A summary

[AJMike]

Originally Posted by Winterbagoal

It's not an issue or a problem that you need to worry about.

I worry about a lot, but this is not one of those things I am worried about. I assume that the various devices are designed to work properly when several of them are active. It is only something that I am curious about. I used to teach math and computer science and I guess I am just a curious person with a lot of odd questions.

If there are 2 simultaneously active inputs to the batteries, do both of them apply charge? Or only one at a time? Since our current AGM batteries charge quickly when we are on the road I assume that the alternator charge is being applied regardless of whether or not the solar is also being applied, but I just wondered if both were applied separately.

[DavidM]

The question of multiple charging sources with each having different voltage setpoints is a complicated one and depends on the battery, the current being charged and how the battery responds.

First all charging sources will coexist fine but at what charging rates?

So lets assume that you have a solar system that can put out 20 amps and it is set at 13.0 volts. And you have a converter that can put out 45 amps and it is set at 14.0 volts. For sake of this discussion assume 200 Ahs of FLAs that were at 50% SOC when you start.

In that starting condition when you apply 65 combined amps the batteries will probably be below 13.0 volts, at least at first because both sources are supplying their maximum but the internal impedence of the batteries is low so the voltage stays below 13.0.

Then after a while, say as the batteries reach 70% SOC they reach 13.0+ volts. Then the solar panel controller will cut out. Actually that isn't quite what happens, the controller throttles back and the voltage drops because the battery isn't seeing the same current as before, but when the voltage drops the current goes back up, etc, etc. A happy medium is established where the solar controller's output is reduced, the converter is still putting out full current and the battery keeps charging.

Not too long afterward the solar controller is completely off because the voltage even without its current is above its set point. Then the converter is the only one putting out any current and the voltage continues to rise. At some point, probably 85-90% the converter reaches its set point and it begins throttling back but the same thing happens as it finds its happy medium but at reduced current. The battery keeps charging as its resting voltage is 12.7 but it is charging at a lower rate until the converter finally cuts off and switches to float.

LPO batteries have much lower internal impedence but I suspect the process is much the same but the solar panel starts reducing current much later, probably at about 95% SOC.

Whew!!! Too many words, I know.

David

[AJMike]

Originally Posted by DavidM

Whew!!! Too many words, I know.

No. Not at all. You needed to write a lot to explain a complicated process, and it all made perfect sense.

Thanks for clearing that up.

[Coachz]

Not scientific at all but before all the lock down, I upgraded to 4 Battleborn batteries, a Sterling dc/dc 60 amp charger. We picked up the unit and the battery bank was at 91%. (they demonstrated using the Air conditioner on the system which used about 1% per minute of use). Looking at the Victron app when I was stopped at a light after about 25 minutes of driving, my battery bank was back up to 100%. So my rudimentary math says 400AH x .91 = 364 400-364 = 36AH charged in about 25-30 minutes.

[DavidM]

Your math is ok, but aren't you relying on two imprecise readings of SOC, taking the small difference to calculate amp hours charged. A 5% real difference would halve or increase by 50% the amp hours.

At least use the same device on both before and after to measure state of charge.

David

[Coachz]

Originally Posted by DavidM

Your math is ok, but aren't you relying on two imprecise readings of SOC, taking the small difference to calculate amp hours charged. A 5% real difference would halve or increase by 50% the amp hours.

At least use the same device on both before and after to measure state of charge.

David

The victron app was what I was looking at both during the demonstration and when I checked after 25 minutes.
I don't understand the "A 5% real difference would halve or increase by 50% the amp hours." part. I am a noob.

[DavidM]

OK using the same device before and after I can buy your conclusions.

36 amp hours added in 25-30 minutes is great, particularly at 90+% SOC when conventional batteries would slow way down charging. Do you know what voltage the Sterling was putting out during that period. Also what chassis were you driving?

Next time you are out and the batteries are down that low or lower, stop and feel the alternator case after 30 minutes at that charging rate. I suspect it was real hot.

David

[Coachz]

Ford E450 chassis.
http://www.sterling-power-usa.com/li...2120manual.pdf based on type of battery, you need to set it differently.

[AJMike]

Originally Posted by DavidM

Next time you are out and the batteries are down that low or lower, stop and feel the alternator case after 30 minutes at that charging rate. I suspect it was real hot.

It has been my experience that after 30 minutes of driving everything in the engine compartment is hot and I would never suggest putting your hand on an engine component after 30 minutes driving, even in the Winter.

Just my opinion.

[AJMike]

Originally Posted by Coachz

Ford E450 chassis.
http://www.sterling-power-usa.com/li...2120manual.pdf based on type of battery, you need to set it differently.

That is very interesting as it is not the Sterling DC-DC charger that Battle Born suggested that I use with their batteries. The one they suggested is here:

https://battlebornbatteries.com/shop...-dc-converter/

Just out of curiosity (as I have been trying to figure out which DC-DC charger to use) what was the cost of the one you used?

[DavidM]

Yes underhood temps are hot. But alternators get hotter. A high output alternator for marine use made by Balmar and others gets up to 200+ F case temperature. Their external regulator has a probe that cuts back amperage when the temp hits 180. That temp will burn your finger as soon as you touch it. I think that they specify 220F as the maxumum alternator case temp.

I have used Balmar alternators a lot on boats. Their smallish alternator is rated at 100 amps and feeding 4 GC batteries that were down to 50% will trigger the high temperature cutback and reduce amperage in half to keep the temp down below about 200.

I am concerned that any chassis alternator can overheat if pushed like the Sterling and other B2B chargers do. I think that is why Mercedes recommends no more that 40 amps be drawn from their alternator for external loads. And realize that these modern engines have significant internal loads to run everything unlike a mechanical diesel engine on a boat which requires no power to keep running.

The 70 or so amps that Coachz measured is more than I would expect the alternator to handle for long without deterioration.

David

[Coachz]

Originally Posted by AJMike

That is very interesting as it is not the Sterling DC-DC charger that Battle Born suggested that I use with their batteries. The one they suggested is here:

https://battlebornbatteries.com/shop...-dc-converter/

Just out of curiosity (as I have been trying to figure out which DC-DC charger to use) what was the cost of the one you used?

from my installer quote:

Battery to Battery Charging Kit, 25ft, 60A, Sterling / Standard Battery to Battery Charging Kit, 25ft, 60A, Sterling / Standard Alternator charging kit enables battery to battery charging of the house battery from the alternator. Scope: -
Sterling ST-BBW1260 12V, 60A, waterproof battery to battery charger 25ft of 4ga wire, lugs and heat shrink 60A breaker
$ 422.24

[AJMike]

Before I ordered the DC-DC charger I bought I spoke with the tech at BB and he said that as far as he was concerned the "sweet spot" (his term, not mine) for charging BB Lithium batteries was 40-45 amps. I thought about the Sterling 60 amp charger and the Renogy 60 amp charger but ended up buying the Renogy 40 amp version instead. It will take longer to charge but perhaps the lower amperage will cause me less trouble.

I also noticed that Victron, which also makes DC-DC chargers, tops theirs off at 30 amps. I have already bought the Renogy 40 amp but it does not seem to have ever left the Amazon warehouse according to the tracking information and if it does not arrive this weekend I will cancel the order and get the 30 amp Victron instead. It is more expensive but probably better technology and bluetooth enabled.

[AJMike]

Originally Posted by Coachz

from my installer quote:

Battery to Battery Charging Kit, 25ft, 60A, Sterling / Standard Battery to Battery Charging Kit, 25ft, 60A, Sterling / Standard Alternator charging kit enables battery to battery charging of the house battery from the alternator. Scope: -
Sterling ST-BBW1260 12V, 60A, waterproof battery to battery charger 25ft of 4ga wire, lugs and heat shrink 60A breaker
$ 422.24

Here is the unit that BB sales sent me as an official quote.

https://battlebornbatteries.com/shop...-dc-converter/

It is different from what the tech himself suggested in output and different entirely from what you were quoted. The odd thing is that yours is listed as a charger and the one above is listed as a charger on the BB webpage but referred to as a converter on the Sterling web page.

https://www.sterling-power-usa.com/S...rycharger.aspx

In any case it is not what I ordered so I guess the issue is moot.

[Coachz]

Originally Posted by Coachz

from my installer quote:

Battery to Battery Charging Kit, 25ft, 60A, Sterling / Standard Battery to Battery Charging Kit, 25ft, 60A, Sterling / Standard Alternator charging kit enables battery to battery charging of the house battery from the alternator. Scope: -
Sterling ST-BBW1260 12V, 60A, waterproof battery to battery charger 25ft of 4ga wire, lugs and heat shrink 60A breaker
$ 422.24

link I found:
https://battlebornbatteries.com/ster...ttery-charger/

[AJMike]

Originally Posted by Coachz

link I found:
https://battlebornbatteries.com/ster...ttery-charger/

That is the 30 amp model. After reading some of the posts in this thread I think that 30 amps may be much better than 60 amps even though it means slower charging.

[Coachz]

Originally Posted by AJMike

That is the 30 amp model. After reading some of the posts in this thread I think that 30 amps may be much better than 60 amps even though it means slower charging.

from: https://battlebornbatteries.com/shop...erter/#reviews


Sterling Power Battery to Battery Charger 12V input to 12V output up to 60amps. DC to DC converter
Rated 5.00 out of 5 based on 2customer ratings(2 customer reviews)
$408.00

Now you can smart charge the housebank in your Tow Camper, Boat in tow, or Sprinter Van while driving down the road.

DC Powered Smart Charger, perfect for smart charging your auxillary battery bank in a Mercedes Sprinter or Ford Transit van, Doesnt have the limitations of a tradional relay.

It correctly calculates the charging needs of the house bank and smart charges anytime the boat or van is started and goes into float voltage when the battery is full.

Choose from 9 preset output charge profiles, or set your own w/ a user customizable profile. Loaded with features, optional remote displays available, please check out our website for additional information.

Part # BB1260 has a 12v input at up to 60 amps and output is 12v at up to 60 amps.

Simply connect in between a starting battery and house bank and any time the vehicle’s alternator is running this smart charger will smart charge the output bank.

[moabdds]

Originally Posted by AJMike

Just to add some confusion to the mix -

One of the local shops that BB recommended to do the install send me an estimate for all the work. Part of that was the installation of something they called a BIM - battery isolation manager - which seems to be this item:

https://battlebornbatteries.com/shop...ation-manager/

The item number (BIM-225) matches the number on the BB page and this shop is a BB recommended installer, so I am pretty sure this is the item.

The shop says that they will install anything I want, from any manufacturer, but that they have been installing this for a very long time as part of their lithium battery upgrades and have never (they were very clear they meant never) had a customer report an issue.

The thing is that this item is about $180 and the shop, which charges for pretty much everything they do, does not charge for the installation of this BIM which implies to me that it takes no real work. The DC-DC charger costs $400 and the installation estimate for it was 2 hours.

Given all of that I have to ask if the DC-DC charger is recommended because it is better or because it generates more profit. I don't know. Theoretically I would think the charger is better because it serves both to provide a steady constant current and isolates the alternator from spikes while the BIM only connects and disconnects the alternator from the battery at set time intervals. Surely the DC-DC charger is better from an engineering point of view, but is it really better from a practical point of view.

If no one has ever complained about issues with the less expensive model then I assume it does what it was designed to do, and at lower cost. Of course there is also the issue of how long the alternator will take to fully charge the batteries - the BIM switches on and off, 15 minutes on and 20 minutes off so the batteries are only getting charged about 43% of the time - but I am not sure that it matters much during a 5 or 6 hour drive.

I installed the Battle Born BIM in my Itasca 27N. It was located behind the 12v breaker panel, which in my coach, is located on the driver's side near the front. Getting access to the OEM BIM to change it out was a royal PITA. I also had to do some alterations to make it all fit. I installed it in January and it has worked like a charm. I have 3 BB batteries in my bank.
Jon F.