Clark’s hooking up lead and lithium batteries together

A forum for discussing topics relating to MacGregor Powersailor Sailboats

Moderators: kmclemore, beene, NiceAft, Catigale, Hamin' X

Post Reply
User avatar
ris
First Officer
Posts: 488
Joined: Sat Feb 28, 2015 4:27 pm
Sailboat: MacGregor 26X
Location: Frostproof Florida

Clark’s hooking up lead and lithium batteries together

Post by ris » Tue Jan 12, 2021 10:56 am

Just watched Emily and Clarks adventure on YouTube in which Clark talks about hooking up lithium and lead acid batteries into one bank. Never heard of this before but Clark seems to be a smart fellow. It is an interesting concept. Anyone here with an electrical background that can comment on how he did this.
Richard

User avatar
Inquisitor
First Officer
Posts: 494
Joined: Mon Apr 23, 2007 5:24 pm
Sailboat: MacGregor 26M
Location: North Carolina Mountains

Re: Clark’s hooking up lead and lithium batteries together

Post by Inquisitor » Tue Jan 12, 2021 4:56 pm

ris wrote:
Tue Jan 12, 2021 10:56 am
Just watched Emily and Clarks adventure on YouTube in which Clark talks about hooking up lithium and lead acid batteries into one bank. Never heard of this before but Clark seems to be a smart fellow. It is an interesting concept. Anyone here with an electrical background that can comment on how he did this.
Richard
It so happens the YouTube you mention was put up for review on another forum I freuqent this past Saturday. https://diysolarforum.com/threads/hybri ... ead.16759/ There are all types of people on it... from PhD's to electrical engineers, to electrical technicians to DIY off-grid people. As of just now, the comments are mostly positive with some caveats. Some of the really heavy-hitter, theoretical types haven't weighed in and will likely be mulling it over. I don't think it has ever crossed their minds.

I'm on the learning curve on that site and understand most all the aspects he is basing. Some things, I would reflect on his video. He is being conservative in his explanations... basically to keep his audience safe that probably has NO experience with Lithium. Which is TOTALLY expected and good for our audience on this forum as well. But...

Every one of the "problems" he mentions about LiFePO4 batteries is true about the CELLS. However, a top quality BMS will protect the cells from EVERYONE of those problems completely, transparently to the point... you just don't even need to know the problems exist. The only one problem that can throw you for a loop (if you are only familiar with lead-acid batteries) is the cold charging issue. You cannot charge the LiFePO4 batteries if they are below freezing. A good quality BMS will simply not allow you to do it. If you don't know that, you will think your battery is broke. If you simply warm it up, the BMS will start charging it again.

Everything else makes sense about this video about the relative charge voltages, rest voltages, voltage versus capacity curves that makes his system sound plausible. I was going to keep my Lithium and Lead-acid separate as there are some other issues he did not go over in that video and I'd like to see how those are addressed on the other forum. For instance:
  1. As he mentioned, the BMS protects the batteries from over charging. It simply opens the charging circuit. This is no big deal for solar panels. It is however deadly to our boat alternators having no electrical load - Fries the rectifiers. With his system, I would think when the Lithium BMS disconnects, the lead acid will be there to keep on absorbing. Thus, this system sounds like it would be great!
  2. As he also mentions, Lithium will absorb every amp like a fire hydrant. This is fine for solar panels. For our little outboard alternators, it will eat it up and roast it in short order. If the lithium is fully charged (as in 1 above) everything is great and the high internal resistance of the lead-acid will keep from abusing the alternator. However, if the lithium needs charging (and the BMS is on) it will suck every amp my puny 18 amp alternator can deliver until it burns up. There are extra electronic components to take care of this, but that is something I haven't started researching and why I was going to play conservative and just keep the two chemistries separate.
Odysseus, expert on the Siren's call

User avatar
kurz
Captain
Posts: 967
Joined: Mon Dec 06, 2010 9:07 am
Sailboat: MacGregor 26M
Location: Zürich, Switzerland, Europe

Re: Clark’s hooking up lead and lithium batteries together

Post by kurz » Wed Jan 13, 2021 12:17 am

all the new batteries will maybe interesting.

I have no experience with it, but maybe you should charge the lifepo4 with ab battery to battery loader that does not take more than 8 amps... to protect the ob charger.

And it could be just as a second battery so that all time there is a battery connectect to the ob to protect the ob systems...

User avatar
Inquisitor
First Officer
Posts: 494
Joined: Mon Apr 23, 2007 5:24 pm
Sailboat: MacGregor 26M
Location: North Carolina Mountains

Re: Clark’s hooking up lead and lithium batteries together

Post by Inquisitor » Wed Jan 13, 2021 3:35 am

kurz wrote:
Wed Jan 13, 2021 12:17 am
all the new batteries will maybe interesting.

I have no experience with it, but maybe you should charge the lifepo4 with ab battery to battery loader that does not take more than 8 amps... to protect the ob charger.

And it could be just as a second battery so that all time there is a battery connectect to the ob to protect the ob systems...
:D We might be having a translation problem. I Googled "ab battery to battery loader" and got:
Image

I believe a good solution would be different for different situations. For instance...
  1. In my case, I mostly sail. I have 64 hours on my OB in 14 years. Based on my usage pattern, it was far cheaper and easier to keep the two systems isolated. The solar panels charge the lithium house battery and the OB charge the lead-acid starter battery. For long periods (off-season) I'll use one of these to trickle charge the lead-acid from the house battery side.
    https://www.amazon.com/Converter-13-8V- ... B07X9Y5MXT
    Image
  2. If I remember correctly, ris (and Admiral) enjoy their boat strictly motoring. In their case it would seem to be a waste to not utilize the alternator's charging ability. That side, I haven't researched much yet. My cursory understanding now, is lead-acid resistance goes up as it reaches a fully charged state, so the alternator sees a reduced current draw... may only be a 1/4 amp. Light duty alternators assume this light duty cycle and the components are smaller and cheaper. If used at 100% duty cycle for too long it will overheat and burn out. Lithium battery resistance is in the milli-ohm range ALL the time. It draws every amp the alternator can make. From what I understand, there is an electronic device available that with a heat sensor placed on the alternator, will artificially create a less than 100% duty cycle to maximize charging, but allow the alternator to rest, yet keep some load so the alternator doesn't get a voltage spike.
Odysseus, expert on the Siren's call

User avatar
ris
First Officer
Posts: 488
Joined: Sat Feb 28, 2015 4:27 pm
Sailboat: MacGregor 26X
Location: Frostproof Florida

Re: Clark’s hooking up lead and lithium batteries together

Post by ris » Wed Jan 13, 2021 4:08 am

Inquisitor and Kruz thanks. For some time we have been thinking of ways to lower our battery weight from 240 lbs. The 240 lbs is not a hardship but both the boat and the trailer might perform slightly different if you could just lower the weight by say 120 lbs just by changing the battery set up. Two lithium and 1 lead acid would weigh about 120. Our Trojan 105's are still doing great after 5 years of use so this is mostly wishful thinking on my part but I do kind of like the idea.
Richard

User avatar
BOAT
Admiral
Posts: 4818
Joined: Fri Oct 19, 2012 5:12 pm
Sailboat: MacGregor 26M
Location: Oceanside, CA MACMJ213 2013 ETEC60

Re: Clark’s hooking up lead and lithium batteries together

Post by BOAT » Wed Jan 13, 2021 10:28 am

I have lead acid battery under the hood in the Sprinter van and lithium batteries in the house section of the van and they both charge from the alternator when driving. BattleBorn Battery Company sent me the needed equipment to do this. It included a battery to battery charge unit.

The B to B unit connects directly to the lead battery under the hood. The alternator sends it's usual 13.6 to 14 or so volts of power to the lead starter battery under the hood and the B2B unit takes some of that power and turns it into a higher voltage like 14.6 to 15 volts and then sends that higher voltage power to the lithium batteries in the coach.

The lead acid battery never sees the 14.6 voltage and the van alternator is never asked to provide the high voltage - it's all handled by the B2B unit.

I also have a huge perko switch between the lithium batteries and the lead battery that is always in the OFF position.

If for some reason the lead battery dies I can put the perko to the ON position and start the van from the lithium batteries (for emergency only).

You can't really connect the alternator on a 2004 Sprinter to the 2018 Lithium Batteries because they will ask too much from the old fashioned alternator and shorten it's life.

Rumor is that BattleBorn had developed a lithium battery that will work with old alternators and I am contacting them next seek to discuss it.

As od today you need a B2B to do it.

Post Reply