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Old 11-13-2018, 11:55 AM   #11
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I just noticed on the website for the batteries that Hymer is shown as one of the two sales affiliates in Germany. One other in Europe and the rest in less developed areas.
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Old 11-13-2018, 02:03 PM   #12
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It looks like they are also partnering with Victron, which should be able to give them near instant market penetration if Victron starts to sell/push their systems.


https://www.bos-ag.com/news/news-archive
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Old 11-13-2018, 07:35 PM   #13
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The Hymer connection likely now means a Thor connection.

https://www.bos-ag.com/news/news-arc...-2018-gewonnen

Description of Hymer system: https://www.hymer.com/en/models/tech...ry-system.html

It's not the 4 to 1 ratio, it can be more lithium than lead so I guess it is very flexible.


Harry's 1 to 1 ratio likely offers great price/performance particularly at around 100Ah AGM & 100Ah LFP. There would be no problem running a microwave oven for example.
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Old 11-13-2018, 10:09 PM   #14
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It is interesting on both the manufacturer and Hymer explanations they talk about priority charging (as in first) for the AGM so it is sure to get fully charged. In a some ways that seems a bit contrary to being able to get the most benefit from the system. The bos-ag site does state another place that the lithium will be used to charge the lithium so a bit of contradiction there.



They say all the timing of charging is built in to the control system, but I would think that would be probably not be all that needed. The AGMs are essentially always be at lower voltage the lithiums are, so they will get charge when the lithium won't, unless the charger has enough capacity to get to a high enough voltage by satisfying the acceptance of the AGMs first until they get to the lithium voltage. At that point the AGMs wouldn't be full, though. They could delay turning on the lithium charging until a higher voltage is seen on the AGMs, perhaps at 14.3v which would be at the end of the bulk stage, but that is going to extend the charging time quite a bit before the lithiums charge. I guess I would think you would want to get charge into the lithium batteries if you want to cycle off them as they mention. Especially with solar, they could wind up cycling in the mid range of the AGMs all the time and never get them full enough to charge the lithiums.


It seems like it would make more sense to charge the high acceptance lithium batteries first and then cycle of that and use them to charge the AGMs. The lithium should get a bit more out of the solar and also shore charging if the charger is fairly large, in any given amount of time. The difference would probably be even more if on the van alternator or standalone generator where you really want to minimize charge/run time like Harry does.


It is going to be very interesting to see how it actually functions in the real world, and especially if Victron starts putting out systems or AGM enhancement systems.
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Old 11-14-2018, 12:02 PM   #15
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The AGM would want to be at a lower voltage but if the AGM and LFP are connected via the same bus then both will be at the same voltage. Keeping them connected seems safer to me - no potentially damaging huge current outflow or inrush on/with the AGM.

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..............................
It seems like it would make more sense to charge the high acceptance lithium batteries first and then cycle of that and use them to charge the AGMs. The lithium should get a bit more out of the solar and also shore charging if the charger is fairly large, in any given amount of time. The difference would probably be even more if on the van alternator or standalone generator where you really want to minimize charge/run time like Harry does...................
That's what I think too.

It would seem to be an unnecessary complication to try to charge the AGM first. The AGM will be charging (float or otherwise) maybe 90% of the time (when connected to the LFP battery). Could that be what they mean by priority to the AGM?
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Old 11-14-2018, 12:39 PM   #16
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The lithium keeping the AGM at float, albeit probably a fairly high float voltage, is another interesting thing in that they say the priority discharge the lithium first. This could put the lithium into low voltage shutdown before the AGM would start to discharge at about 12.8v. If this is what happening, the priority is happening all by itself so no control of it really needed by the BMS.


If the AGM was discharged far enough and the charger not particularly large so it couldn't get the charge voltage up very quickly, the AGM would also charge first to some point determined by the acceptance of the AGM vs charger size vs what voltage the lithium comes out of low voltage shutdown.


Personally, I would like to see pretty big charger on a system like this for shore power and engine generator. Probably sized so that you wouldn't hurt the AGMs by too fast charging if they were low, so something in the .4C of the AGM. That would give you a 120 amp charger for the theoretical 300ah of AGM/100ah of lithium system. The large output would allow the charger to reach the turn on voltage of the lithium quickly for faster recovery. That leaves the solar, that would probably never charge the lithium until the AGM was near full and the voltage finally came up. This may be the priority charging they are talking about, which also will happen all by itself with no active BMS actions required.


It appears they may be making it look like their BMS is doing all kinds of charge allocating, when it is really just the way it happens based on the size of AGM bank and chargers, and the wake up voltage of the lithium pack. Nothing wrong with doing it that way, as it is cheap, effective and reliable, but a bit of a marketing fib if that is what is happening. I am sure they wouldn't want to tell potential buyers about all the things that may affect the results they actually get.


If I were to get a system like that, it would have two battery monitors on it before it ever got powered up
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Old 11-14-2018, 01:56 PM   #17
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With a parallel LFP AGM setup I think you could run the lithium from 90% SOC OCV down to 10% SOC under moderate load. That looks like it would be from about 13.4V down to just above 12.0V. The AGM could handle that. Right sizing the capacity of the combo bank so that those deep discharges aren't occurring all the time would be good.

On a 300AGM/100LFP or even 400AGM/LFP combo bank exit absorb amps could be set as low as 5A at 14.4V if no loads present or maybe as high as 8A.

I agree about using a big charger. I think I'd size it so that it is not running at 100% rated output. And yes to monitoring it all to know what is going on.
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Old 11-14-2018, 03:11 PM   #18
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The simplest LFP add for me would be to my current two 6-volt lead acid bank at 225 Ah. So I would be at 225LA/100LFP ratio. If LFP costs came way down I might consider going to 200 Ah LFP. I see a higher ratio is recommended (4/1). What is the problem with a lower ratio: 2/1 or even 1/1?
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Old 11-14-2018, 03:43 PM   #19
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Quote:
Originally Posted by markopolo View Post
With a parallel LFP AGM setup I think you could run the lithium from 90% SOC OCV down to 10% SOC under moderate load. That looks like it would be from about 13.4V down to just above 12.0V. The AGM could handle that. Right sizing the capacity of the combo bank so that those deep discharges aren't occurring all the time would be good.

On a 300AGM/100LFP or even 400AGM/LFP combo bank exit absorb amps could be set as low as 5A at 14.4V if no loads present or maybe as high as 8A.

I agree about using a big charger. I think I'd size it so that it is not running at 100% rated output. And yes to monitoring it all to know what is going on.

I did a quick look and couldn't find a decent discharge curve for the Lifepo4 batteries. Do you happen to have one? We know the charge curve has a steep dogleg at the finish end, so it would be interesting to see what the lower end of the discharge curve looked like, as that would be the determining factor in how each of the battery styles got charge as the cycle progressed. If the acceptance voltage for the lithium doglegs up quickly it could get above the AGM acceptance so most or all the charge would be going to the AGM. Superimposing the charge and discharge curves for the two types would be very interesting, especially when charger size gets thrown in.
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Old 11-14-2018, 03:45 PM   #20
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Quote:
Originally Posted by peteco View Post
The simplest LFP add for me would be to my current two 6-volt lead acid bank at 225 Ah. So I would be at 225LA/100LFP ratio. If LFP costs came way down I might consider going to 200 Ah LFP. I see a higher ratio is recommended (4/1). What is the problem with a lower ratio: 2/1 or even 1/1?

Harry is happy, and I think he is at 1 to 1 now on his setup. I don't think ratio if much of a big deal unless it got to be more than the 4 to 1. That 25% of capacity in the lithium would be just about enough to top off the AGM bank if a fast charge brought it up to the bulk/absorption transition, so I think that would be an important element to keep.
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