additional load.

That is where your system, as innovative as it is, would be a problem for me. With only 30 Amps from the charger I wouldn't have much to go into the battery. I certainly understand the negatives of just charging with a straight alternator, but that is not my primary charging method, I use solar when available and plugin at home. It is all good discussion, and there really is no perfect solution that covers all needs (other than a second alternator with a multistage regulator) and even that would be overkill for some set ups.

I measured the current going into the battery with a Pentametric Battery Monitor from Bogart Engineering the same Monitor for the SOC information. I am extremely confident that the current going into the battery was from the alternator. I do a times run into situations when the combined load of charging the battery and running AC that when I am at idle that the alternator can't keep up with the load and the Battery Separator disconnects from the low voltage, and the connects back up when throttled up. I will look to see if I have the raw data, or if I think about it I will try to collect it again. I look forward to further discussions.

-greg

Railvan · 11-11-2018, 09:15 PM

I asked Scalf77 this in a PM but could not get these diagrams to load in the message so I am posting it here as well. Sorry for the double post, Greg.

Would adding a normally open switch in the wire (see green circle location on diagram A) between the Start circuit of the ignition and the Start Assist tab on the 1315 stop the 1315 from making the van battery connect every time I start the van? And would this allow me to manually connect the van battery to the start batteries by flipping the switch to the closed position?

If this will not work, I'll wire up a switch as shown in diagram B.

Thanks,

Brian

Scalf77 · 11-12-2018, 06:22 AM

Yes, that would work to disable and enable the start assist feature.

-greg

allenl · 11-18-2018, 05:36 PM

I just picked up 2 lithium 100ah batteries for my rig on sale for black friday. The additional depth of discharge, weight savings, and cycles convinced me that lithium was worth the added cost.

I'm re-wiring from the original 2000 SMB setup, and trying to decide the best way to keep the house batteries charged (in addition to 200-300 watts of solar). My current plan is to use a battery to battery charger like this: https://redarcelectronics.com/produc...attery_charger.

My main concern being able to keep the start batteries topped up, or having the ability to connect the house bank to the start batteries in a dead-battery situation. Any thoughts on how to add this capability to the system? I was thinking about using a manual battery switch to connect the two when needed.

This is a great thread by the way... I'm still learning lots on these systems.

WanderingBob · 11-18-2018, 11:40 PM

Oh, so much info, but well laid out! Nice

Wandering Bob

Scalf77 · 11-19-2018, 06:56 AM

Quote:

Originally Posted by allenl

I just picked up 2 lithium 100ah batteries for my rig on sale for black friday. The additional depth of discharge, weight savings, and cycles convinced me that lithium was worth the added cost.

I'm re-wiring from the original 2000 SMB setup, and trying to decide the best way to keep the house batteries charged (in addition to 200-300 watts of solar). My current plan is to use a battery to battery charger like this: https://redarcelectronics.com/produc...attery_charger.

My main concern being able to keep the start batteries topped up, or having the ability to connect the house bank to the start batteries in a dead-battery situation. Any thoughts on how to add this capability to the system? I was thinking about using a manual battery switch to connect the two when needed.

This is a great thread by the way... I'm still learning lots on these systems.

I would inquire with Redarc on what their Lithium profile is, they appear to only limit the output voltage. Lithium does not have the same needs as a lead acid battery.

You could put a manual emergency switch or two between the two systems. Care must be done to ensure that the B to B charger is off or out of the circuit when you do, or you could damage B to B.

Lithium Batteries are not really drop in compatible to lead acid batteries.

-greg

allenl · 11-19-2018, 08:25 AM

Quote:

Originally Posted by Scalf77

I would inquire with Redarc on what their Lithium profile is, they appear to only limit the output voltage. Lithium does not have the same needs as a lead acid battery.

You could put a manual emergency switch or two between the two systems. Care must be done to ensure that the B to B charger is off or out of the circuit when you do, or you could damage B to B.

Lithium Batteries are not really drop in compatible to lead acid batteries.

-greg

Thanks for the input, I reached out to Redarc on the charging profile.

Good input also on shutting down the charger prior to combining the two systems.

Mike Wilson · 11-20-2018, 06:01 PM

Not sure what Lithium battery you are buying but from what I see, they have their own Battery Management System built in. The LiFePO4 types do. They just need to have sufficient voltage to provide good Bulk charge and also for float. I have used this type of battery for other applications and do like the way they work.
I do like the charger system you are looking at ... much like what I did about 10+ years ago but I used the discrete Sportsmobile AC charger and a cheap inverter. I think it is the best way to take care of your very expensive batteries.
You may have this figured out already but when AC is available, you will want to have a means of charging. In my system, the built in charger, running off of 120 volts is switched in by means of a relay. Using a dedicated charger would work fine for shore power since all these chargers are just voltage sensing current sources and won't fight each other.
It is not easy to use the house battery as a starter battery. There is a reason the starter battery is so close to the starter. The starter requires a lot of current and the only way to get that is with big fat wires. If you don't have any current draw from the starter battery, like a radio or stuff like that, you might just keep an eye on the voltage and fire up the engine once in a while. I have my electrical system set up so the starter battery gets connected to the house battery only when I have shore power. Otherwise, they are separate but I do have a button I can push to see how the starter battery is doing. No perfect solution to keep house and engine battery up all the time.
Looks like it will be a very nice electrical system and solar too.

Mike Wilson

moorefc · 11-21-2018, 08:32 AM

Quote:

Originally Posted by allenl

I just picked up 2 lithium 100ah batteries for my rig on sale for black friday. The additional depth of discharge, weight savings, and cycles convinced me that lithium was worth the added cost.

I'm re-wiring from the original 2000 SMB setup, and trying to decide the best way to keep the house batteries charged (in addition to 200-300 watts of solar). My current plan is to use a battery to battery charger like this: https://redarcelectronics.com/produc...attery_charger.

My main concern being able to keep the start batteries topped up, or having the ability to connect the house bank to the start batteries in a dead-battery situation. Any thoughts on how to add this capability to the system? I was thinking about using a manual battery switch to connect the two when needed.

This is a great thread by the way... I'm still learning lots on these systems.

Since you spent a lot on these batts, assuming Li-Ion, you might want to read thru this on extending their life....https://batteryuniversity.com/index...._ion_batteries
Note the cycle life and ways to extend/shorten that....