60a DC-DC Charger only pulling about 40a

Posplayr

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My guess, because the input volts to the B2B are low due to volt drops, the unit is having to work hard ( the currents on the input side may be well in excess of 80 amps) and is reaching protective thermal limit, thus causing automatic reduction of power conversion and a lowered output current
This is quite common and can be seen in other B2B units from Sterling and Victron.

A further consideration is that you maybe overloading the alternator and/or the cables from alternator to starter battery and dropping volts along that path.

Mike
Renogy recommends the DC-DC input side be sized for 50% excess of the output current. According to my calculation ()IIRC) a 3% voltage drop at 16 ft is about a minimum DC-DC input voltage of 12V at 14.5 alternators. I used a 40A but the voltage drop and currents will be proportionate for a 60Amp DC-DC. Any more drop than that will be exceeding 90 Amps in the case of a 60A DC-DC.

 

moonlitsouls

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Renogy recommends the DC-DC input side be sized for 50% excess of the output current. According to my calculation ()IIRC) a 3% voltage drop at 16 ft is about a minimum DC-DC input voltage of 12V at 14.5 alternators. I used a 40A but the voltage drop and currents will be proportionate for a 60Amp DC-DC. Any more drop than that will be exceeding 90 Amps in the case of a 60A DC-DC.

The last few times i ran the truck and the dc-dc charger i saw anywhere from 40-55 amps , i think it was reducing in some cases when i was driving in the sun and the solar was producing as well , do you know how the dc-dc charger works when it sees other inputs of charge coming into the battery ? i thought they would be completely separate sources , if im putting 20amps of solar , then i should see 60+ amps to the bms ( i use that to monitor charge current)

I think its a voltage issue , when the mppt is charging at full sun , i notice the voltage increase above the actual bms , maybe the dc-dc then reduces its input based on that , i have no idea

at this point , my battery is almost always full , ill take the 40amps and its fine
 
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Posplayr

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The last few times i ran the truck and the dc-dc charger i saw anywhere from 40-55 amps , i think it was reducing in some cases when i was driving in the sun and the solar was producing as well , do you know how the dc-dc charger works when it sees other inputs of charge coming into the battery ? i thought they would be completely separate sources , if im putting 20amps of solar , then i should see 60+ amps to the bms ( i use that to monitor charge current)

I think its a voltage issue , when the mppt is charging at full sun , i notice the voltage increase above the actual bms , maybe the dc-dc then reduces its input based on that , i have no idea

at this point , my battery is almost always full , ill take the 40amps and its fine
Amps where? The DC to DC adjusts current/voltage at the output to obtain the specific Battery voltage profile.

For example, if you want 14.5V out @40Amps (to the Haus battery) but there is only 12V available at the input to the DC-DC the the input current to DC to DC (i.e. the output current from the car battery/alternator ) will jack up (14.5/12.0)/0.8*40 = 1.46*40 Amps = 58 Amps

The DC to DC will boost from 8V (12V is conservative) so it can climb way higher if you are doing this idling.

note the 0.8 factor is assuming 80% efficiency of the DC to DC.
 

Bud Martin

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The batteries (Load) pulls current from the power source (charger), it can only pull up to what the source can supply, and as the batteries getting full, the current draw from the source will be less.
 

Posplayr

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The batteries (Load) pulls current from the power source (charger), it can only pull up to what the source can supply, and as the batteries getting full, the current draw from the source will be less.
The Dc to DC chargers are Buck-Boost and they will step up the output voltage above the input voltage and so they will increase the inport current over the output current.

Look at the input voltage specification of the DC to DC to confirm. It drops to 8v while delivering 14V that is a sure sign!

 

Bud Martin

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It does not matter if it is buck, boost topology, the Load will pull current it needs from the source.
For example, if the load is trying to pull 10A at 14V which will be 140W of power output, so if the source Voltage is only 8V, the INPUT current to the charger will be 140W/8V = 17.5A (for easy math, the conversion loss is not factor in), so if the load pulls less current then input current will drop.

moonlitsouls is talking about the charging current he is observing.​

 

Posplayr

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It does not matter if it is buck, boost topology, the Load will pull current it needs from the source.
For example, if the load is trying to pull 10A at 14V which will be 140W of power output, so if the source Voltage is only 8V, the INPUT current to the charger will be 140W/8V = 17.5A (for easy math, the conversion loss is not factor in), so if the load pulls less current then input current will drop.

moonlitsouls is talking about the charging current he is observing.​

Bud,
Not sure what your point is. You repeated the same example but peppered your post with provably false statements and on top of that feel compelled to interpret moolitsouls post for me?. I could tell you what I think your point is but you probably would not like that.
 

Bud Martin

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Bud,
Not sure what your point is. You repeated the same example but peppered your post with provably false statements and on top of that feel compelled to interpret moolitsouls post for me?. I could tell you what I think your point is but you probably would not like that.
OP: The last few times i ran the truck and the dc-dc charger i saw anywhere from 40-55 amps , i think it was reducing in some cases when i was driving in the sun and the solar was producing as well , do you know how the dc-dc charger works when it sees other inputs of charge coming into the battery ? i thought they would be completely separate sources , if im putting 20amps of solar , then i should see 60+ amps to the bms ( i use that to monitor charge current)

Well, he is not going to see 60A if the batteries are full is he? Why would the batteries be drawing lots of current if it is fully charged?

" false statements and on top of that" What would that be? Please clarify.
BTW, I do know what Buck and Boost converters are, I use the topology extensively in my products design.
 
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Short_Shot

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Bud,
Not sure what your point is. You repeated the same example but peppered your post with provably false statements and on top of that feel compelled to interpret moolitsouls post for me?. I could tell you what I think your point is but you probably would not like that.
You're not understanding the topic.

The statement was that the current from the DC to DC charger varied and the assumption was that the solar output had something to do with *reducing* it as solar output increased.

The explanation is that the current is in fact limited by state of charge, not the solar.
 

Bud Martin

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"The explanation is that the current is in fact limited by state of charge, not the solar." That is what I am trying to explain! as the batteries get full it will draw less current from the source. The source does not force current to the load, the load draws current from the source.
May be I need to improve my English language, it is not my fist language.
 
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Bud Martin

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I would never have suspected.
I am still learning! It is real confusing for me lots of time because when I read what I write it make sense to me but not to the other. My boss always corrects me when I write assembly procedures, test procedures, test reports, compliance testing reports, etc.
 
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Short_Shot

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"The explanation is that the current is in fact limited by state of charge, not the solar." That is what I am trying to explain! as the batteries get full it will draw less current from the source. The source does not force current to the load, the load draws current from the source.
May be I need to improve my English language, it is not my fist language.
Your English is largely fine.

Even for those of us who speak it natively we often can't get the point across properly, or understand what's been presented properly.

The English language sucks even if you're an expert in it and many people clearly are not experts, so it just gets worse.
 

eXodus

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The explanation is that the current is in fact limited by state of charge, not the solar.
This,

I'm charging my 200AH LFP from a 180A alternator without any DC to DC wizardry and it never exceeds 60A in charging - and that's only with almost empty batteries.

When the batteries more then 50-60% full it crawls down to like 30-40A.
his is a 280ah lithium phosphate battery pack
your battery is not big enough to use to full output of the DC to DC. Increase the battery size and you can take advantage of the full output.
 

Posplayr

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Now that the dust has settled somewhat, I'm going to summarize a few things for the OP who seems to be questioning whether or not he is getting 60 amps out of his 60 Amp Dc-DC charger. See the title of this thread: "60a DC-DC Charger only pulling about 40a"

First off 60 amps is a lot of current to be trying to push into anything (loads or batteries), and there is a variety of reasons why the Dc-DC charger does not achieve the rated 60 Amps at the output. I will summarise them:

  1. As Bud Martin has tried to stress, there are factors that will limit how much current a battery will accept. Of course, most people would realize that a fully charged battery will not accept much additional current and especially for any typical configuration (<200 Amp-Hr) will not take 60Amps fully charged. If we consider Bud Martin's insistence on the battery as a limiting factor in the specific case of LiFePO batteries, then the significance tends to the irrelevant. Again there is a presumption that the reader will already understand the point about trying to force current into a fully charged battery. This is due to the fact that there is a generally held principle that for the majority of the LiFePO4 operation region, the battery will absorb most of the current you try to push into it. The details of this "common knowledge" is embedded in the specifics of the charging profiles which have functions of SOC and Charging voltage. So to conclude, if you are trying to assess the performance of a DC-DC converter and assuming your LiFePO4 battery is not fully charged, there are other factors than the battery that would limit current at the DC-DC output.
  2. My own contribution to this discussion is to clear up what seems to be a point of confusion for the OP related to the operation of a DC-DC charger. Without this fundamental knowledge, trying to understand the DC to DC operation is going to be very difficult. Because the DC-DC charger is a Buck-Boost device the specified 60Amp output current is not, in general, going to be the same as the input current. Therefore the only way to determine the output current is to necessarily measure the output current directly. Given the quoted measurements by OP "The last few times i ran the truck and the dc-dc charger i saw anywhere from 40-55 amps", it is certainly not clear if this is input our output or whether OP even realizes there is a difference. To add further confusion the OP concluded that : "at this point , my battery is almost always full , ill take the 40amps and its fine" he is concluding must have had 40 amps of charge current because his battery was fully charged. Here against we have another tell that the OP does not understand the basic operation of a battery charger. The battery could be charged and he never even saw 40A.
  3. Assuming OP was able to measure the DC-DC output charging currents/voltage directly and then compare that to the input charging currents and voltage, he would be able to determine whether or not and why if not the DC-DC was not able to deliver a full 60 Amps at the output. As Exodus has indicated the alternators can easily be the limiting factor in this power conversion process.
  4. It is established fact that the energy demand for alternators can be excessive when charging LiFePO4 batteries through a DC-DC charger! Why ? It is because of the generally very low impedance of LiFePO4 batteries in comparison to Lead-Acid and the high input demand currents for DC-DC Buck-Boost Chargers required when the input voltage is below the output voltage. Why might this cause a DC-DC Charger to not achieve rated output? Because the alternator can not achieve the required DC-DC input requirements to meet the specific output current.
  5. I will continue to harp on the subject of Buck-Boost because the layman apparently does not associate the notion of DC-DC conversion with the current boosting behavior of this conversion process. In my previous example below: We can see that a theoretically ideal conversion with 12V in and 14.5V out would require an 1.45/12=1.20:1 boost in the input current to deliver the specified load current. If you consider a somewhat pessimistic however realistic conversion efficiency of 80% this current boosting goes from 20% to 51%! Realize that the longer the wires from your battery to the DC-DC charger the bigger the voltage drop which requires even more current which continues to drop the voltage even lower requiring more current.
>>>>For example, if you want 14.5V out @40Amps (to the Haus battery) but there is only 12V available at the input to the DC-DC the the input current to DC to DC (i.e. the output current from the car battery/alternator ) will jack up (14.5/12.0)/0.8*40 = 1.46*40 Amps = 58 Amps

As I have mentioned in doing this analysis, using a 3% voltage loss rule, I would not let the input voltage to the DC to DC drop lower than say 12V. This is because there the process is just too inefficient. Add on to of this a claimed 50% alternator efficiency (see teh Vciron Video on this and there is a 100% increase in demand from the alternator!

What even makes this situation worse is that the DC-DC convertors will boost voltages as low as 8V! Redoing the example above this would result in 14.5/8/0.8= 2.26X load current and 4.5X Alternator Power!

In all these cases the DC-DC converter is more than likely putting too much demand on the alternator and so the specified DC-DC output will never be achieved.
 
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eXodus

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Assuming OP was able to measure the DC-DC output charging currents/voltage directly and then compare that to the input charging currents and voltage, he would be able to determine whether or not and why if not the DC-DC was not able to deliver a full 60 Amps at the output. As Exodus has indicated the alternators can easily be the limiting factor in this power conversion process.
I might have described that incomplete. I haven't concluded that it is the alternator.

Just there is something in the chain which limits charging, even without a DC-DC in place - you would think that a direct connection will pull full available capacity from the alternator (180A in my truck) to the battery - but that is not the case. There is a potential that an alternator designed to charge Lead is just not good in charging LFP. Which is OK, prevents them from burning up. (Lead in parallel, NEVER remove the Lead in a Alternator system)

especially for any typical configuration (<200 Amp-Hr) will not take 60Amps fully charged. If we consider Bud Martin's insistence on the battery as a limiting factor in the specific case of LiFePO batteries, then the significance tends to the irrelevant.
when you charge below optimal charging voltage for LFP - it will still charge - but slower then possible.
 

Posplayr

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Just there is something in the chain which limits charging, even without a DC-DC in place - you would think that a direct connection will pull full available capacity from the alternator (180A in my truck) to the battery - but that is not the case.

The whole point of the Dc-to-DC charger is to improve the delivered current to a LiFePO4 battery over what can be achieved by a direct connection. It does this by boosting the output voltage which necessarily requires more input current!

These demands can be high and stressful or reach the limit of the alternator system.
 

Posplayr

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The whole point of the Dc-to-DC charger is to improve the delivered current to a LiFePO4 battery over what can be achieved by a direct connection. It does this by boosting the output voltage which necessarily requires more input current!

These demands can be high and stressful or reach the limit of the alternator system.
This thread is getting kind of depressing. The simplest explanation for what you need is a DC to DC converter is because of the high currents the LiFePO4 can accept. When you couple this with a long run of wire there are substantial voltage drops. So say for instance that you have 14V output from your alternator and for whatever the 3% load drop is you lose just 1V. That means you are at 13V at the lifePO4 battery and it simply will not charge.

Even if you have 14.5 at the alternator, and you start to carry currents approaching 20 amps over a long run (15-20 ft of 10 awg) you can easily lose an additional 0.5V and be at the same 13V at the LiFePO4 terminal and again the battery will not charge.

So the point (i.e. the functionality) of the DC to DC is to boost the voltage (from 13v up to 14v for example) to a defined charging profile for the battery type you have regardless of the input voltage (down to spec limits of for example 8V).

What I am describing is the most benign case and the voltage drops will increase in proportion to the increases in input currents at the DC-DC. As described before this is somewhat of a slippery slope that you need to pull more current because you are pulling more current (more current reinforces the need for more current) and you quickly have high demands for alternator current.
 

eXodus

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The whole point of the Dc-to-DC charger is to improve the delivered current to a LiFePO4 battery over what can be achieved by a direct connection. It does this by boosting the output voltage which necessarily requires more input current!

These demands can be high and stressful or reach the limit of the alternator system.
many people in this board are more concerned about burning out their alternators because too much current is being pulled.
You are one of the first one's to concerned about too little being pulled.

I agree with your point, just that we have different objectives. My main one was - to charge from the alternator without damaging it. I found that it's not really a problem with a small LFP bank.

While your goal is - to charge as fast a possible?
 
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