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Old 01-31-2019, 08:45 PM   #1
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Lithium Battery and Charger Questions

For various reasons, I'm thinking I'll be going with a Lithium battery bank on our short bus. As for usage, in the short term, I'd like to power a laptop for up to 10 hours a day (65W max), our water pump (Shurflo 408 sufficient for a navy shower and a little water at the sink, a couple LED lights for a few hours, and a phone charger. I'd like to try to run these for up to 2 days between charges, at which point I'd plug into a 110v outlet to charge. For now we'll use all 12v wiring and outlets in the bus (12V adapters for the phone and computer).

I'll be looking at adding solar to augment any shore power charging we would do, and eventually an inverter and 110V wiring, but for simplicity and cost, that'll come later -- just a 110V shore charger is all for now.

Anyway, this raises a number of questions I'm not sure of...

1. Would a 50 amp-hour battery be sufficient for this load? I understand with a lithium battery, I should expect about 40 amp-hours usable power, maybe a bit more, as they can take ~85% DoD.

2. If (when?) I add more power after a year or two, does it hurt to add a second battery to the bank at that time? I know with traditional batteries, it's best to get all new at one time, but with lithium it's cost-prohibitive, so if that's the case here as well, better to get more battery up front. If not, I'd rather save the up-front cost for now.

3. It seems hard to find shore power chargers and solar MTTP chargers designed for lithium batteries. So far I've found a couple made by AIMS (but the shore power charger comes with an inverter I don't need now, along with the extra cost). Are there other stand-alone 110V chargers or MPPT solar chargers that I should consider that are good for lithium batteries?

4. If I'm plugged into shore power, will a 110V charger continue to work to charge the battery while I'm drawing from the battery for the items above?

Thanks in advance!
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Old 01-31-2019, 08:55 PM   #2
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I'm also looking into a lithium based solution as well. I'm still in the planning phase, so take what I say with a grain of salt. In terms of solar charger I believe the Victron line should provide all that is necessary. And for your #4 point, you should be able to charge your batteries and still use them just fine. You'll just be getting to a full charge at a slower rate.

I wish lithium batteries didn't have the hefty cost associated with them since they provide so many benefits! But what's a guy to do
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Old 02-01-2019, 12:43 AM   #3
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No, that laptop usage looks like 100Ah per day, 150Ah if you want 2, would be more like it.

To really **know**, run off an old car battery with a 10+A charger running, measuring per 24hrs with an Ah counter off the batt output.
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Old 02-01-2019, 07:35 AM   #4
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Quote:
Originally Posted by farok View Post
Would a 50 amp-hour battery be sufficient for this load?
Spend a couple bucks and get yourself a Kill-A-Watt meter, connect it to your laptop for a couple days, and find out exactly how much power it consumes over time. Based on my years of powering a laptop from RV/bus battery bank, I bet you will find that it doesn't use an awful lot. When my laptop battery is very low, it will suck a lot of juice (similar to advertised) but when above 80% or so (from memory) it is drawing very little power and even less when laptop battery is 100%.


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Originally Posted by farok View Post
3. It seems hard to find shore power chargers and solar MTTP chargers designed for lithium batteries. So far I've found a couple made by AIMS (but the shore power charger comes with an inverter I don't need now, along with the extra cost). Are there other stand-alone 110V chargers or MPPT solar chargers that I should consider that are good for lithium batteries?
Lithium most certainly presents a different set of challenges for a charger. I re-programmed my Morningstar TS-MPPT-60 to match my lithium bank. I'm not sure if there is a 'best option' available but the better units can be set to work acceptably.

For almost two years, my lithium bank has been charged ONLY via solar. Largely because I rarely have shore power but also because I was nervous about damaging my battery bank. I ran a bit low a couple times last winter so I ordered a Progressive Dynamics PD9125-24LV (24 Volt, 25 Amp charger for lithium) late last fall. However; I haven't installed it yet (haven't needed to) so afraid I have no real data about it.

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4. If I'm plugged into shore power, will a 110V charger continue to work to charge the battery while I'm drawing from the battery for the items above?
The short answer is yes. However; that is a poor and inaccurate answer.

The charger (also known as a charger/converter) provides X voltage and up to a maximum of Y amps (and that varies depending on the charging 'mode' that the charger has decided is appropriate). Where that power goes depends on the charge state of the battery and the amount of power being demanded by the bus. In most cases, some of that power goes to power the bus and some of it goes into the battery. You cannot draw power from a battery and simultaneously charge it.
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Old 02-01-2019, 02:05 PM   #5
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Thanks all for the good info. I'll get a Kill-A-Watt the next time I order something online, and let that be the true judge of power usage. I tend to keep the battery charged, so hopefully it's not a big deal to run it.

Thanks for the info on Morningstar and Victron MPPT charge controllers - they both look good so far! I like that you can program them according to the battery.

For charger/converters, it looks like Progressive Dynamics offers one as you note, but there's not a whole lot of customization on it. The Victron chargers don't seem to be configurable and have a slightly lower charge rate than recommended by most batteries (14.2v instead of 14.4 or 14.6v), so I'm not sure there either. I'll keep looking around, aside from the AIMS that I found as well. Any concern with charging only at 14.2v and then floating at 13.5v?

Any thoughts on whether adding additional battery capacity down the road will degrade the performance of the battery bank to the "least good" of the lot, like traditional cells, or if that's not an issue?

I appreciate all the great info!
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Old 02-01-2019, 02:28 PM   #6
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Another charger option to consider would be the Iota DLS "IQ" smart chargers.

https://www.iotaengineering.com/IQ/#!/
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Old 02-01-2019, 06:08 PM   #7
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Killawatt is for shore power, AC only.

You want to measure the DC Ah used per 24 hours, including overhead of inverters, converters etc

Watts Up is one, but there are lots of generic ones on eBay.

Coulomb counter, AH counter
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