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Old 11-23-2020, 09:58 AM   #1
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DC to DC Charger and lithium

Let me start by saying I'm not a gear head. I'm a 77 year old beginner who hasn't found a mechanic I can trust to work on my Pace Arrow motorhome.

I know the issue has been discussed many times and almost always the suggestion is to use a DC - DC charger to reduce amps to the batteries and eliminate the possibility of damage to the alternator. Most of the threads I've read are about charging the lithium batteries in a travel trailer rather than a motorhome. Also, many of the posts are from owners of trucks that have newer technology smart alternators. So I think I understand their need.

By comparison, my 2005 Pace with it's 8.1 Chevy has an old technology alternator which I believe puts out considerably more amps than either a similar 2005 Chevy truck or a newer truck with a smart alternator. I've also seen the Victron video of an alternator heating up and smoking because it's unable to adequately dissipate the heat build up while at slow speeds. I also read there is a risk of overheating the wire from the alternator to the batteries when using a more powerful alternator.

So with that in mind rather than a DC to DC charger, which increases charge time of lithium why not use an appropriate alternator with a heavier gauge wire?
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Old 11-23-2020, 10:13 AM   #2
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I'm no expert but, The way I understand it is:

The issue is not so much the charger's ability to produce, but keeping itself from burning up at low rpm. They use an internal fan to keep cool and normally the alternator reduces output while at idle and so the fan is sufficient. But with lithium the draw is not reduced at idle and the fan cannot push enough air to keep it cool.

Hope this helps you understand.
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Old 11-23-2020, 10:16 AM   #3
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You could possibly do that, but you could also go with a Lithium BIM, like THIS.
It would be a lot less expensive than the new alternator, and would guarantee that the alternator wouldn't still burn up.
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Old 11-23-2020, 10:44 AM   #4
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I have observed that our alternator (160a spec) only charged our lithium battery at about 60a-70a under normal driving. The voltage regulator or a built-in module might limit the output to protect the alternator. 5 years with lithium no problem.
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Old 11-23-2020, 10:51 AM   #5
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I have observed that our alternator (160a spec) only charged our lithium battery at about 60a-70a under normal driving. The voltage regulator or a built-in module might limit the output to protect the alternator. 5 years with lithium no problem.

CountryFit,


Are your batteries Battle Born brand? As I hear they have a built in regulator.
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Old 11-23-2020, 10:56 AM   #6
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From what I've seen, the problem with going directly from the alternator to the battery bank is trying to keep the voltage at precisely the ideal charging voltage.

Using a DC-to-DC charger puts a true smart charger in control of things and will mean precise voltage levels to the lithium batteries regardless of engine speed or alternator output. You can get DC-to-DC chargers with high output, so this shouldn't be a limiting factor.
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Old 11-23-2020, 11:08 AM   #7
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CountryFit,


Are your batteries Battle Born brand? As I hear they have a built in regulator.
No, not Battle Born. I bought CALB lithium cells and built the pack. Couple years later Battle Born was born . My pack has a BMS, so does Battle Born.
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Old 11-23-2020, 11:19 AM   #8
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Originally Posted by richard5933 View Post
From what I've seen, the problem with going directly from the alternator to the battery bank is trying to keep the voltage at precisely the ideal charging voltage.

Using a DC-to-DC charger puts a true smart charger in control of things and will mean precise voltage levels to the lithium batteries regardless of engine speed or alternator output. You can get DC-to-DC chargers with high output, so this shouldn't be a limiting factor.
Voltage precision is less concerned actually. Almost all 12v alternators are set at 13.6v output from the factory. Lifepo4 accepts charges without harm up to 14.6v. What importance is to know you have BMS on the lithium battery so to protect the battery in an unlikely event of voltage regulator failure.
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Old 11-23-2020, 11:23 AM   #9
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Impressive Steven

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Old 11-23-2020, 12:00 PM   #10
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I had installed a cut off switch on the alternator leg. But a few times I forgot to turn it off until couple hundred miles later . Then I started to watch the monitor to see how much the current flowing into the battery when DW was driving. There I realized not to worry about it .
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Old 11-23-2020, 01:07 PM   #11
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rather than a DC to DC charger, which increases charge time of lithium why not use an appropriate alternator with a heavier gauge wire?
Have you priced a high output alternator, shoehorning it into the engine bay and rewiring your DC supply (cables, isolation relay, et al) to handle that elevated current?

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Old 11-23-2020, 01:38 PM   #12
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I have observed that our alternator (160a spec) only charged our lithium battery at about 60a-70a under normal driving. The voltage regulator or a built-in module might limit the output to protect the alternator. 5 years with lithium no problem.
This is encouraging. I don't know how to determine the amps that are being put out by the alternator. How do you do it?

We have 2 Lion Energy 1300's 100 Ah batteries that have built in BMS so hopefully that will protect the batteries if we exceed the 14.6 - 8 maximum.

Did you do anything to the wire from your alternator to the house batteries? I know a Country Coach has more house batteries than our Pace so yours may already have a heavier gauge wire.
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Old 11-23-2020, 01:49 PM   #13
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You could possibly do that, but you could also go with a Lithium BIM, like THIS.
It would be a lot less expensive than the new alternator, and would guarantee that the alternator wouldn't still burn up.
Wiring the dc to dc charger looks pretty straight forward. But it requires a wire to an ignition source to turn it on. I can probably do the positive and negative leads but wiring to an ignition source is something I'm not sure I want to do. Does a BIM also require a wire to an ignition source?
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Old 11-23-2020, 01:55 PM   #14
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I have a victron 712 on my battleborn lithium batteries, when connected directly to alternator have seen 130 amps from alternator to batteries from a 160 amp alternator, too much current for me especially at idle speeds, Depending on type of lithium battery and their BMS's, some will accept a high charging rate and some will not. Battleborn's will accept a 1C charging rate which is 100 amps. I installed a dc-dc charger which not only limits the current, but will boost the 13.2 nominal voltage [when start battery is fully charged] to the 14+ volts necessary to bring them to 100% SOC.
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