Lifepo4 on the ctek d250s

[GeekOKent]

Doing a bit of research and it looks.like the ctek d250s is perfect for lifepo4's that have a BMS built in. It will flood at 14.4v/20A and the BMS will basically shut off before the ctek gets to it's float.

Disable the temp control, add a smartpass, and it's all the charging bits needed. Solar+alternator, starter pair and a lifepo4.

So what am I missing, why are people spending a ton of money buying super specialised lifepo4 charge controllers? Is that to compensate for a lack of BMS ?

 

[Jacob100]

Um, pass.

 

[fbnss]

#copiedmymate

 

[Jon Wildsmith]

The voltage profile of a lifepo4 may confuse the CTEK 250S as to what state of charge it's in, so you may get absorption or float stages when you want bulk. The chargers with support for lifepo4 are running a simplified logic in lifepo4 mode, so they should always be in the right mode (bulk or float). If you already have the CTEK, give it a try and let us know how it goes. It might work just fine.

 

[fbnss]

I thought the "s" had a lithium mode on it?

 

[Jon Wildsmith]

That's the newer SE.

 

[Towpack]

The voltage profile of a lifepo4 may confuse the CTEK 250S as to what state of charge it's in, so you may get absorption or float stages when you want bulk. The chargers with support for lifepo4 are running a simplified logic in lifepo4 mode, so they should always be in the right mode (bulk or float). If you already have the CTEK, give it a try and let us know how it goes. It might work just fine.

That's the only reservation I would have. You'd essentially be running two charge controllers, both monitoring and adjusting current and voltage, to charge the same battery so they could end up "fighting" each other. The point of having a LiFePo4 battery with bulit in BMS is so you can connect to a straight DC supply from the alternator or whatever, without the worry of charging problems.

 

[GeekOKent]

@Towpack for a large part of its life the battery is going to be solar charged / topped up.

That's the bit I am hoping I can leverage the d250s for, in addition to when we are moving. A 100w solar should, if my calculations are correct, give me enough juice through the year to run the ambient load via a 50ah lifepo4.

So I am going to try and get to a 100ah, and that should work for the weekends and camping trips where there is extra load too.

@Jon Wildsmith battery on order, along with chunky cables. Will report how it goes.

 

[GeekOKent]

Had a word with the sterling power folks yesterday, who say that putting a lifepo4 battery directly on the alternators 'dirty voltage' invalidates the warranty. He didn't want to comment on the ctek, he didn't know of it, but did say that many DC to DC chargers are also not usable. Only battery to battery chargers are recommended.

I thought DC to DC were battery to battery!

Also had an email back from ctek saying that only the 250SE should be used, not the 250S or the 250SA.

 

[karl2000]

Only battery to battery chargers are recommended.

I thought DC to DC were battery to battery!

Whats a battery to battery charger then?!

 

[Towpack]

I'm assuming "battery to battery" charger means a charger powered by another battery. The charger I bought for the portable 12v LiFePo4 pack I built from 4 Headway cells, can be powered by 240v mains or a 12v supply, either another battery or 12v DC source.
If the manufacturer says not to connect their battery/BMS to an alternator the it can't be aimed at vehicle use. The drop in replacement 12v LiFePo4 vehicle batteries state no such limitation.

 

[GeekOKent]

It's taken a while, but I now have a couple of fogstar drift 105ah 12v Lifepo4 batteries.

Good news, the ctek 250s -does- charge at full whack, when used with the 100w solar. The BMS on the battery itself is then able to workout when to stop, when to charge etc.

Bad news, when on the alternator the batteries do not go into 'charging state'. The ctek is trying to be smart, and the BMS does not like smart.

 

[Jon Wildsmith]

I'd been wondering how you got on with this, so thanks for the update.