Battery bay dimensions

[nebster]

Hey Newmar Friends,

For our next coach, I'm going to replace the standard bank with lithium batteries. I'm sourcing cells now, and it'd be handy to know the approximate usable dimensions on a Dutch Star or possibly a London Aire battery bay.

I know those bays can hold 8x 6v golf batteries, and those things are about 7 inches in the short dimension, so the bay must be at least 28 inches across. But if any of you are near your bank, or have measured it, could you eyeball and advise as to how much usable height and depth there is?

If it helps, the batteries I'm looking at are harvested from old Teslas and are 26 inches wide, 12 inches deep, and about 3 inches tall. I'm thinking maybe just stack them up like pancakes, either 4 or 6 high depending on how much space is available.

Thanks!

Ben

[Arizona Lizards]

Hi Ben, may not be relative to what you are asking. But we just had solar installed, part of what we changed out were the batteries to lithium ion. The installer placed the new ones on the passenger front storage bay, he said that the lithium would be better in a sealed compartment versus the open battery bay. We then converted the old bay to storage.

[nebster]

Originally Posted by Arizona Lizards

Hi Ben, may not be relative to what you are asking. But we just had solar installed, part of what we changed out were the batteries to lithium ion. The installer placed the new ones on the passenger front storage bay, he said that the lithium would be better in a sealed compartment versus the open battery bay. We then converted the old bay to storage.

Thanks, it's definitely relevant, and I'm glad you brought it up.

I don't have any strong preference to use the battery bay -- it's not sealed, so I have to put an enclosure in. And I don't think it's insulated, so I'll at least have to add a heating pad for the cold. On the other hand, the weight is like-for-like, so it keeps the W&B the same, and the necessary wires are guaranteed to be run the right way already.

But converting it to storage would also offer some advantages beyond coddling the lithium batteries inside, because I think the bay is easier for frequent access vis a vis the under-bed area, for example.

[Luv2go]

Lithium batteries don't like being charged below freezing, so you definitely want to "coddle" them in a conditioned space. I have them in an uninsulated basement compartment and ended up insulating and heating them so I could have peace of mind when using them in winter.

Have you had a look at evtv.me? Jack has done extensive research on Tesla batteries and may give you some good insights. One thing he has recommended is to use the BMS, it makes the battery pack much more safe. This is coming from a person who normally does not recommend BMS at all.

[nebster]

Originally Posted by Luv2go

Lithium batteries don't like being charged below freezing, so you definitely want to "coddle" them in a conditioned space. I have them in an uninsulated basement compartment and ended up insulating and heating them so I could have peace of mind when using them in winter.

Yeah, I'm pretty familiar with all the envelope constraints from all my e-bikes, e-skateboards, etc. I was also had one of the Roadsters back in 2008, so I've been around the block a little.

I've come to the following conclusions, but perhaps you can convince me otherwise:

1. The charging hardware that's available off the shelf and broadly successful in the marketplace today doesn't offer any programmable temperature-probe-charge-shutoff options. What's worse, even if I tried to roll my own frankenstein probes and controller, I'm likely to have to end up managing three completely different charging sources: the inverter/charger, the solar charger, and the alternator. Yuck.

2. On the other hand, I'm not likely to end up with a sub-freezing pack very often. The batteries have huge thermal mass, so as long as I can keep the bay not too cold, we're unlikely to see things get too chilly in our typical camping. A little insulation and a heating pad ought to be able to maintain things in all but the most unusual scenarios for us, since I'm not planning on going boondocking in Winnipeg in January or anything.

I'm curious how you've found your insulation and heating to work out. My quick math suggested it was not going to be a big deal. But, certainly, putting them inside the coach would eliminate the issue entirely.

Have you had a look at evtv.me? Jack has done extensive research on Tesla batteries and may give you some good insights. One thing he has recommended is to use the BMS, it makes the battery pack much more safe. This is coming from a person who normally does not recommend BMS at all.

I haven't, but thanks for the link. My battery pack provider is telling me that they strongly recommend NOT using an active BMS. Even they are a little scientifically fuzzy, though, since there are multiple things the "M" can mean in that acronym.

But I tend to believe them: once the packs are balanced and calibrated, if I stay at 80% discharge in the range from [15%,95%], then unless I have a freak cell take out a pack, I suspect they will stay remarkably close. I'm planning on running them conservatively, because there's plenty of energy -- 32kWh nominal, or about 25kWh usable. We'll put 1.2-1.6kW of solar on the roof and be pretty good, I expect.

I'll definitely take a look through this guy's stuff, though, and see if I can figure out why he reaches the opposite conclusion!

Ben